Kulasingam SL, Hughes JP, Kiviat NB, Mao C, Weiss NS, Kuypers JM, Koutsky LA. Evaluation of Human Papillomavirus Testing in Primary Screening for Cervical AbnormalitiesComparison of Sensitivity, Specificity, and Frequency of Referral. JAMA. 2002;288(14):1749–1757. doi:10.1001/jama.288.14.1749
Author Affiliations: Departments of Epidemiology (Drs Kulasingam, Weiss, and Koutsky), Biostatistics (Dr Hughes), Pathology (Drs Kiviat and Kuypers), and Obstetrics and Gynecology (Dr Mao), University of Washington, Seattle. Dr Kulasingam is now with the Department of Obstetrics and Gynecology, Duke University, Durham, NC.
Context Human papillomavirus (HPV) DNA testing of women having Papanicolaou
(Pap) smears showing atypical squamous cells of undetermined significance
(ASCUS) has clinical usefulness. Whether HPV DNA testing alone is useful in
primary screening remains to be determined.
Objective To determine the accuracy of HPV DNA testing for detecting cervical
intraepithelial neoplasia (CIN) grade 3 or cancer (the criterion standard).
Design, Setting, and Participants Between December 1997 and October 2000, 4075 women who attended Planned
Parenthood clinics in Washington State were screened simultaneously using
thin-layer Pap and HPV DNA testing by a polymerase chain reaction (PCR)–based
method and by a liquid-based RNA-DNA hybridization capture with signal amplification
assay (signal amplification). Women who were positive for high-risk HPV types,
or had Pap results of ASCUS or higher, were considered to have positive screening
test results and were referred for colposcopy and biopsy. Additionally, a
random sample of women with negative screening test results was referred for
colposcopy. Based on individual and combined thin-layer Pap, HPV PCR, and
HPV signal amplification test results from the screening and the colposcopy
visits, 7 colposcopy triage strategies were defined and evaluated.
Main Outcome Measure Sensitivity and specificity for detecting cervical lesions graded CIN
3 or higher for each of the 7 triage strategies.
Results The estimated prevalence of CIN 3 or higher was 3.2%. The sensitivity
(95% confidence interval) of thin-layer Pap (with a result of ≥ASCUS) for
identifying women with CIN 3 or higher was only 61.3% (48.5%-70.9%) compared
with 88.2% (78.9%-93.8%) for HPV testing by PCR and 90.8% (83.1%-95.8%) by
signal amplification. Differences in specificities were also observed: 82.4%
(81.8%-83.1%) for thin-layer Pap (with a result of ≥ASCUS), 78.8% (77.9%-79.7%)
for PCR, and 72.6% (69.4%-75.0%) for signal amplification. Compared with referral
for colposcopy of all women with ASCUS or higher, signal amplification testing
of women with ASCUS and referral of those with a positive result was about
as sensitive (61.3% vs 60.3%, respectively) and significantly more specific
(82.4% vs 88.9%, respectively). The strategy requiring repeat positive PCR
tests on 2 visits had a sensitivity of 84.2% (75.3%-91.0%) and a specificity
of 86.2% (85.1%-87.3%). All tests were more specific and less sensitive in
older (≥30 years) vs younger women.
Conclusions Testing for HPV has higher sensitivity but lower specificity than thin-layer
Pap screening. In some settings, particularly where screening intervals are
long or haphazard, screening for HPV DNA may be a reasonable alternative to
cytology-based screening of reproductive-age women.
Concern about the low sensitivity of the conventional Papanicolaou (Pap)
smear has prompted a search for newer methods to either supplement or replace
it.1- 3 A recent
review concluded that 47% of women who developed invasive cervical cancer
have had adequate screening histories within 5 years of detection.4 Some women failed to follow up on an abnormal smear
result, while many had a history of negative smear results. The Bethesda system
for reading and interpreting cervical cytology specimens was introduced to
improve the accuracy of Pap smear diagnoses.3 However,
the diagnostic categories introduced by the Bethesda System appear to be no
more reproducible than diagnostic categories of other systems.5- 7 Another
concern is the high proportion of smears (over 10% in some populations) read
as atypical cells of undetermined significance (ASCUS) and the fact that 5%
to 10% of women with this diagnosis have an underlying high-grade lesion.8
Human papillomavirus (HPV) is now established as a cause of cervical
cancer.9,10 In particular, persistent
detection of high-risk HPV types is a strong predictor of development of high-grade
cervical precancer and invasive cervical cancer.11- 13
A handful of studies, to date, have examined the role of testing for
HPV DNA in primary screening. Most of these studies did not refer women with
completely negative test results to colposcopy, so the resulting measures
of sensitivity may be overly optimistic. In addition, no measures of specificity
can be calculated.14,15 One study
of 2098 Canadian women, reported by Ratnam et al,16 did
include referral of women with completely negative test results to colposcopy.
The estimated sensitivity of HPV DNA testing was higher than that of conventional
Pap smear (68.1% vs 40.2%). The estimated specificity of Pap testing was 91.6%
compared with 90.6% for HPV DNA testing.
The thin-layer Pap technique was introduced in the early 1990s. It may
have a higher sensitivity than the conventional Pap smear and allows for HPV
testing of residual liquid that remains after a cytology slide has been made.17 Despite this improved sensitivity, triage studies
of women with Pap smears graded as ASCUS indicate that, compared with a repeat
thin-layer Pap smear, a test for high-risk HPV types has a better sensitivity
for detecting high-grade lesions or cancer.8,18 A
comparison of the accuracy of thin-layer Pap vs HPV DNA testing in primary
screening has not yet been reported.
Testing for HPV DNA may be more specific in older vs younger populations.
While HPV DNA is commonly detected in cervical specimens of sexually active
women younger than 30 years and may indicate transient infection, it is detected
less often in women older than 30 years, where it is more likely to be associated
with high-grade lesions or cancer.14
The present study was undertaken to evaluate the potential of HPV testing
for improving screening accuracy for detection of high-grade lesions or cancer
among a population of women of reproductive age and to see whether the level
of accuracy varies by age. Two different assays for HPV DNA testing were compared:
a polymerase chain reaction (PCR)–based assay and a liquid-based DNA-RNA
hybridization capture with signal amplification assay (signal amplification).
From December 1997 to October 2000, 4358 consecutive women presenting
for annual examinations at 1 of 3 Planned Parenthood clinics in Washington
State were invited to participate in the study. Women who were 18 to 50 years
of age were eligible if they had no history of hysterectomy, chronic immune
suppression, or treatment for cervical neoplasia. Women who provided written
informed consent were enrolled. The University of Washington Institutional
Review Board approved all protocols.
After consent was obtained, a standardized questionnaire was used to
collect demographic, reproductive, and sexual history information. A gynecologic
examination was then performed, and screening test samples were obtained according
to the following protocol. For cervical cytology, an Ayres spatula was used
to collect cells from the transformation zone and a cytobrush was used to
collect endocervical cells. Both the brush and the spatula were repeatedly
tapped and rinsed in PreservCyt (Cytyc Corp, Boxborough, Mass) for processing
the final thin-layer cytology slide (ThinPrep, Cytyc Corp). Next, a specimen
for HPV DNA testing was obtained by rotating a dacron-tipped swab in the endocervical
os and swabbing it on the ectocervical epithelium. This swab was placed in
standard transport medium (STM) (Digene, Gaithersburg, Md). All STM specimens
from the screening visit were tested for HPV DNA by PCR. Prior to January
2000, STM specimens from the screening visit of the 712 women who attended
colposcopy were tested for HPV DNA by signal amplification (Hybrid Capture
2, Digene). Starting in January of 2000, HPV DNA signal amplification testing
of residual thin-layer Pap liquid from all screening visits was introduced
(n = 1150). No change was made to the specimen collection protocol.
Before April 1999, a urine sample was collected (n = 1533). Poor sensitivity
and a high proportion of inadequate samples (data not presented) led to a
decision to stop collecting urine for HPV testing.
Women were referred for colposcopy and biopsy if they had ASCUS, atypical
glandular cells of undetermined significance (AGUS), low-grade squamous intraepithelial
lesion (LSIL), or high-grade squamous intraepithelial lesion (HSIL) or higher
on thin-layer Pap; or a positive PCR test result for high-risk HPV types.
A 45% random sample of the first 1000 women with negative Pap and HPV DNA
test results was invited to have colposcopy performed. This high percentage
was initially selected to determine rates of colposcopy participation. Oversampling
for this group continued, however, due to low participation. Of 2631 women
with negative cytology and HPV results, 1079 (41%) were randomly selected,
and 202 (7.7%) had colposcopy performed. In January 2000, with the initiation
of screening by signal amplification, women who were positive for high-risk
HPV types by signal amplification were also referred for colposcopy. All women
eligible for colposcopy were telephoned a minimum of 3 times and sent a letter
when telephone contact failed. The average time between the screening visit
and the colposcopy visit was 3 months.
At the colposcopy visit, a detailed standardized questionnaire was completed
and cervical samples for thin-layer Pap and HPV DNA testing were obtained
as outlined above for the screening visit. One of 2 experienced colposcopists
performed colposcopy using the DenVu computerized colposcopy system (DenVu,
Tucson, Ariz). Ectocervical biopsies of visible lesions (or the 12 o'clock
location if no lesion was visible) were obtained. Endocervical curettage was
performed when the lesion extended into the endocervical canal, the Pap test
showed HSIL but the lesion was not visible on colposcopy, or the Pap test
showed AGUS. Women with histologically confirmed cervical intraepithelial
neoplasia (CIN) grade 2 or 3 or invasive cervical cancer were referred for
treatment. Women with HSIL on thin-layer Pap and less than CIN 1 on histology
underwent repeat biopsy. Women with CIN 1 returned to Planned Parenthood for
Thin-layer slide preparation and processing was performed according
to the manufacturer's specifications (Cytyc Corp). The thin-layer slide was
then stained with the Papanicolaou stain, screened by a cytotechnologist (certified
by Cytyc), and reviewed by pathologists at Harborview Medical Center in Seattle,
Wash, having no knowledge of other laboratory or clinical data. Smears were
classified as unsatisfactory based on finding more than 60% of the slide target
area without epithelial cells. Cellular changes were classified according
to the Bethesda classification system as negative, ASCUS, AGUS, LSIL, HSIL,
or suggestive of cancer.19 A random 10% sample
of all slides read as normal was rescreened manually as mandated by federal
Hemotoxylin-eosin–stained slides of the biopsy tissue were prepared
and reviewed by the pathologist without knowledge of other clinical or laboratory
data. Diagnoses were assigned using both the CIN and Bethesda classification
HPV DNA PCR amplification reactions were performed using 5′ biotinylated
MY09, MY11, and HMB01 primers (Invitogen Co, Carlsbad, Calif) and Amplitaq
Gold polymerase (Applied Biosystems, Foster City, Calif). To prevent PCR product
carryover, dTTP was replaced by dUTP and uracil-N-glycosylase
was added. The human β-globin gene was coamplified in the HPV reaction
mix using 5′ biotinylated primers PC04 and GH20 to monitor specimen
adequacy. Two microliters of each specimen was added to 100 µL of reaction
mix. Amplification by PCR was carried out in a TC 9600 thermal cycler (Perkin
Elmer, Wellesley, Mass) with the following profile: 95°C for 9 minutes
to activate the polymerase; 40 cycles at 95°C for 1 minute, 55°C for
1 minute, and 72°C for 1 minute, and a 5-minute terminal extension at
HPV DNA typing analysis was performed according to the manufacturer's
specifications21 using the reverse-line strip
test (Roche, Emeryville, Calif) to detect high-risk HPV types 16, 18, 26,
31, 33, 35, 39, 45, 51, 52, 55, 56, 58, 59, 68, 73, 82, or 84.
The signal amplification test was configured to detect in a single assay
one or more of the following high-risk HPV types: HPV 16, 18, 31, 33, 35,
39, 45, 51, 52, 56, 58, 59, or 68. Prior to January 2000, the assay was performed
according to the manufacturer's specifications on residual screening STM samples
(after the aliquot for PCR was removed) from 712 women who returned for colposcopy.
Starting in January 2000, testing of residual PreservCyt liquid was performed
on all screening samples (n = 1150). A positive result was recorded for specimens
with a relative light unit of 1 or greater, corresponding to 5000 or more
HPV DNA copies.
As configured and performed in this study, both the PCR and the signal
amplification assays had analytic sensitivities of 10 to 100 copies of HPV
DNA per sample.
Estimates of sensitivity and specificity for detection of CIN 3 or higher
and of the percentage of women referred for colposcopy were obtained for 7
screening strategies. These strategies included referral for colposcopy of
women with the following positive test results: (1) a screening thin-layer
Pap test showing LSIL or higher or a screening thin-layer
Pap test showing ASCUS with a follow-up thin-layer Pap test showing ASCUS
or higher; (2) a screening thin-layer Pap test showing ASCUS or higher; (3)
a screening thin-layer Pap test showing LSIL or higher or a screening thin-layer Pap test showing ASCUS with a screening PCR
test result that was positive for high-risk HPV types; (4) a screening thin-layer
Pap test showing LSIL or higher or a screening thin-layer
Pap test showing ASCUS with a screening signal amplification test result that
was positive for high-risk HPV types; (5) a screening PCR test result that
was positive for high-risk HPV types; (6) a screening and follow-up PCR test
result that was positive for high-risk HPV types; or (7) a screening signal
amplification test result that was positive for high-risk HPV types.
A strategy of repeat testing for high-risk HPV DNA by signal amplification
could not be evaluated because only 163 women had these results for both the
screening and follow-up visits.
To calculate sensitivity and specificity, 2 × 2 tables were generated
using results from the screening and colposcopy visits. Analyses were first
performed using the total population and then separately for women younger
than 30 years and for women aged 30 years or older. The definition of a positive
screening test result was based on the strategy-specific criteria for referral
for colposcopy. Depending on the strategy, women with an abnormal Pap result
(≥ASCUS) or high-risk HPV DNA were categorized as test positive. Women
with negative results (including women who were positive for low-risk HPV
types) were categorized as test negative. Since women with inadequate Pap
results are usually asked to return for a repeat test, Pap and HPV DNA test
results that were inadequate, missing, or insufficient were initially coded
as positive. A sensitivity analysis was performed to determine how coding
the inadequate, insufficient, and missing results as negative affected the
estimates of sensitivity and specificity. Additional sensitivity analyses
were based on the use of CIN 2 or higher as the criterion standard, and on
separate analyses for signal amplification prior to and after January 2000
to account for differences in specimen collection and testing.
Using the screening results, we defined "screening strata" based on
the 6 possible combinations of thin-layer Pap results (ASCUS/LSIL, HSIL, normal)
and PCR result (positive/negative for high-risk HPV DNA). For women with normal
Pap and negative PCR results, we deliberately invited only a random subsample
to return for colposcopy. Analyses indicated that the likelihood of referral
for colposcopy depended on the perceived severity of the screening results.
Thus, estimates of sensitivity, specificity, and prevalence that ignore these
sampling issues will be biased. It is possible to correct for this bias when
estimating sensitivities, specificities, and prevalence. Further details in
each case are provided below.
To determine the expected number of women testing positive by signal
amplification overall and prior to 2000, the number of positive screening
signal amplification samples was divided by the sampling fraction for each
screening stratum. Summation across all strata provided an estimate of the
total number of positive results that would have been obtained if all women
screened had been tested by signal amplification.
Uncorrected sensitivity, corrected sensitivity, and corrected specificity
were calculated as follows. Uncorrected sensitivity was calculated with the
usual formula for sensitivity:
where ni is the number of true positives
who returned for colposcopy in the ith stratum and xi is the number of those true positives that
screen positive. The sums are over 5 of the 6 screening strata. Specifically,
we omit the stratum of women who screened negative by both Pap and PCR. Thus,
uncorrected sensitivity refers to calculations based only on women who returned
for colposcopy and who had a positive screening result for at least 1 of the
tests. Such estimates can only be used to determine whether more cases were
associated with a positive result on one test than on another test. The lack
of outcome information for women with negative results for both tests means
that there is incomplete information for the total number of false-negative
results and true-negative results for each test (ie, there is verification
Corrected sensitivity was calculated from the following formula:
where fi is the proportion of those
in screening stratum i who return for colposcopy.
Corrected specificity was defined analogously.
The corrected sensitivity and specificity estimate the sensitivity and
specificity that would have been obtained if all women who were screened had
returned for colposcopy. Within each screening stratum, the distribution of
lesion grades among those who did and did not return for colposcopy was assumed
to be the same. This is a plausible assumption, since HPV DNA and thin-layer
Pap results were the only factors found to be independently associated with
both return for colposcopy and detection of CIN 3 or higher. Other potentially
confounding factors, including age, race/ethnicity, education, income, number
of sex partners, hormonal contraceptive use, time between screening and colposcopy
visit, and parity, were not independently associated with both colposcopy
attendance and detection of CIN 3 or higher (data not shown).
Means, medians, and SDs were calculated for continuous variables. Differences
in proportions were tested using the χ2 test. Univariate and
multivariate logistic regression analyses were performed to estimate odds
ratios (ORs) and 95% confidence intervals (CIs) for colposcopy attendance
and high-grade histology results. Variances and 95% CIs for corrected sensitivities
and specificities were calculated using bootstrap resampling in which the
sampling fractions were considered fixed.22 All
analyses were performed using STATA 7.0 (STATA Corp, College Station, Tex).
Of 4358 eligible women, 4075 (93.5%) were enrolled. These women were
a mean age of 25 years (SD, 5.7), were predominantly white, and reported a
lifetime median of 6 sex partners (range, 0-148) (Table 1). Compared with women younger than 30 years (n = 3310),
women aged 30 years or older (n = 760) reported a higher lifetime number of
sex partners (median of 5 vs 9, respectively), and higher incomes (median
of $800 vs $1100 per month, respectively). Older and younger women were similar
in terms of race/ethnicity, parity, use of oral contraceptives, and education.
The screening thin-layer Pap results of 678 (16.6%) of 4075 women were
abnormal (Table 2). High-risk
HPV DNA was detected by PCR in screening samples of 747 (18.3%) women, of
whom 231 (31%) women were infected with multiple types (including high- and
low-risk types). Among women who were positive for 1 or more high-risk types,
HPV type 16 was the most common type detected (28.7%, n = 214), followed by
HPV type 52 (13.2%, n = 99) and HPV type 51 (11.4%, n = 85). HPV type 18 was
detected in 8.4% (n = 63), HPV type 45 in 4.9% (n = 37), and HPV type 31 in
7.1% (n = 53) of women screening positive for HPV DNA.
Extrapolation of the screening signal amplification results of 712 women
who returned for colposcopy to all women screened prior to 2000 provided a
high-risk HPV DNA prevalence estimate of 26%. The prevalence estimate for
the 1150 women who were screened post-2000, when signal amplification screening
results were available for all women, was 28.5%. Since these 2 prevalence
estimates were similar, the weighted estimate (27.4%) that was based on a
weighted summation of the percentage positive within each screening cytology
and PCR stratum was used in calculations of sensitivity and specificity for
all strategies that included a signal amplification test.
The percentages of women with different cytologic findings who were
positive by PCR for high-risk HPV types were as follows: 82.0% (91/111) with
HSIL, 64.4% (104/166) with LSIL, 35.7% (143/401) with ASCUS, 12.0% (398/3318)
with normal cytology results, and 11.3% (9/79) with inadequate cytology specimens.The
estimated percentages (in the overall population) of women who had positive
results by signal amplification were as follows: 85.6% (95/111) for HSIL,
81.9% (136/166) for LSIL, 47.4% (190/401) for ASCUS, and 20.5% (680/3318)
for women with normal smear results.
The prevalence of HPV (by PCR) increased in women aged 18 to 24 years
and then declined sharply (Figure 1).
The prevalence of LSIL declined steadily with increasing age. The prevalence
of ASCUS averaged approximately 10% across all age categories. The estimated
prevalence of histologically confirmed CIN 3 or higher increased slightly
with increasing age.
Of the 1015 women who had biopsies performed, 87 had results of CIN
3 or higher (Figure 2), including
1 woman with endocervical adenocarcinoma in situ. Sixty-four (73.6%) of these
lesions were detected in women younger than 30 years. The results for women
with lower than CIN 3 were as follows: 50 had CIN 2, 185 had CIN 1, 137 had
atypia, and 556 had negative histologic findings.
Three women (ages 30, 32, and 34 years) with CIN 3 or higher diagnosed
by biopsy were found to have microinvasive cancer in the specimen from the
loop electrosurgical excision procedure and subsequently underwent hysterectomy.
All 3 were positive for HPV DNA by signal amplification and had HSIL Pap results
at the time of screening. Two of the 3 women were PCR-positive at screening;
all 3 were PCR-positive at their colposcopy visit.
The corrected (for colposcopy attendance and verification bias) estimate
of CIN 3 or higher prevalence in this population was 3.2%. The 3 screening
strategies that were based on testing for high-risk HPV DNA by PCR or by signal
amplification were significantly more sensitive than any of the 4 strategies
that included thin-layer Pap (84.2%-90.8% vs 57.2%-61.3%) (Table 3). However, the specificity estimates for the HPV DNA detection
strategies tended to be lower than for those of the thin-layer Pap–based
strategies (72.6%-86.2% vs 82.4%-89.9%). Compared with referral for colposcopy
of all women with ASCUS or higher, signal amplification testing of women with
ASCUS and referral of those with a positive result was about as sensitive
(61.3% vs 60.3%, respectively) and significantly more specific (82.4% vs 88.9%,
respectively). A single signal amplification test for high-risk HPV DNA referred
the highest proportion of women for colposcopy. Compared with strategies that
required repeat Pap or HPV DNA testing of women with ASCUS, the referral strategy
based on repeated PCR positivity for high-risk types was significantly more
sensitive (84.2% vs 57.2%-60.3%) but significantly less specific (86.2% vs
Although the differences were not significant, all screening strategies
were more sensitive for CIN 3 or higher among women younger than 30 years
than for women aged 30 years or older (Table 4). Estimates of specificity, however, were significantly
higher for women aged 30 years or older than for those who were younger than
30 years. Similar results were obtained when CIN 2 or higher was used as the
definition of high-grade disease, and again all sensitivity estimates for
those aged 30 years or older were lower than for those younger than 30 years.
Estimates of sensitivity and specificity were not appreciably affected
by coding inadequate or missing screening test results as negative instead
of positive. Lastly, estimates of sensitivity and specificity for strategies
that included signal amplification prior to and after 2000 were not significantly
different (data not shown).
In this first US-based study comparing screening by thin-layer Pap smear
to screening by HPV DNA tests for detection of CIN 3 or higher, HPV DNA testing
was significantly more sensitive, but significantly less specific, than thin-layer
Pap testing. Compared with referring all women with abnormal smear results
for colposcopy, strategies that incorporated HPV DNA testing of ASCUS resulted
in significant improvements in specificity, with only slight decreases in
sensitivity. The strategy of requiring 2 positive PCR tests for HPV DNA was
both more sensitive and specific than referral of women with abnormal smear
results for colposcopy. All results were robust to differences in assumptions
regarding the definition of high-grade disease, age of the screening population,
and coding of missing or unsatisfactory screening test results.
Our uncorrected sensitivity estimates (for detection of CIN 2 or higher)
were generally similar to estimates presented in other studies.15 A
comparison of our results with those from a study of 2098 Canadian women (which
included referral of women with negative screening results)16 showed
similar corrected sensitivities for Pap tests (47.5% vs 40.2%) and for signal
amplification HPV DNA tests (71.4% vs 68.1%), but lower corrected specificity
estimates for Pap testing (82.9% vs 91.6%), and for signal amplification testing
(73.4% vs 90.6%). These differences may be due in part to the fact that, in
the Canadian study, biopsies were obtained at the discretion of the colposcopist,
women older than 50 years were included, conventional Pap smears were used,
and a less-sensitive signal amplification test was used for most of the study.
Overall, more women were positive for high-risk HPV DNA by signal amplification
(27.4%) than by PCR (18.3%). Although a similar proportion of women with HSIL
were positive by signal amplification and by PCR, more women with LSIL, ASCUS,
or normal cytology results were positive by signal amplification than by PCR.
One explanation for this difference is that the signal amplification test
for high-risk HPV types will detect the low- and indeterminate-risk types
that are frequently found in samples from women with normal, ASCUS, or LSIL
Pap results, but not in samples from women with HSIL.23- 25 Limiting
HPV testing to women aged 30 to 50 years resulted in improved specificity.
However, thin-layer Pap testing was also more specific, and both HPV testing
and thin-layer Pap testing were less sensitive in the older population. Due
to the age-related shift of the squamocolumnar junction from the ectocervix
to the endocervix, sample collection for both Pap and HPV DNA tests may be
more difficult among older vs younger women.
The characteristics of our population were similar to those of the population
enrolled in the ASCUS/LSIL Triage Study (ALTS),8 a
multicenter study of triage strategies for women with ASCUS or LSIL sponsored
by the National Institutes of Health. In particular, the CIN 3 or higher prevalence
among 401 women with ASCUS in our study was comparable to the CIN 3 or higher
prevalence reported for 1149 women with ASCUS enrolled in ALTS (5.2% vs 5.1%,
respectively), where histologic outcomes were determined by an expert pathology
Despite differences in age and ethnicity between our Planned Parenthood
population and the population of women from health maintenance organizations
studied by Manos et al,18 both studies showed
that testing of women with ASCUS for high-risk HPV DNA by signal amplification
was more sensitive for detection of CIN 2 or higher than was a repeat Pap
test showing ASCUS or higher. Our study extends these findings by showing
that, compared with referring all women with ASCUS to colposcopy, referring
only those with positive signal amplification test results achieved a significant
improvement in specificity, with only a slight loss in sensitivity. Whether
estimates of sensitivity and specificity for all of the 7 screening strategies
can be reproduced in older and less sexually active populations remains to
Our most serious potential limitation was low colposcopy attendance.
However, prior studies of screening in the United States have observed nonattendance
of 23% to more than 60%.26,27 In
our study, women who returned for colposcopy tended to have more severe Pap
smear findings and positive HPV test results. To address the potential bias
arising from differences in colposcopy attendance for women with different
test results, our estimates of sensitivity and specificity were corrected.
Importantly, while there were changes in the value of estimates after correction,
the overall conclusions did not change. Additionally, none of the women with
completely negative screening results who returned for colposcopy had CIN
3 or higher, suggesting that referral based on high-risk HPV DNA testing in
conjunction with thin-layer Pap testing identified most, if not all, women
with CIN 3 or higher, although our sample of women with completely negative
results was relatively small.
In our study, a higher percentage of women with abnormal Pap results
(72.7%) than women with positive HPV DNA results (67.9%) complied with recommended
follow-up. Schneider et al28 reported reversed
percentages, with 80.1% of women with positive HPV DNA tests and 61.9% of
women with abnormal cytology findings complying with recommended follow-up.
When a significant portion of a referred population fails to comply with follow-up,
it suggests that patients and/or their clinicians are uncertain as to the
significance of an abnormal or positive screening test result.29 Better
tests, clearer guidelines, and more education will help.
Cervical cancer screening practices are quite variable. In settings
where programs invite women to participate and virtually all women are screened
at regular intervals, the costs (psychological and monetary) of screening
with a less-specific test may outweigh the risk of delayed treatment associated
with use of a less-sensitive test. In settings where screening is more haphazard
than routine, or performed infrequently, screening with a highly sensitive
test provides greater reassurance that disease has not been missed in women
who screen negative.
In summary, a single HPV DNA test was more sensitive but less specific
for detection of CIN 3 or higher than any of the cytology-based strategies.
All screening strategies were somewhat less sensitive and significantly more
specific among women aged 30 years and older vs women younger than 30 years.
In some settings, screening for high-risk HPV DNA may be a reasonable alternative
to cytology-based screening.