Application of the International System for Reporting Serous Fluid Cytopathology to pericardial fluid: Root cause analysis of indeterminate diagnoses, cytohistological correlation, and assessment of malignancy risk

Abstract Background This study investigates the utility of the International System for Reporting Serous Fluid Cytopathology (ISRSFC) in the categorization of pericardial fluid and assesses the diagnostic performance and risk of malignancy (ROM) for each of the diagnostic categories. Methods All pericardial fluid cases at the Yale School of Medicine between January 1, 2017, and December 31, 2020, were reviewed. The diagnoses were reclassified into five categories according to the ISRSFC: nondiagnostic (ND), negative for malignancy (NFM), atypia of uncertain significance (AUS), suspicious for malignancy (SFM), and malignant (MAL). ROM and performance parameters of each category were calculated. Results After reclassification, the distribution of 465 pericardial fluid cases in each category was as follows: ND, 19 (4.1%); NFM, 332 (71.4%); AUS, 21 (4.5%); SFM, 11 (2.4%); and MAL, 82 (17.6%). Confirmatory follow‐ups were available for 16 ND (66.7%), 299 NFM (90%), 15 AUS (71%), 5 SFM (45.5%), and 30 MAL cases (36.6%). The ROM was 0% for ND, 1.3% for NFM (4 of 332), 20% for AUS (3 of 15), and 100% for both SFM (5 of 5) and MAL (27 of 27). The diagnostic performance was as follows: sensitivity, 87% (27 of 31); specificity, 100% (292 of 292); positive predictive value (PPV), 100% (27 of 27); negative predictive value (NPV), 98.6% (292 of 296); and diagnostic accuracy, 98.8% (319 of 323). Conclusions The ISRSFC is a highly useful system for the reporting of pericardial fluid and risk assessment, given that it offers high sensitivity, specificity, PPV, NPV, and diagnostic accuracy. The application of this system may help to better categorize pericardial fluid and facilitate the standardization of cytopathology reporting.