Abstract
BackgroundThe study aim is to estimate sensitivity and specificity of anal cytology for histologic HSIL in analyses adjusted for the imperfect biopsy reference standard.Methods and Principal FindingsRetrospective cohort study of an anal dysplasia screening program for HIV infected adults. We estimated the prevalence of histologic HSIL by concurrent cytology category and the associated cytology ROC area. Cytology operating characteristics for HSIL were estimated and adjusted for the imperfect reference standard by 3 methodologies. The study cohort included 261 patients with 3 available measures: (1) referral cytology; (2) HRA cytology; and (3) HRA directed biopsy. The prevalence of biopsy HSIL varied according to the concurrent HRA cytology result: 64.5% for HSIL or ASC-H, 12.6% for LSIL, 10.9% for ASCUS, and 6.3% for no abnormality. The cytology ROC area was 0.78. The observed prevalence of HSIL was 37% (referral cytology), 24% (HRA cytology), and 24% (HRA biopsy). Unadjusted estimates of sensitivity and specificity of cytology were 0.66 and 0.90, respectively. Adjusted estimates varied from 0.47–0.89 (sensitivity) and 0.89—1.0 (specificity).ConclusionsAnalysis of a single dataset yields widely different estimates of anal cytology operating characteristics that depend on difficult to verify assumptions regarding the accuracy of the imperfect reference standard.
Highlights
In a systematic review dealing with screening HIV-infected individuals for precursors of anal cancer, Chiao et al reported that, among studies using similar methodology, the operating characteristics of anal cytological examination for high resolution anoscopy (HRA) directed biopsy varied from 69% to 93% and from 32% to 59% [1]
Analysis of a single dataset yields widely different estimates of anal cytology operating characteristics that depend on difficult to verify assumptions regarding the accuracy of the imperfect reference standard
Analyses will be restricted to the 261 patients with complete data on the 3 primary variables
Summary
In a systematic review dealing with screening HIV-infected individuals for precursors of anal cancer, Chiao et al reported that, among studies using similar methodology, the operating characteristics of anal cytological examination for high resolution anoscopy (HRA) directed biopsy varied from 69% to 93% (sensitivity) and from 32% to 59% (specificity) [1]. The low reported specificity implies a high false positive rate for cytology. This inference is flawed because it assumes that the reference standard, HRA-directed biopsy is a perfect gold standard that results in no misclassification of true disease status. Our study aim was to estimate the sensitivity and specificity of anal cytology for high grade anal dysplasia in analyses adjusted and unadjusted for the imperfect nature of the reference standard (HRA directed anal biopsy). The study aim is to estimate sensitivity and specificity of anal cytology for histologic HSIL in analyses adjusted for the imperfect biopsy reference standard
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