A liquid concept--do classic preparations of body cavity fluid perform differently than ThinPrep cases? Observations from the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology.

Context: Newer liquid-based preparations differ morphologically from classic preparations (smears, filters, and cytocentrifuged preparations). Is adenocarcinoma more readily detected in liquid-based preparations? We reviewed responses from 16,750 fluid challenges of adenocarcinoma distributed in 2005 in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology (CAP NGC).

Objective: To compare the performance of body cavity fluid liquid-based preparations with adenocarcinoma to that in classic preparations in the CAP NGC.

Design: Responses for ThinPrep challenges were compared with classic preparations for exact match diagnoses of adenocarcinoma from pelvic washes, pleural fluid, pericardial fluid, and peritoneal fluids in the 2005 CAP NGC.

Results: A total of 13,690 pathologists, 8345 cytotechnologists, and 5958 laboratories submitted responses to fluid challenges in 2005. Adenocarcinoma comprised 16,750 of the fluid challenges; 88% were classic preparations, and 12% were ThinPrep challenges. The exact match to the reference diagnosis of adenocarcinoma was seen in 77% of conventional preparations and 81% of ThinPrep challenges when a general category of "positive for malignancy" was assigned. When "suspicious for malignancy," an exact match diagnosis of adenocarcinoma was made in 5% and 4% of classic and ThinPrep challenges, respectively.

Conclusions: ThinPrep challenges performed slightly better overall, but only pelvic washings and peritoneal fluids demonstrated statistically significant improved performance with ThinPrep challenges. Use of liquid-based preparation is widespread for nongynecologic preparations and performs as well, and sometimes better than, classic preparations in an interlaboratory comparison program.