Accuracy of conventional cytology: results from a multicentre screening study in India

Abstract

Objective: We conducted a multi-centre cross-sectional study in India to evaluate the accuracy of conventional cytology to detect high-grade squamous intraepithelial lesions (HSIL). Setting: Cross-sectional studies in Jaipur, Kolkata, Mumbai and Trivandrum, India, during 1999-2003. Methods: A common protocol and questionnaire were used to test 22,663 women aged 25-65 years with conventional cytology in five cross-sectional studies. Three thresholds were used to define test positivity: atypical squamous cells of uncertain significance (ASCUS), low-grade squamous intra-epithelial lesion (LSIL), or HSIL. All screened women were investigated with colposcopy, and biopsies were taken when necessary. The reference standard for final disease status was histology or negative colposcopy. Data from the studies were pooled to evaluate the test characteristics for the detection of histologically confirmed HSIL. Results: The test positivity rates of cytology were 8.8% at ASCUS, 6.2% at LSIL and 1.8% at HSIL thresholds, and 355 women had histologically confirmed HSIL while 74 had invasive cancer. The pooled sensitivity, specificity, positive and negative predictive values at ASCUS threshold were 64.5%, 92.3%, 11.8% and 99.4% respectively. The corresponding values at LSIL threshold were 58.0%, 94.9%, 15.2% and 99.3%, while at the HSIL threshold they were 45.4%, 99.2%, 46.3% and 99.1%. The sensitivity varied between 37.8-81.3% at ASCUS , 28.9-76.9% at LSIL and 24.4-72.3% at HSIL thresholds. A significantly low sensitivity was observed in women aged 25-39 years (p<0.001). The wide variation in sensitivity across study sites persisted even after age standardisation. Conclusion: The sensitivity of cytology varied widely between the study sites. Findings from our study and other reviews indicate that sustained efforts in improving sampling, preparation and reading of cytological specimens and improvements in clinical judgement are essential to achieve concurrently high sensitivity and specificity.