Cervical Cytology and Histology Correlation as an Analytic Quality Assurance Exercise: Experience from an Accredited Cytology Laboratory

CONTEXT: The performance parameters of cervical cytology in any accredited cytology laboratory requires implementation of quality control exercise, which ensures acceptable performance by a laboratory. This study aims to assess the analytical aspect of quality control measures by evaluating the frequency and accuracy of epithelial abnormalities as detected in cervical Pap smears using histopathologic diagnosis as the gold standard. METHODS: A retrospective diagnostic test study from 2018 to 2020 was conducted. Out of the total 6000 Pap smears, histopathologic correlation was available in 150 cases in the form of colposcopic-directed biopsy (CDB) and loop electrosurgical excision procedure (LEEP) tissue in 105 cases. The quality control measures analyzed were Atypical Squamous Cell: Squamous Intraepithelial Lesion (ASC: SIL) ratio, cyto-histo correlation, and study parameters like sensitivity, specificity, positive predictive value, and negative predictive value of Pap smears as against CDB and LEEP. RESULTS: 4.5% smears were reported as inadequate, 92.3% as Negative for intraepithelial lesion or malignancy (NILM), followed by epithelial abnormality found in 3.21%. The ASC: SIL ratio was 1.3:1. Concordance rate against CDB was 100% in Squamous cell carcinoma (SCC), 82.35% in high-grade squamous intraepithelial lesion (HSIL), 82% in atypical squamous cells of undetermined significance (ASCUS), 65.6% in low-grade squamous intraepithelial lesion (LSIL), and 50% in Atypical Squamous Cell ,High grade Squamous Intraepithelial Lesion can not be ruled out (ASC-H). Total concordance rate was 84.15%. Sensitivity of Pap smear was 65% for LSIL and 82% for HSIL. Specificity, positive predictive value, and negative predictive value were 63.63%, 90%, and 75%, respectively. Concordance rate was 96% with LEEP. CONCLUSION: Quality control measures give an insight of performance of any accredited cytology laboratory. This exercise needs to be conducted on a regular basis, so that relevant steps can be taken in case of major discrepancy.