Enhanced cellularity in plasma-thrombin cell block preparations: an improved method

Cell blocks are cytologic preparations that enable histologic evaluation and ancillary testing but are often limited by low cellularity. The plasma-thrombin method is widely used but can yield suboptimal cellular material.

We validated an improved plasma-thrombin method incorporating a second centrifugation step (1712 rpm, 10 min) after plasma and thrombin addition and the use of phloxine dye to enhance pellet visualization. Twenty paired body fluid samples were processed using standard and improved methods. Cellularity was quantified using digital image-based cell counting in the most cellular 20× field with the OnCellCounter platform; complete data were available for 18 paired cases and compared using the Wilcoxon signed-rank test. Following validation, the method was implemented hospital-wide. Adequacy (≥10 mesothelial cells, diagnostic atypia, or significant inflammation) was compared over 3-month periods before (June-August 2024) and after (April-June 2025) implementation using a Pearson χ² test.

In the validation cohort, the improved method showed higher cell counts in 12/18 (66.7%) cases, unchanged in 1/18 (5.6%), and lower in 5/18 (27.8%). Median cell count increased from 178 to 292 cells per 20× field (Wilcoxon P = 0.039), with complete diagnostic concordance. After implementation, adequacy improved from 56.5% (182/322) to 80.1% (277/346), an absolute increase of 23.5% (χ² = 42.98, P < 0.001).

Simple modifications to the plasma-thrombin method significantly improve cellularity and adequacy. This low-cost approach enhances diagnostic yield and may reduce repeat procedures.