Performance Characteristics of Body Fluid Cytology Analysis of 344 380 Responses From the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology.

CONTEXT: - Body fluid cytology is an important diagnostic tool used to identify various conditions. However, an accurate diagnosis in this setting can sometimes be challenging. OBJECTIVE: - To identify the performance characteristics of body fluid cytology by analyzing participant responses from the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology. DESIGN: - Participant responses from 5102 slides were analyzed for concordance to the general category (GC) and to the reference diagnosis (RD). Nonlinear mixed models were used to analyze concordance. RESULTS: - The overall GC concordance was 95.2%. The GC type, participant type, and preparation type were significantly associated with GC concordance ( P < .001). Concordance for malignant cases was higher than it was for benign cases. Cytotechnologists had better GC concordance compared to pathologists. ThinPrep (Hologic, Marlborough, Massachusetts) slides had the highest GC concordance. Participant type, fluid type, preparation type, and participant interpretation were significantly associated with RD concordance ( P < .001). Pathologists performed better than cytotechnologists did for RD concordance. Pericardial fluid had the lowest RD concordance, especially for cases with normal or reactive findings. Modified Giemsa-stained slides performed best for lymphoma and hematopoietic malignancy. Small cell carcinoma had the highest GC concordance, and its RD concordance was higher in pleural than in peritoneal fluids. Adenocarcinoma showed the highest concordance rates for both GC and RD. CONCLUSIONS: - This study illustrates the challenges associated with interpreting body fluid cytology, particularly in pericardial fluid, and the factors that may affect accurate diagnoses. The results also highlight the value of using multiple preparation types in challenging cases.