Number of Needle Passes Does Not Correlate with the Diagnostic Yield of Renal Fine Needle Aspiration Cytology

Background and Purpose: Renal Fine Needle Aspiration Cytology (FNAC) has gained popularity due to increasing options in management of renal lesions such as energy ablation and active surveillance. The diagnostic yield of renal FNAC varies between 40-90%. We hypothesized that adequate and diagnostic FNA samples would be associated with higher number of needle passes and higher number of slides examined. Patients and Methods: The pathology database at our institution was retrospectively searched for renal FNACs performed between 1995 and 2005. Patient gender, side, indication, cytological diagnosis, final histological diagnosis when available, number of needle passes performed, number of slides examined, and adequacy of the FNAC sample as determined by Diff Quik staining by the cytotechnologist (CS) were recorded. Chi square test was performed for statistical analysis. Results: Out of 377 renal biopsies performed, 259 were core biopsies for medical renal disease, and 118 were FNACs for renal lesions, including 16 for indeterminate complex renal cysts and 102 for solid renal masses. Indeterminate renal cysts were excluded from the study. Out of 102 FNACs for solid renal masses, 22 were inadequate with 13 (59%) being non-diagnostic; and 80 FNACs were adequate with 3 (4%) being non-diagnostic. The number of needle passes was not significantly different between non-diagnostic and diagnostic samples (2.5 vs 3.2); and between inadequate and adequate samples (3.4 vs 3.0). Similarly, the number of slides examined was not significantly different between non-diagnostic and diagnostic samples (9.5 vs 10.9); and between inadequate and adequate samples (11.3 vs 10.6). Diff Quik adequate samples had significantly higher diagnostic yields when compared to Diff Quik inadequate samples (965 vs 41%; p < 0.01). Conclusions: The number of needle passes and microscopic slides examined did not correlate with sample adequacy or diagnostic yield of renal FNAC. Sample adequacy as determined by Diff Quik staining correlated with diagnostic FNAC. Despite the retrospective nature of this study, a cytotechnologist should be present during the FNA procedure to ensure adequate samples have been obtained to increase the diagnostic yield of renal FNAC.