Current CervicalScreening TechnologyConsiderations:Liquid-BasedCytology andAutomated Screening

JENNIFERRUSSELL, DO,* BARBARAA. CROTHERS, DO,*KEITH J. KAPLAN, MD,* and CHRISTOPHERM. ZAHN, MD†

*Department of Pathology, Walter Reed Army Medical Center,Washington, DC; and †Department of Obstetrics and Gynecology,Uniformed Services University of the Health Sciences, Bethesda,Maryland

IntroductionAfter the introduction of the Papanicolaou(Pap) smear, both the incidence of, and mor-tality from, cervical cancer has decreasedsignificantly, particularly for women indeveloped countries with the medical infra-structure available for mass screening pro-grams. However, the Pap test still has limi-tations, including a false-negative rate thathas been reported to be as high as 50%.1,2

Several sources contribute to this potentially

high false-negative rate. Sampling errormay occur during collection of the Pap testwhen the cervical lesion is not adequatelysampled; these errors can account for upto 90% of false-negative cases.1 Anothersource of error occurs when the diagnosticmaterial does not transfer from the samplingdevice to the slide in conventional smears orto the fluid medium in liquid-based cytolo-gy. This is particularly true for smeared(conventional) slides. The reported percent-age of cells transferred to the slide for con-ventional smears varies from 6.5% to62.5%.3 Inability to fully evaluate the slidedue to obscuring material, whether it isblood, mucus, overlapping cells, or inflam-mation, is also a source of error. Finally,but least commonly, false-negative results

Correspondence: Keith J. Kaplan, MD, Medical Director:Cytopathology, Department of Pathology,Walter Reed ArmyMedical Center, 6900 Georgia Avenue NW, Washington,DC 20307-5001. E-mail: keith.kaplan@na.amedd. army.milThe opinions or assertions contained herein are the pri-vate views of the authors and are not to be construedas official or reflecting the views of the Department ofthe Army or the Department of Defense.

CLINICAL OBSTETRICS AND GYNECOLOGY / VOLUME 48 / NUMBER 1 / MARCH 2005

CLINICAL OBSTETRICS AND GYNECOLOGYVolume 48, Number 1, 108–119� 2005, Lippincott Williams & Wilkins

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may be due to misinterpretation. Manualscreening of cytologic smears is a very time-and labor-intensive process. Due to thesubjective nature of the screening process,there is inherent error in this system. Fur-thermore, fatigue and boredom can affectthe cytotechnologists who screen slides afterhours of viewing these slides. In fact, theClinical Laboratory Improvement Amend-ment (CLIA) of 1988 set workload limitsfor both the cytotechnologist and screeningpathologist to address this problem.4 TheAmerican Society of Cytopathology Labo-ratory Accreditation Program also addressesworkload limits, with more conservativerecommendations than CLIA.5

In an effort to improve the efficacy of thePapanicolaou test as a screening test, varioustechnologies have been advanced. Ideally,automated screening technology could sub-stitute for cytotechnologists for the primaryscreening of cytologic smears. Technologiesthat may decrease false-negative rates asso-ciated with slide preparation have also beendeveloped. This section summarizes currentlyavailable technology, primarily to improvescreening for cervicovaginal neoplasia.

IndicationsThe recommendations for cervical cancerscreening vary, not only internationally,but among professional organizations suchas the American College of Obstetriciansand Gynecologists, the American Collegeof Surgeons, and the United States Preven-tive Services Task Force. Based on increas-ing knowledge of the natural history ofhuman papillomavirus (HPV) infectionsand advances in technology, screeningguidelines have recently (2002–2003) beenmodified. A detailed description of screen-ing recommendations, and data supportingthese recommendations, is provided else-where in this monograph.6

Although these screening recommenda-tions provide general guidelines as to whento start screening, how often to screen, andwhen it may be reasonable to stop screening,the actual method of collection (conventional

versus liquid-based) or technology used toassess the test (manual versus automatedscreening) is not addressed. There is one recom-mendation, however, that states that if a pa-tient is considered high-risk, then the Pap testshould be evaluated by manual screening.7

Liquid-Based CytologyA significant problem with conventionallyprepared smears is that key cellular featuresmay be masked due to various obscuringfactors as previously described. These sameobscuring factors that potentially interferewith interpretation on manual screeningmay also interfere with automated screen-ing. Thin-layer slides, prepared from liquid-based collection systems, reduce these ob-scuring features. In addition, liquid-basedcytology preparations improve cell transferfrom the collection instrument to the eventu-al slide and produce uniformity of the cellsample.8,9 Two types of thin-layer cytologicpreparations are currently available in theUnited States and are Food and DrugAdministration (FDA) approved: ThinPrep�Pap Test (Cytyc Corporation, Boxborough,MA) and SurePathTM (TriPath Imaging,Inc., Burlington, NC).

THINPREP�In contrast to a conventional Papanicolaoutest, where a brush or spatula is manuallysmeared across a glass slide, the samplingdevice is rinsed into a ThinPrep� vial thatcontains PreservCyt� transport medium.Separate spatulas and brushes or broom-likedevices may be used for sampling. If a sepa-rate spatula is used, plastic, and not wood,spatulas must be used. Collection devicesare vigorously agitated in the collection me-dium prior to discarding the device. Insuffi-cient agitation can result in scantly cellular orunsatisfactory specimens. The vial contain-ing the transport medium is then placed intothe ThinPrep� 2000 or 3000 processor,where a dispersion cycle mixes the specimenand breaks up blood, mucus, and debris.Subsequently, a series of negative pressurepulses generated by a pneumatic system

Liquid-Based Cytology and Automated Screening 109

draw the fluid through a ThinPrep� filter,which results in a thin, even layer of cellularmaterial being deposited on the filter. TheThinPrep� processor ensures that an appro-priate amount of material is collected by con-stantly monitoring the rate of flow throughthe ThinPrep� filter. The material from thefilter is transferred to a glass slide that isthen placed into a fixative bath for staining.The result of this process is a slide that con-tains a circle of diagnostic material 20 mm indiameter that can be analyzed by manual orautomated screening. Compared to a conven-tional smear, ThinPrep� slides are easier toscreen and result in reduced screening times.In addition to providing cellular material forslides, the remaining fluid in the vials can beused for HPV DNA testing or to performtesting for Neisseria gonorrhea or Chla-mydia trachomatis. Testing for gonorrheaand Chlamydia on residual fluid has been ap-proved by the FDA (February 2003) for theThinPrep 2000 processor (not the ThinPrep3000 processor) if appropriate additionaltesting equipment is present.

SUREPATHTM

Formerly known as CytoRich (and synony-mous with AutoCyte), the SurePath Pap Testis another liquid-based preparation methodfor cervical specimens. The sample is col-lected with broom-type device that is imme-diately placed into a vial of preservativefluid. Instead of rinsing the device in the flu-id, the head of the device is popped off intothe vial. The vial is then capped and sent tothe laboratory for processing. The fluid inthe vial is vortexed and syringed to createa mixed liquid cell suspension. This suspen-sion is layered onto a density reagent ina centrifuge tube; centrifugation of the sus-pension through this density reagentremoves debris and inflammatory cells fromthe suspension. The density reagent is dec-anted, and the centrifuge tubes are placed in-to the AutoCyte PREP SystemTM (TriPathImaging) for further processing, which con-sists of mixing and transfer of the centri-fuged cell pellets to small plastic columns

mounted on microscope slides. The cellsare allowed to settle for at least 10 minutes,after which the slides are individuallystained by the processor and then cover-slipped. This process produces a monolayerof cells in a 13-mm area that can be screened.The remaining fluid can also be tested forHPV DNA through the process of laboratoryvalidation against a standard test.

LIQUID-BASED CYTOLOGY:ADEQUACY AND ACCURACY

There is a large volume of data regardingliquid-based cytology and comparison to con-ventional smears in detecting cervical ab-normalities. Regarding specimen adequacy,compared to a conventional smear, the cellsin thin-layer preparations are more easilyviewed because there is less obscuring mate-rial.9 As a result, diagnoses may be more eas-ily made even with potentially fewer availablediagnostic cells.3 Additionally, as described,monolayer slides are more easily screenedand are less frequently inconclusive.

Numerous studies have demonstrated im-proved specimen adequacy with thin-layerliquid-based preparations compared to con-ventional smears.9–18 Adequacy has alsobeen evaluated in a meta-analysis of Thin-Prep compared to conventional smears andis summarized in Table 1. Interestingly,not all studies have shown overall improvedadequacy of thin-layer preparations. In oneseries, overall adequacy for conventionalsmears was 91% compared to 87% for Thin-Prep slides.19 The reasons for inadequacy,however, differed among the preparationmethods. More conventional smears wereinadequate due to obscuring inflammation,thickness of cells, and air-drying, whereasThinPrep slides were limited by the lack ofan endocervical component.19 It is thoughtthat at least in some studies, the lack ofendocervical component may be due to thestudy method (split-sample), as other studiesusing direct-to-vial methods have not dem-onstrated this discrepancy.9,19

Although numerous studies have beenperformed to assess the ability of monolayer

110 Russell et al

technology to detect cervical disease, it isdifficult to create a summary of the resultsdue to different study designs (direct-to-vialor split-sample), different measures of ‘‘effi-cacy’’ (sensitivity/specificity, increase in ab-normal diagnoses, or agreement betweenmethods), and different standards of accuracy(use of cytology or histology as the refer-ence standard). In general, many of thesestudies have shown that liquid-based cytol-ogy is superior to conventionally preparedsmears for the detection of squamous intra-epithelial lesions (SIL).10–12,17–26 Severalstudies are detailed to provide examples ofthe techniques, results, and interpretations.

Monsonego et al evaluated 5248 women,comparing ThinPrep to conventional smearsusing a split-sample technique.19 Theseinvestigators found that ThinPrep diagnosed29% more atypical squamous cells of unde-termined significance (ASCUS), 50% morelow-grade SIL (LSIL), and 18% more high-grade SIL (HSIL) cases. When combiningLSIL, HSIL, and cancer, ThinPrep identified39% more of these diagnoses, which wasstatistically significant (P, 0.001).19 In an-other split-sample study, ThinPrep was com-pared with conventional smears in 478women with biopsy-confirmed abnormali-

ties.27 The 2 methods were concurrent in91.4% of cases. For SIL or cancer, the meth-ods did not differ (P = 0.7). Although sen-sitivity of the 2 methods in diagnosingSIL or cancer was similar (83% for Thin-Prep, 90% for conventional), specificitieswere different (83% for ThinPrep, 70% forconventional smears).27

Bergeron et al compared AutoCyte� Prep(TriPath Imaging) prepared slides to conven-tional smears, using samples from 500 con-secutive women in whom cone biopsy wasperformed for either HSIL or discrepant cy-tology-colpohistology.17 For pooled data,sensitivities and specificities of the 2 methodsin detecting HSIL were similar. However,when evaluating the first samples that weretaken (because consecutive samples wereobtained on each patient), thin-layer slideshad improved sensitivity compared to con-ventional smears (89% versus 79%, respec-tively; P = 0.02); however, specificity waslower compared to conventional smears(36% versus 41%; P , 0.01).17

Renshaw et al compared ThinPrep to con-ventional smears in the College of AmericanPathologists Interlaboratory ComparisonProgram in Cervicovaginal Cytology, whichis a national laboratory-based quality

TABLE 1. Meta-Analysis of Comparison of ThinPrep� and Conventional Cytology

Diagnosis MethodNo.Studies

ThinPrep(All Processors)Rate*

ThinPrep2000 ProcessorRate*

ConventionalSmearRate OR 95% CI†

ASCUS Direct-to-vial 8 3.94% 3.28% 1.03 0.99–1.06ASCUS Split-sample 14 8.25% 7.02% 1.20 1.13–1.27ASCUS Split-sample 4 5.85% 5.59% 1.05 0.95–1.16LSIL Direct-to-vial 8 2.53% 1.05% 2.15 2.05–2.26LSIL Split-sample 17 6.85% 5.52% 1.27 1.21–1.32LSIL Split-sample 6 6.38% 5.09% 1.27 1.21–1.34HSIL Direct-to-vial 8 0.71% 0.30% 2.26 2.06–2.47HSIL Split-sample 17 1.80% 1.66% 1.09 1.00–1.18HSIL Split-sample 6 1.10% 0.94% 1.14 1.00–1.29Adequacy Direct-to-vial 6 87.13% 76.13% 2.11 2.07–2.15Adequacy Split-sample 4 79.55% 70.39% 1.64 1.53–1.76Adequacy Split-sample 3 79.55% 70.22% 1.65 1.54–1.78

Adapted with permission from Bernstein et al.9

*Meta-analysis separately analyzed liquid-based results when performed on all processors and those performed on the ThinPrep 2000processor.

† 95% CI based on pooled odds ratios.

Liquid-Based Cytology and Automated Screening 111

improvement program.25 This programinvolves submission of cytology slides byparticipating institutions that are reviewedand confirmed by at least 3 cytopathologists.The slides may then be used as ‘‘validated’’or ‘‘educational’’ slides. In this report, therewere 89,815 interpretations from conventionalsmears and 20,886 from ThinPrep slides. Inthe ‘‘validated’’ slide group, compared toconventional smears, ThinPrep was associatedwith an overall lower false-positive rate(3.2% versus 1.6%, P = 0.001) and a lowerfalse-negative rate (2.1% versus 1.3%, P =0.02). Interestingly, if only HSIL or cancerwas considered, the false-negative rate wasno different. It has been suggested that itmay be difficult to detect HSIL and cancerin some monolayer preparations due to thedifferent appearance or lack of a tumor di-athesis and that HSIL features may be moresubtle in ThinPrep slides.25,28

Bernstein et al performed a meta-analysisto evaluate adequacy and diagnostic accuracyof liquid-based preparations compared toconventional cytology.9 A total of 25 studiesmet criteria for inclusion; ThinPrep was theliquid-based method evaluated. Both split-sample and direct-to-vial methods wereused. There were 221,864 ThinPrep speci-mens and 378,659 conventionally preparedslides included in this analysis. Two meth-ods of processing ThinPrep specimens wereincluded: a ThinPrep processor beta model(initial processor) and the subsequentlyFDA-approved ThinPrep 2000 processor.The results of this meta-analysis are pre-sented in Table 1. In summary, liquid-basedcytology was associated with improved sam-ple adequacy and improved diagnostic accu-racy for both LSIL and HSIL; however, theASCUS rate was the same.9

Automated ScreeningAnother effort to reduce the potential forfalse-negative Pap tests was the develop-ment of automated screening, both to reducediagnostic errors as well as reduce the tre-mendous workload on laboratories. Not onlyis manual screening labor intensive, it is also

difficult, because out of the thousands ofcells present on a slide, there may be rela-tively few that contain an abnormality.8

Thus, automated screening has been theo-rized as a method to reduce potential risk.

Automated screening has been the sourceof numerous publications for over a decade.Initial efforts using automated screeningwere focused on rescreening of manuallyscreened Pap tests identified as ‘‘normal.’’As a result of the initial data, the FDA, in1995, approved 2 automated screening sys-tems for rescreening those smears found tobe negative by manual screening. These twosystems were the PAPNET Testing System(Neuromedical Systems, Inc., Suffern,NY) and the Neopath Auto Pap 300 QCSystem (NeoPath, Inc., Redmont, WA). Thisrescreening of negative smears also fulfilledthe CLIA criteria for random manual rescre-ening of 10% of negative slides.

TECHNIQUE

PAPNET was a neural network system thatscanned slides and stored digital images ofthose cells or cell regions that had the high-est likelihood of containing an abnormality.These images were then viewed at anotherlaboratory by a trained cytologist and tri-aged as either ‘‘negative’’ or ‘‘review’’ if fur-ther evaluation was deemed necessary. Ifslides were placed in the ‘‘review’’ category,they were screened manually. A pathologistreviewed the abnormal slide to determinethe final diagnosis.

For the AutoPap system (currently alsoknown as the FocalPointTM System; see Ter-minology section), prepared cervical smearsare affixed with a barcode and loaded intotrays that are placed into the slide processor,which first reads the barcode, checks eachslide for physical integrity, then scans andanalyzes the slide. The system contains acomputerized high-speed video-microscope.System integrity is assessed before and aftereach tray of slides for quality assurance.During scanning, each slide is analyzed forspecimen adequacy and morphologic changesindicative of epithelial abnormalities. The

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slide is assigned a score that the device usesto rank the slides based on the likelihoodthat the individual slide is benign, unsatis-factory, or abnormal. The slides are thenclassified into one of the following catego-ries: ‘‘No Further Review,’’ ‘‘Review,’’ or‘‘QC Review.’’ The ‘‘No Further Review’’category consists of slides that are deemedby the system as most likely to be normaland may be archived as ‘‘negative for intra-epithelial lesion or malignancy’’ (NILM)according to the 2001 Bethesda System(TBS); these slides would have been pre-viously categorized as within normal limits(WNL) using older terminology. Slides inthis category require no further review.The system can classify up to, but no morethan, 25% of all successfully processedslides into this category. The remainingslides are then classified as ‘‘Review’’ andrequire manual screening by a cytotechnolo-gist, who screens the slide and classifies it aseither NILM or requiring review by a pathol-ogist. The system also classifies at least 15%of all successfully processed slides as eligi-ble for rescreening. These slides are thosemost likely to contain an abnormality andmay be used instead of the 10% random se-lection of slides for quality control.

For slides in the ‘‘Review’’ category, eachslide is ranked by assigning a score from‘‘1’’ to ‘‘n,’’ where ‘‘1’’ designates a slidemost likely to contain an abnormality and‘‘n’’ (the number of slides in the set) desig-nates the slide least likely to contain an ab-normality in this particular review set. In ad-dition, each slide is placed into a group from1 to 5, with the lower number indicating thegroup of slides with the highest probabilityof containing abnormalities. Slide adequacyis determined by evaluating the cellularity ofthe squamous component the presence of anendocervical component and the degree towhich slides are obscured.

QUALITY CONTROL/RESCREENING

Both of these systems were shown to offerimprovement as quality-control rescreeningmethods to be used after manual screening.

The PAPNET System, as a quality-controlmeasure, detected higher numbers of abnor-mal smears than manual screening withouta decrease in specificity.29 In another studycomparing PAPNET with manual rescreen-ing, PAPNET-assisted rescreening was moreeffective than manual rescreening, reducing(nonsignificantly) the false-negative rate andsignificantly reducing the false-positiverate.30 In a meta-analysis of the performanceof PAPNET, the authors concluded that asa quality-control measure, between 20%and 90% of the manually screened false-negative smears were correctly identifiedas abnormal with PAPNET rescreening.31

Not all studies identified significant im-provement with PAPNET rescreening. In astudy primarily evaluating the cost-effectivenessof PAPNET rescreening compared to manualrescreening, the authors found that very fewadditional abnormal slides were identifiedwith PAPNET.32 Manual review of thoseslides identified by PAPNET as potentiallyabnormal identified 5 cases diagnosed asASCUS and 1 case diagnosed as atypicalglandular cells of undetermined significance(AGUS). Compared to studies reportingmuch higher detection rates, these authorsdistinguished their findings based on studydesign. The investigators noted that in manyof the other studies of automated screening,the slides used were either known abnormalslides or consisted of a group of slides witha high percentage of abnormal specimens. Incontrast, the authors of this report evaluatedover 5000 slides initially diagnosed as‘‘WNL’’ or ‘‘benign cellular changes’’ on pri-mary manual screening and 10% randomrescreening. Thus, the authors concluded thatthe utility of rescreening was highly depen-dent on the prevalence of disease in thescreened population.32

Quality control rescreening with AutoPaphas also been evaluated and has been dem-onstrated to be effective in some studies. Inan early study of rescreening, AutoPap was5 times more likely than manual rescreeningto detect a false-negative smear.33 In a studycomparing AutoPap rescreening to manual

Liquid-Based Cytology and Automated Screening 113

rescreening in over 14,000 cases, AutoPapidentified 3 to 5 times more false-negativesthat random manual screening.34 The sensi-tivity for identifying false-negative casesrose considerably if the threshold for detec-tion was set at LSIL as opposed to anydegree of abnormality.34,35 Stevens et alcompared AutoPap to manual rescreeningat various rescreening rates (such as 10%,20%, etc.) and found that AutoPap was su-perior to manual rescreening, although thestudy was limited due to sample size.36

In a meta-analysis of the AutoPap Systemas a rescreening modality, 5 studies met crite-ria for inclusion. In this analysis, if the qualitycontrol rescreening rate was set at 10% (sim-ilar to manual rescreening), the average sensi-tivity (of identifying a false-negative smear)was 37%.37 These authors noted that therewas, however, a relative paucity of completedata on the use of this system, at least to beconsidered for inclusion in a meta-analysis.37

TERMINOLOGY

Although automated technology was initiallymarketed for rescreening, studies evaluat-ing this technology for primary screeningwere also underway. These studies generallyinvolved the use of the same technology(PAPNET, AutoPap) as rescreening studies.However, in reviewing the data, keepingtrack of the technology and the names ofthe systems can be confusing. AutoCyte,Inc. and Neo Path, Inc. merged to form Tri-Path Imaging, Inc. This merged companyacquired the intellectual property from Neu-romedical Systems, Inc. As a result, thenames of the techniques and equipment havechanged over the years.

Understanding the process involved ina Pap test diagnosis helps to clarify the con-fusion regarding automation terminology.There are 3 components to fully automatedcytotechnology: specimen collection, speci-men processing, and specimen interpreta-tion. Collection of a cytology specimen ina liquid-based medium with subsequent pro-cessing to form a thin layer of cells is anautomated specimen preparation system.

Technically, these are 2 different processes(collection and processing), but they are of-ten referred to as 1. Cytyc Corporation usesThinPrep vials to collect the liquid-basedspecimen and the ThinPrep processor to pre-pare the thin-layer slide. TriPath Imaging,Inc., currently uses the SurePath (previouslyknown as AutoCyte) liquid-based collectionvials and processes the specimen into slideswith PrepStainTM (formerly the AutoCyte�PREP System). The third component of au-tomated technology consists of automatedscreening systems as summarized in the pre-ceding paragraphs. As described, duringearly trials of screening, and in more recenttrials of primary screening, the 2 commonlyused systems were PAPNET and AutoPap.Due to the company mergers describedabove, as well as technological advancesand improvements, the current screening sys-tem for TriPath Imaging, Inc. is the Focal-PointTM System, a modification of the Auto-Pap System. The AutoPap System was alsoknown under different names during the timeperiods of these studies. The instrument eval-uated during the rescreening and some pri-mary screening trials and approved forrescreening was the AutoPap 300 QC sys-tem. A system also described for primaryscreening is the AutoPap Primary ScreeningSystem.

In summary, for ease of interpretation,AutoCyte is synonymous with the currentSurePath System. ThinPrep has maintainedits terminology for both the liquid-based col-lection and thin-layer preparation systems,and the AutoPap automated slide screenersare synonymous with the with the currentFocalPoint system. There are other systemsdescribed; however, much of the publisheddata involves the use of 1 of the systems de-scribed above, and it is helpful to understandthe development of the technology to inter-pret the data and be familiar with the currentlyavailable systems.

PRIMARY SCREENING

Prior to the business developments as previ-ously described, both the PAPNET and

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AutoPap systems were evaluated for use asprimary screening modalities. Several stud-ies noted that screening with PAPNET wasmore likely than manual screening to identi-fy potentially abnormal cells, although theincreased detection included more ASCUSand LSIL; detection of high-grade lesionswas not different.38–40 In a meta-analysisof PAPNETas a primary screening modality,the odds ratio (OR) of detecting an abnor-mality using PAPNET, compared to manualscreening, was 1.19 (95% confidence inter-val [CI]: 1.13–1.26; P , 0.001).31 Thissame meta-analysis also noted a reductionin false-negative interpretations using PAP-NET compared to manual screening (OR0.41, 95% CI: 0.25–0.67; P , 0.005).31

The AutoPap Primary Screening System(Auto Pap 300 QC system) has been ap-proved by the FDA for use as a primaryscreening modality. Two large studies eval-uated the AutoPap System, comparing itto typical manual screening protocols.41,42

In theses studies, automated screening wasfound to be more sensitive in identifyingASCUS and LSIL and equivalent to manualscreening for the detection of HSIL. UsingASCUS as a threshold, the sensitivity of au-tomated screening was 86% compared to79% for manual screening. Using LSILas a threshold, the sensitivity of automatedscreening was 94%; for manual screening,the sensitivity was 84%.43 Both of thesedifferences were statistically significant.For HSIL, the sensitivity of automated andmanual screening (97% and 93%, re-spectively) was not significantly different.Specificity was also improved; automatedscreening was associated with a 16% im-provement in specificity compared withmanual screening.41 More importantly, ofthe slides designated as ‘‘No Further Re-view’’ by automated screening, none con-tained a high-grade lesion.42

In subsequent studies of primary screen-ing with AutoPap applied in clinical prac-tice, the data substantiated the results ofthe large clinical trials.44,45 A study per-formed in a high-risk population also

validated previous data.46 A meta-analysisof AutoPap for primary screening andrescreening was only able to identify 4 stud-ies (of the 14 initially evaluated) that met cri-teria for analysis of its use as a primaryscreening technique.37 In this analysis, thesensitivity of AutoPap as a primary screenerranged from 85% to 100%. Others, however,have not found a significant differencebetween manual and automated primaryscreening, identifying similar sensitivitiesand specificities.47

LIQUID-BASED CYTOLOGY VERSUSCONVENTIONAL SMEARS ANDAUTOMATED SCREENING

Although names applied to the technologyhave changed over time, and the slide andscreening systems are often considered asa ‘‘unit,’’ it is important to understand thedistinction between the type of slide prepa-ration and the screening system. The auto-mated systems were initially designed toscreen conventionally prepared smears. Infact, the initial FDA approval for the Auto-Pap system stated that the system was to beused on conventionally prepared slides.48 Ithas long been recognized by cytology auto-mation vendors that liquid-based prepara-tions would be far easier for automatedscreening instruments to evaluate, but inthe past, reimbursement for liquid-basedPap tests was insufficient, and laboratoriesprimarily processed conventional smears.Recognizing this dilemma, TriPath Imaging,Inc. opted to focus first on automatedscreening of conventional smears while sec-ondarily developing a liquid-based system,whereas Cytyc Corporation proceeded todevelop a liquid-based collection methodprior to an automated screening instrument.Although earlier trials of automated screen-ing involved conventional smears, automatedscreening technology was modified toscreen liquid-based thin-layer slides, andsome of the later screening studies incorpo-rated thin-layer preparations. As thin-layerpreparations were shown to be superior toconventional smears, it appears obvious that

Liquid-Based Cytology and Automated Screening 115

thin-layer and automated technology shouldcomplement each other.49 Automatedscreening of thin-layer slides has been foundto be highly capable of detecting cervicalabnormalities.50 In another study, it wasconcluded that automated screening of thin-layer preparations was superior to screeningof conventionally prepared smears.51

Cost ConsiderationsAlthough automated screening has beenfound by some investigations to have supe-rior sensitivity compared to manual screen-ing (whether used as a primary screeningmethod or for quality-control rescreening),most of the increased detection is at the lowerend of the abnormal spectrum—ASCUSand LSIL. As described, detection of HSILis similar for the various methods. One con-cern, therefore, relates to the clinical signif-icance of increased detection of low-gradelesions as opposed to high-grade lesions.Some have suggested that comparisons ofaccuracy should be primarily based on de-tection of high-grade abnormalities.47

Obviously, increased detection of low-grade abnormalities may increase costs relatedto the need for further clinical evaluation inthese patients. Additional costs includepurchase or lease of the automated screen-ing instrument as well as the slide prepara-tion equipment. Use of any of these tech-nologies adds to the incremental cost ofeach slide screened.52 Offsetting thesecosts are the savings of personnel time re-quired for manual screening, especially forslides designated as ‘‘No Further Review,’’and the potential for increased laboratoryefficiency. Thus, any cost analysis must ac-count for not only the equipment and tech-nology, but also the effect on laboratoryefficiency and avoidance of unnecessaryfollow-up.

When considering costs, the slide collec-tion and processing technology, as well asautomated screening, must be considered.Several analyses have evaluated costs asso-ciated with liquid-based thin-layer prepara-

tions. In one study, it was calculated thatthere was an overall savings in lifetime costsassociated with the use of ThinPrep com-pared with conventional smears.53 The de-crease in cost was attributed to a decreasein the number of follow-up visits, therebyoffsetting technology costs. In another anal-ysis, the decrease in overall cost was relatedto improvements in sampling and adequacy.9

More commonly, cost-effectiveness con-siderations have been applied to automatedscreening, some also in combination withthin-layer preparations. In one study, thecost of AutoPap screening for the detectionof high-grade disease was greater than formanual screening of conventional smears,and the cost differential was dependent onthe number of smears evaluated per yearand on the rate assigned to the ‘‘No FurtherReview’’ category (20%, 25%, or 30%).47 Ina study comparing PAPNET rescreening tomanual screening, the cost of detecting eachadditional ASCUS or atypical glandularcells of undetermined significance (AGUS,under previous TBS terminology) smearranged from $5825 to $33,781, and for eachadditional LSIL smear, costs ranged from$17,475 to $101,393.32 These authors con-cluded that PAPNET-assisted rescreeningidentified a few more ASCUS cases, butat a relatively high cost.32 Another analysisdetermined that biennial PAPNET-assistedrescreening resulted in a cost of $48,474per year of life saved.54 These authors sug-gested that the cost-effectiveness of PAP-NET-assisted rescreening was similar tocost-effectiveness in terms of cost per yearof life saved for other screening tests, suchas mammography performed in womenbetween the ages of 40 and 50 years, orthe use of prostate-specific antigen testingin screening men for prostate cancer.54 Astudy evaluating laboratory costs (cytotech-nologist time, clerical costs), in a comparisonof PAPNET and manual screening, conclud-ed that although PAPNET resulted in timesavings, the effect was outweighed by thecosts associated with scanning the slidesand the additional equipment.55

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Other studies using economic modelshave evaluated these screening technologiesusing varied screening intervals. Hutchinsonet al found that due to increased sensitivitiesof the tests, these technologies resulted incost-effectiveness ratios below $50,000 peryear of life saved at screening intervals of2 years or more.56 Brown and Garber eval-uated over 200 publications, extracting dataregarding sensitivity, specificity, and tech-nology employed, and applied an elegantcost-effectiveness model to those studiesthat met criteria for inclusion.57 It is im-portant to note that this was a study of re-screening, not primary screening. ThinPrep,AutoPap, and PAPNETwere evaluated withthis model. The authors concluded that all 3technologies increased the cost per womanscreened by $30 to $257 (1996 costs) andthat the increased life expectancy rangedfrom 5 hours to 1.6 days.57 Cost-effectivenesswas significantly impacted by screeninginterval and also varied based on the sensi-tivity of the technologies used. A generalconclusion was that these technologies,when incorporated into triennial screening,resulted in more life-years saved at lowercost compared to biennial conventionalPap testing. Of note, annual screening withthese technologies resulted in a cost per yearof life saved of $160,000, compared to$16,259 with triennial screening. Interest-ingly, the cost per year of life saved just de-scribed ($16,259) was associated with theuse of AutoPap; triennial screening withPAPNET resulted in a cost per year of lifesaved of $146,783.

A comprehensive review of cost-effectiveness is beyond the scope of thisreview. Obviously, cost-effectiveness isdependent on prevalence of disease, tech-nologies used, manpower and laboratorycosts, sensitivity and specificity of testingschemes, and other factors. As these tech-nologies expand and new technologies aredeveloped and incorporated into screening,cost analysis will be critical for cost-effectiveimplementation of these technologies intoclinical practice.

SummaryLiquid-based cytology, thin-layer slide prep-arations, and automated screening are onlysome of the advances in cervical cancerscreening. As technology advances, newdevices and technologies will be studiedand promulgated, either as stand-alonemethods or in combination with currentlyavailable technologies, as we have seen withHPV DNA testing and cytology. As thesetechnologies become available, costs willneed to be considered, especially for areasaround the world where access to these tech-nologies may be limited.

References1. Gay JD, Donaldson LD, Goellner JR. False-

negative results in cytologic studies. ActaCytol. 1985;29:1043–1046.

2. Joseph MG, Cragg F, Wright VC, et al.Cyto-histologic correlates in a colposcopicclinic: a 1-year prospective study. DiagnCytopathol. 1991;7:477–481.

3. HutchinsonML, Isenstein LM, Goodman A,et al. Homogenous sampling accounts forthe increased diagnostic accuracy using theThinPrep processor. Am J Clin Pathol.1994;101:215–219.

4. Clinical Laboratory Improvement Amend-ments of 1988: final rule. Federal Register.1992;57:7169–7170.

5. Gupta PK, Erozan YS, Schwartz MR. Amer-ican Society of Cytopathology laboratory ac-creditation program. Arch Pathol Lab Med.1997;121:260–263.

6. Waxman A. Guidelines for cervical cancerscreening: history and scientific rationale.Clin Obstet Gynecol. 2005;48:77–97.

7. Renshaw AA, Lezon KM, Wilbur DC. Thehuman false-negative rate of rescreeningPap tests. Measured in a two-armed prospec-tive clinical trial. Cancer. 2001;93:106–110.

8. Nuovo HM, Melnikov J, Howell LP. Newtests for cervical cancer screening. Am FamPhysician. 2001;64:780–786.

9. Bernstein SJ, Sanchez-Ramos L, Ndubisi B.Liquid-based cervical cytologic smear studyand conventional Papanicolaou smears: a meta-analysis of prospective studies comparing cyto-logic diagnosis and sample adequacy. Am JObstet Gynecol. 2001;185:308–317.

Liquid-Based Cytology and Automated Screening 117

10. Bolick DR, Hellman DJ. Laboratory imple-mentation and efficacy assessment of theThinPrep cervical cancer screening system.Acta Cytol. 1998;42:209–213.

11. Lee KR, Ashfaq R, Birdsong GG, et al.Comparison of conventional Papanicolaousmears and a fluid-based, thin-layer systemfor cervical cancer screening. Obstet Gyne-col. 1997;90:278–284.

12. Papillo JL, Zarka MA, St John TK. Evalua-tion of the ThinPrep Pap Test in clinical prac-tice: a seven-month, 16,314-case experiencein northern Vermont. Acta Cytol. 1998;42:203–208.

13. Carpenter AB, Davey DD. ThinPrep� PapTestTM: performance and biopsy follow-upin a university hospital. Cancer. 1999;87:105–112.

14. Diaz-Rosario LA,Kabawat SE. Performanceof a fluid-based thin layer Pap smear methodin the clinical setting of an independent lab-oratory and an outpatient screening popula-tion in New England. Arch Pathol Lab Med.1999;123:817–821.

15. Wilbur DC, Cibas ES, Merritt S, et al. Thin-PrepTM processor: clinical trials demonstratean increased detection rate of abnormal cer-vical cytologic specimens. Am J Clin Pathol.1994;101:209–214.

16. Corkhill M, Knapp D, Martin J, et al. Spec-imen adequacy of ThinPrep sample prepara-tions in a direct-to-vial study. Acta Cytol.1997;41:39–44.

17. Bergeron C, Bishop J, Lemarie A, et al. Ac-curacy of thin-layer cytology in patients un-dergoing cervical cone biopsy. Acta Cytol.2001;45:519–524.

18. Linder J, Zahniser D. ThinPrep Papanico-laou testing to reduce false-negative cervicalcytology. Arch Pathol Lab Med. 1998;122:139–144.

19. Monsonego J, Autillo-Touati A, Bergeron C,et al. Liquid-based cytology for primary cer-vical cancer screening: a multi-centre study.Br J Cancer. 2001;84:360–366.

20. Hutchinson ML, Zahniser DJ, Sherman ME,et al. Utility of liquid-based cytology for cer-vical carcinoma screening: results of a popu-lation-based study conducted in a region ofCosta Rica wit a high incidence of cervicalcarcinoma. Cancer. 1999;87:48–55.

21. Bishop JW, Bigner SH, Colgan TJ, et al.Multicenter masked evaluation of AutoCyte

PREP thin layers with matched conventionalsmears: including initial biopsy results. ActaCytol. 1998;42:189–197.

22. Vassilakos P, Griffin S, Megevand E, et al.CytoRich liquid-based cervical cytologicscreening results in a routine cytopathologyservice. Acta Cytol. 1998;42:198–202.

23. Vassilakos P, Schwartz D, de Marval F, et al.Biopsy-based comparison of liquid-based,thin-layer preparations to conventional Papsmears. J Reprod Med. 2000;45:11–16.

24. Limaye A, Connor AJ, Huang X, et al.Comparative analysis of conventional Papani-colaou tests and a fluid-based thin-layer meth-od. Arch Pathol LabMed. 2003;127:200–204.

25. Renshaw AA, Young NA, Birdsong GG,et al. Comparison of performance of con-ventional and ThinPrep gynecologic pre-parations in the College of AmericanPathologists gynecologic cytology program.Arch Pathol Lab Med. 2004;128:17–22.

26. Corkhill M, Knapp D, Hutchinson M. Im-proved accuracy for cervical cytology withthe ThinPrep method and the endocervicalbrush-spatula collector procedure. J LowerGenit Tract Dis. 1998;2:12–16.

27. Park IA, Lee SN, Chae SW, et al. Comparingthe accuracy of ThinPrep Pap tests and con-ventional Papanicolaou smears on the basisof the histologic diagnosis. A clinical studyof women with cervical abnormalities. ActaCytol. 2001;45:525–531.

28. Wilbur DC, Dubeshter BM, Angel C, et al.Use of thin-layer preparations for gyneco-logic smears with emphasis on the cytomor-phology of high-grade intraepithelial lesionsand carcinomas. Diagn Cytopathol. 1996;14:210–211.

29. Farnsworth A, Chambers F, Goldschmidt C.PAPNET. An Australian experience of over60,000 cases.Med J Aust. 1996;165:429–431.

30. Bergeron C, Masseroli M, Ghezi A, et al.Quality control of cervical cytology in high-risk women. PAPNET system comparedwith manual rescreening. Acta Cytol. 2000;44:151–157.

31. Abulafia O, Sherer DM. Automated cervicalcytology: meta-analyses of the performanceof the PAPNET system. Obstet GynecolSurv. 1999;54:253–264.

32. O’Leary TJ, Tellado M, Buckner SB, et al.PAPNET-assisted rescreening of cervicalsmears. JAMA. 1998;279:235–237.

118 Russell et al

33. Colgan TJ, Patten SF Jr, Lee JS. A clinicaltrial of the AutoPap 300 QC system forquality control of cervicovaginal cytologyin the clinical laboratory. Acta Cytol. 1995;39:1191–1198.

34. Patten SF Jr, Lee JS, Wilbur DC, et al. TheAutoPap 300 QC System multicenter clini-cal trials for use in quality control rescreen-ing of cervical smears: I. A prospectiveintended use study. Cancer. 1997;81:337–342.

35. Patten SF Jr, Lee JS, Wilbur DC, et al. TheAutoPap 300 QC System multicenter clini-cal trials for use in quality control rescreen-ing of cervical smears: II. Prospective andarchival sensitivity studies. Cancer. 1997;81:343–347.

36. Stevens MW, Milne AJ, James KA, et al. Ef-fectiveness of automated cervical cytologyrescreening using the AutoPap 300 QC Sys-tem. Diagn Cytopathol. 1997;16:505–512.

37. Abulafia A, Sherer DM. Automated cervicalcytology: meta-analyses of the performanceof the AutoPap 300 QC system. Obstet Gy-necol Surv. 1999;54:469–476.

38. Duggan MA. Papnet-assisted, primaryscreening of cervico-vaginal smears. Eur JGynaecol Oncol. 2000;21:35–42.

39. KokMR, BoonME. Consequences of neuralnetwork technology for cervical screening.Cancer. 1996;78:112–117.

40. Ouwerkerk-Noordam E, Boon ME, Beck S.Computer-assisted primary screening of cer-vical smears using the PAPNET method:comparison with conventional screeningand evaluation of the role of the cytologist.Cytopathology. 1994;5:211–218.

41. Wilbur DC, Prey MU, Miller WM. The Au-toPap system for primary screening in cervi-cal cytology. Comparing the results ofa prospective, intended-use study with rou-tine manual practice. Acta Cytol. 1998;42:214–220.

42. Wilbur DC, PreyMU,MillerWM.Detectionof high grade squamous intraepithelial le-sions and tumors using the AutoPap system:results of a primary screening clinical trial.Cancer. 1999;87:354–358.

43. WilburDC,NortonMK.The primary screen-ing clinical trials of the TriPath AutoPap�system. Epidemiology. 2002;13:S30–S33.

44. Bibbo M, Hawthorne C. Performance of theAutoPap primary screening system at Jeffer-

son University Hospital. Acta Cytol. 1999;43:27–29.

45. Bibbo M, Hawthorne C, Zimmerman B.Does use of the AutoPap assisted primaryscreener improve cytologic diagnosis? ActaCytol. 1999;43:23–26.

46. Tench WD. Validation of AutoPap primaryscreening system sensitivity and high-riskperformance. Acta Cytol. 2002;46:296–302.

47. Confortini M, Bonardi L, Bulgaresi P, et al.A feasibility study of the use of the AutoPapscreening system as a primary screening andlocation-guided rescreening device. Cancer.2003;99:129–134.

48. Food and Drug Administration. Second Sup-plement to the Premarket Approval for theAutoPap Device. Pub. No. P950009. Rock-ville, MD: Food and Drug Administration;1998.

49. Stoler MH. Advances in cervical screeningtechnology. Mod Pathol. 2000;13:275–284.

50. Vassilakos P, Carrel S, Petignat P, et al. Useof automated primary screening on liquid-based, thin-layer preparations. Acta Cytol.2002;46:291–295.

51. Bishop JW, Cheuvront DA, Sims KL. Eval-uation of the AutoCyte SCREEN system ina clinical cytopathology laboratory. Acta Cy-tol. 2000;44:128–136.

52. Hutchinson ML. Assessing the costs andbenefits of alternative rescreening strategies.Acta Cytol. 1996;40:4–8.

53. Sedlacek T, Cooper A. Cervical cancerscreening: what is cost-effectiveness? J LowerGenit Tract Dis. 1999;3:S1–S7.

54. Schechter CB. Cost-effectiveness of rescre-ening conventionally prepared cervicalsmears by PAPNET. Acta Cytol. 1996;46:1272–1282.

55. Meerding WJ, Doornewaard H, van Balle-gooijen M, et al. Cost analysis of PAPNE-T-assisted vs. conventional Pap smearevaluation in primary screening of cervicalsmears. Acta Cytol. 2001;45:28–35.

56. Hutchinson ML, Berger BM, Farber FL.Clinical and cost implications of new tech-nologies for cervical cancer screening: theimpact of test sensitivity. Am J Manag Care.2000;6:766–780.

57. Brown AD, Garber AM. Cost-effectivenessof 3 methods to enhance the sensitivityof Papanicolaou testing. JAMA. 1999;281:347–353.

Liquid-Based Cytology and Automated Screening 119