Laboratory performance measures: evidence against low-risk women explaining low detection rates of high-grade abnormalities.
OBJECTIVE
When a laboratory has a low reporting rate of high-grade abnormality for its cervical cytology specimens, the question arises whether this is due to the laboratory screening a low-risk group of women. This study was undertaken to explore the hypothesis that a low-risk group of women were screened by Victorian laboratories not meeting the recommended minimum standard for the detection of high-grade abnormalities.


METHODS
A cohort of 28 094 women was established comprising women whose cervical cytology was reported in 2000 by laboratories not meeting the recommended standard of 0.5% high-grade abnormalities in their reporting of community smears. Outcome measures included the prevalence of high-grade abnormality on the next cytology test for the women, the positive predictive value of the cytology reports of high-grade abnormality, and the standardized incidence ratio for a later diagnosis of cervical cancer.


RESULTS
The prevalence of high-grade abnormality was 0.36% on the index cytology compared with 0.68% on the first subsequent cytology report. Sixty-nine per cent (60/87) of the index cytology reports of high-grade abnormality were confirmed as high-grade abnormalities on histology, compared with 70.8% (121/171) for the first subsequent reports of high-grade abnormality. During 70 015 person-years at risk, nine cases of cervical cancer were observed compared with 5.21 expected cases, giving a standardized incidence ratio of 1.73 (95% CI 0.79-3.28).


CONCLUSIONS
These results do not support a hypothesis that the low detection rate for high-grade abnormalities is due to the women comprising a low-risk group for cervical neoplasia.
Mitchell
H S
HS
Victorian Cervical Cytology Registry, Carlton South, Vic., Australia. heather.mitchell@vccr.org
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008403:Mass Screening; D008875:Middle Aged; D011237:Predictive Value of Tests; D012307:Risk Factors; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis* / Q000473:pathology; D014626:Vaginal Smears / Q000592:standards