Comparative evaluation of collodion bag and HistoGel cell block techniques in effusion cytology: a prospective study of 117 specimens

INTRODUCTION: Cell block (CB) preparation enhances morphological evaluation and enables ancillary testing in effusion cytology. Although HistoGel is widely used, the collodion bag method has been historically recognized for improved cellular recovery but remains underutilized. This study aimed to compare the diagnostic performance, technical quality, reproducibility, and downstream utility of the collodion bag and HistoGel CB methods. MATERIALS AND METHODS: A prospective cross-sectional study was conducted on 117 effusion specimens. Samples were processed in parallel using collodion bag and HistoGel methods. Slides were independently scored by 3 pathologists using a five-parameter system. Paired comparisons were performed using the Wilcoxon signed-rank test. Interobserver agreement was assessed using intraclass correlation coefficients (ICCs). DNA yield was analyzed in 25 paired cases. RESULTS: The collodion bag method yielded significantly higher scores for artifact reduction (P= 0.0058), tissue contamination (P= 0.0280), cell distribution (P< 0.0001), and tumor burden (P< 0.0001). No significant difference was observed in cell preservation. Interobserver agreement was good for tumor burden (ICC = 0.789) and moderate for total score (ICC = 0.587). DNA concentration was higher in the collodion bag method compared with HistoGel (31.5 versus 28.3 ng/μL, P= 0.048), with a median paired difference of 7.1 ng/μL. The collodion bag method required longer preparation time but only slightly higher material cost. CONCLUSIONS: The collodion bag method provides improved morphologic quality and higher DNA yield compared with the HistoGel method, supporting its utility in optimizing CB preparation, particularly for cases requiring ancillary and molecular testing.