Comparison of the Diagnostic Utility of Manual Screening and the ThinPrep Imaging System in Liquid-Based Cervical Cytology
Zühal ÖZCAN1, Elife KIMILOÐLU2, Ayþenur AKYILDIZ ÝÐDEM2, Nusret ERDOÐAN3
1Department of Pathology, Haydarpasa Numune Education and Research Hospital, ISTANBUL, TURKEY
2Gaziosmanpasa Taksim Education and Research Hospital, ISTANBUL, TURKEY
3Istinye University, Faculty of Medicine, ISTANBUL, TURKEY
Keywords: ThinPrep Imaging System, Liquid-based cervical cytology, Manual method
To compare the diagnostic results of the ThinPrep manual method (TPMM) and ThinPrep automated method (TPAM) in liquid-based
cytology and present the advantages and disadvantages of both methods.
Material and Method: A total of 1.500 randomized ThinPrep Pap tests that were screened manually and archived in 2015 were reviewed by a
blinded researcher manually and by the ThinPrep automatic method.
Results: There was a 83.3% increase in the detection of ASCUS (Atypical squamous cells of undetermined significance) with the TPAM
compared to the TPMM, and with respect to the reference results, the accuracy was higher for the TPAM than for the TPMM. We also noted
a 33.3% increase in the rate of LSIL (Low grade squamous intraepithelial lesion) and 20% increase in the rate of HSIL (High grade squamous
intraepithelial lesion) by the TPAM. Concordance was best between the TPAM and reference cytologic diagnoses. The sensitivity was higher
for the TPAM and the specificity was similar for both methods. The false positive rate was higher for the TPAM than the TPMM but the false
negative rate was higher for the TPMM. We determined a 30% gain in screening time per smear by the TPAM. However, rejection of many
samples by the system, especially because of air bubbles, was a limitation of the TPAM.
Conclusion: The TPAM has advantages over the TPMM as well as disadvantages such as limiting features and a high false positive rate. The
TPAM should be supported by the manual method to decrease the false positive rate.
Cervical cancer remains the most important public health
problem in developing countries and in Turkey. It was the
fourth most frequent type of cancer seen among women
worldwide in 2012, and more than 500,000 new cases and
266,000 estimated deaths related to the disease have been
reported every year (1). Cervical cancer is a preventable type
of cancer because of the length of its pathogenetic process
and the presence of a preinvasive period. Prevention and
treatment of cervical cancer depend on the detection of its
risk factors and the eradication of preventable ones, the
realization of optimal screening tests appropriate for the
age group, and the establishment of early diagnosis and
The Food and Drug Administration has approved many
liquid-based cytology techniques in recent decades (3).
These methods differ from classical Papanicolaou smears in many aspects. ThinPrep (HOLOGIC) is one such method,
and the ThinPrep Imaging System (TIS) is an automated
imaging and review system that selects “22 fields of view”
from the samples presented to it. The manufacturers
of the TIS particularly note that the system aims to help
cytopathology specialists by highlighting areas of a slide for
further manual review and that the product is not intended
as a replacement for manual review (4). When compared
with conventional cytology, the relative true positive and
false positive rates are 1.13 and 1.12, respectively. This
indicates that the ThinPrep test has a high sensitivity but
low specificity (5). This technique is more expensive than
the classical Pap smear test; however, since it is a more
sensitive test, the requirement of longer between-screening
intervals balances its higher cost. Liquid-based cytology
can decrease the rate of false negative results arising from
errors made during screening tests and from interpretation
of cytological test results (6).
In the present study, we aimed to compare 1500 randomized
ThinPrep slides by using the TPMM and the TPAM. Our
study differs from other similar studies by using the same
ThinPrep Pap smear samples to compare the two methods
and the same samples for reference screening.
The study was conducted in accordance with the principles
of the Helsinki Declaration and approved by the local
Institutional Review Board (08.07.2015).
A total of 1500 ThinPrep slides that were randomly
selected and were then screened and diagnosed manually
by 7 different researchers and archived in 2015 at the
‘Gaziosmanpasa Taksim Education and Research Hospital’
were included in the study. The Pap tests were rescreened
manually (TPMM) then pre-screened on a ThinPrep 2000
device (Cytyc Corporation, Boxborough, MA, USA) and
rescreened again only for “22 fields of view” on a TIS
microscope at x10 magnification (TPAM) by the same
blinded, inexperienced researcher (assistant doctor) to
compare the diagnostic results and the positive/negative
sides of the two methods.
ThinPrep Imaging System
A barcode that includes the protocol number and the year
data was placed on each ThinPrep slide and prescreened
by the same inexperienced researcher from the above
section with the TIS. Eventually, data from 22 fields of
view for each slide were obtained by and stored on the
system. During that process, the system refused to screen
some of the slides for a variety of reasons, such as ‘bubble
artifacts’. Approximately 300 pap smears that were not
recognized or refused to be read by the device were kept in
a xylene solution to remove the probable artifacts following
careful replacement of their cover slips. Subsequently,
approximately 70 pap smears were refused by the device
again and therefore excluded from the study. Another 70
new pap smears were randomly selected from the database
that was archived in 2015 and included in the study (this
preserved the original number of slides as n=1500).
ThinPrep Manual Method
Pap smears were rescreened on a TIS microscope by
the TPMM by the same inexperienced researcher. Each
day, an average of 100 slides were reviewed. Screening
was performed without knowledge of the individual
histopathologic results. While screening, cases were grouped
into reproductive, premenopausal or perimenopausal and menopausal categories. Slides were classified according to
the Bethesda 2014 classification.
ThinPrep Automated Method
Pap smears were rescreened on a TIS microscope at
x10 magnification over “22 fields of view” by the same
inexperienced researcher. Each day, an average of 130
slides were reviewed. Screening was performed without
knowledge of the first pathologic results or the results
obtained by the TPMM. Slides were classified according to
the Bethesda 2014 classification.
A total of 91 cases that were diagnosed as “Epithelial cell
anomaly” on the original cytopathology reports from
2015 or by the TPMM or the TPAM were screened again
by an experienced consultant doctor (reference), and the
new diagnoses were accepted as the gold standard. For the
cases that were diagnosed with “No intraepithelial lesion or
malignancy (NILM)” on the original cytopathology reports
from 2015 or by the TPMM or the TPAM, the original
cytopathology diagnoses from 2015 were accepted as the
Data were reported as percent values as appropriate.
Group comparisons were performed using Fleiss’ kappa
and Krippendorff’s alpha tests. If the same results were
obtained, Cohen’s kappa was calculated to determine the
concordance between two tests. A two-sided p-value <0.05
was considered statistically significant. The reference values
for the concordance between all three tests were as follows:
Unimportant (0.20), Low (=0.20 - 0.40), Median (=0.40 -
0.60), Important (=0.60 - 0.80), and Very important (=0.80
- 1.00). For optimal statistical dual and triple concordance
analyses between the results of the screening methods
and the references, we excluded two cases that were
diagnosed as “Atypical glandular cell (AGC)” only by the
TPMM and three cases that were diagnosed as “Atypical
squamous cells, cannot exclude HSIL (ASC-H)” only by
the TPAM. Additionally, four cases that were diagnosed
as “unsatisfactory for evaluation” by the two methods were
not included in any comparison analysis.
The mean age of patients corresponding to the 1500 cases
reviewed was 40.0±11.47 (range, 18 to 83) years. A total
of 1328 (88.5%) cases were in the reproductive period,
102 (6.8%) were premenopausal or perimenopausal,
and 70 (4.7%) were menopausal. The “unsatisfactory for
evaluation” rate was 0.3% for both methods (n=4).
The breakdown diagnoses was 1455 (97%) NILM, 14
(0.9%) LSIL, 7 (0.5%) HSIL, 18 (1.2%) ASCUS and 2 (0.1%)
ASC-H by the TPMM; 1432 (95.5%) NILM, 19 (1.2%) LSIL,
9 (0.6%) HSIL, 33 (2.2%) ASCUS and 3 (0.2%) ASC-H by
the TPAM; and 1440 (96%) NILM; 31 (2.1%) LSIL, 6 (0.5%)
HSIL and 19 (1.3%) ASCUS by the reference method.
The ASC/SIL ratio was < 2 for both methods (TPMM=0.9
Diagnostic analysis showed that 26 cases diagnosed with
ASCUS, 6 with LSIL and 1 with HSIL by the TPAM were
all diagnosed with NILM by the TPMM (Table IA,B). There
was no distinct difference between the LSIL diagnoses for
the two methods. However, 7 cases were diagnosed with
NILM, 3 with LSIL and 1 with HSIL by the TPAM were
all diagnosed with ASCUS by the TPMM. There was an
83.3% increase in the detection of ASCUS (n=33 vs. 18)
and a 33.3% increase in the detection of LSIL (n=19 vs. 14)
and a 20% increase in the detection of HSIL (n=9 vs. 7) by
the TPAM versus TPMM (Figure 1). With respect to the
reference results, the accuracy was higher for the TPAM
than the TPMM (Table IIA,B, Table IIIA,B).
Click Here to Zoom
|Figure 1: Distribution of the diagnoses of LSIL, HSIL and ASCUS
with respect to the methods and reference.
Click Here to Zoom
|Table IB: Symmetric measures of the cross-tabulation analysis for Table IA.
Click Here to Zoom
|Table IIB: Symmetric measures of the cross-tabulation analysis for Table IIA.
Click Here to Zoom
|Table IIIB: Symmetric measures of the cross-tabulation analysis for Table IIIA.
Concordance was worst between the TPAM and TPMM
diagnoses (p<0.05 and kappa value=0.495) and best
between the TPAM and reference cytologic diagnoses
(p<0.05 and kappa value=0.631) (Table IV-VI).
The reference diagnoses accepted as the gold standard were
used to calculate sensitivity, specificity, and the false positive
and false negative rates. The sensitivity was higher for the
TPAM (for TPMM=62.5% vs. for TPAM=80%), and the
specificity was similar for both methods (for TPMM=99.6%
vs. for TPAM=98.7%). The false positive rate was higher for the TPAM than the TPMM (for TPMM=0.4% vs. for
TPAM=1.3%), but the false negative rate was higher for
the TPMM (for TPMM=37.5% vs. for TPAM=20%) (Table
We determined a 30% decrease in screening time per smear
by the TPAM. However, the rejection of many samples by
the system, especially because of air bubbles, is a limitation
of the TPAM.
In this study, we attempted to compare the manual and
automated ThinPrep methods. Our study showed that the
TPAM has advantages and disadvantages compared to the
TPMM, such as limiting features and a high false positive
rate, and we conclude that the TPAM should be supported
by the manual method to decrease the false positive rate.
It has been shown that the number of atypical smear
diagnoses increase when using TIS (5,6). In studies that compared the TPMM and the TPAM, similar results for
ASCUS, LSIL and HSIL diagnoses were noted (7-9). In
the present study, we noted a 33.3% increase in the rate of
LSIL and a 20% increase in HSIL by the TPAM compared
to the TPMM, but with respect to the reference results,
the false positive rate was higher for the TPAM than the
TPMM. As a result, the TPMM seems to be more valuable
than the TPAM in this respect. Additionally, there was an
83.3% increase in the detection of ASCUS with the TPAM
compared to the TPMM; however, with respect to the
reference results, accuracy was higher for the TPAM than
the TPMM. The concordance was best between the TPAM
and reference cytologic diagnoses. The low concordance
between the TPMM and reference diagnoses may be related
to the evaluations being performed by an inexperienced
and an experienced pathologist, respectively. In the present
study, in two cases diagnosed as ‘ASCUS’ by the TPAM,
candida was detected by TPMM. Therefore, screening only
with “22 fields of view” can be a reason for the increased
false positive rate for TPAM. The ASC/SIL ratio is a quality
control method for gynecologic cytology results and is
typically between 2-3. The CAP (College of American
Pathologists) identifies the median of the ASC/SIL ratio as
1.7. In our study, the ratio was < 2 for both methods. Similar
studies have reported a range of values between 0.74 and
2.25 (7,8,10,11). Satisfactoriness is the only quality control
method of the Bethesda System. The “unsatisfactory for
evaluation” rate was 0.3% for both methods in our study.
In the literature, varying results of this rate have been
noted (between 0.3% and 3%) (7,8,12-16). Studies in the
literature mainly consist of a great number of cases but
used Pap smears screened by different cytotechnologists
at different times and which were rescreened by different
cytotechnologists to compare the different methods
(7,8,17). Our study differentiates from the others by using
the same ThinPrep Pap smear samples to compare the two
methods and to perform reference screening.
Renshaw and Elsheikh investigated the correlation between
the sensitivity for HSIL in the TIS and the epithelial cell
abnormality (ECA)-adjusted workload and showed that
the performance of the TIS at the threshold for HSIL and
above was negatively correlated with the ECA-adjusted
workload (9). Kitchener et al. argued that monotony could
have been a contributing factor in reduced vigilance while
screening by the TPAM (13). Lozano et al. mentioned that
automated screening causes cytotechnology operators to be
more fastidious in their analyses (8). In the present study,
we reviewed 12 smears per hour with the TPMM and 16
smears per hour with the TPAM.
The most significant methods of clinical efficiency in
screening are specificity and sensitivity. In the literature,
some of the studies accepted follow-up biopsies or
TPMM results performed in different years as a reference
and reported differing results regarding sensitivity and
specificity (12,13,18). In the present study, sensitivity was
higher for the TPAM than the TPMM, and specificity was
similar for both methods. Despite of screening with only
by “22 fields of view” with the TPAM, the sensitivity and
specificity values were high for the TPMM. Additionally,
the high false positive rate for the TPMM compared to the
TPAM and the similar results for accuracy and negative
predictive value between the two tests favor the use of the
Colakkadioglu and Erkilic stated that smear slides were
rejected while screening with the automated system because
of the presence of blood, a small number of cells and air
bubbles (19). In the present study, we excluded a total of 70
slides from the study mainly because of the presence of air
bubbles. It must be emphasized that smear rejection by the
device is an important limitation of TIS.
We are aware that there are clear limitations in the case
series presented here. The main limitation of our study
was its retrospective design. The second limitation is that
the results were restricted to the outcomes from a single
institution. Third, some details of the patients’ history
and factors that may influence the outcome may not have
been completely documented. Due to these restrictions,
the associations presented here should be interpreted with
In conclusion, the TPAM has advantages over the TPMM
as well as disadvantages such as limiting features and a high
false positive rate. The TPAM should be supported by the
manual method to decrease the false positive rate.
CONFLICT of INTEREST
The authors declare no conflict of interest.
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