Fluids--good and bad actors: observations from the College of American Pathologists Interlaboratory Comparison...

Body cavity fluid examination presents a common and sometimes difficult diagnostic challenge in daily cytology practice. Separating benign from malignant cellular changes may require meticulous screening, careful scrutiny of cellular features, and an understanding of the range of reactive changes. We use the data from the College of American Pathologists (CAP) Interlaboratory Comparison Program in Nongynecologic Cytology (NGC) to identify characteristics of fluids that place them at opposite ends of the diagnostic spectrum.

To assess the features of individual body cavity fluid slides that demonstrated good performance characteristics and compare them to slides that were poor performers.

A databank of 10 396 laboratory responses, including a variety of malignant and benign cases obtained from 1997 through 2001, was used to select cases. A cumulative slide history was used to identify slides that performed well or poorly in each reference diagnosis. Cases were confirmed by consensus of 4 CAP Cytopathology Resource Committee members. Observations and characterizations of good and bad performers in each category were recorded and summarized.

Percentage of concordance of poor performers ranged from 0% to 58%. Conversely, good performers were identified with high concordance of laboratory diagnosis in each reference category (>80%). Several patterns emerged. Poorly performing cases of adenocarcinoma consisted of slides with rare tumor cells, hypercellular malignant cases without 2 cell populations, and cases with single cells. Poor performance in confirmed squamous cell carcinoma cases related to rare cells without keratinization. Small cell carcinoma and melanoma cases performed poorly when there were few malignant cells. Lymphoma cases demonstrated poor performance when there were abundant pleomorphic lymphoid cells or when rare Reed- Sternberg-like cells were present. Reactive or negative slides performed best with a polymorphous population; poor performers were those with a predominant lymphocyte population mistaken for a hematopoietic neoplasm.

Close attention to classic cytologic criteria and careful examination of slides may enhance the educational experience of participants and the performance characteristics of body cavity fluid specimens in the CAP NGC program. Lessons from bad actors in the CAP NGC program may increase awareness of potential diagnostic problems in daily practice or help identify areas for laboratory quality improvement.