Quantitative assessment of spray vs immersion fixation for thyroid fine-needle aspiration specimens

Whether spray or immersion fixation results in higher adequacy rates for thyroid fine-needle aspiration is not known. I compared 1-year adequacy rates, number of cells, and atypia rates for immersion fixation with split spray fixation and immersion. Adequacy rates increased from 71.9% (289/402) for complete immersion to 78.1% (332/425) with spray fixation of half of the slides (P = .02). The spray-fixed slides had an average + or - SD of 49.7 + or - 47.5 cells compared with their paired immersed slides, with 25.4 + or - 36.8 cells (96% more cells for spray fix; P < .001). Of the 402 immersion cases, 10 (2.5%) were diagnosed as atypical related to preparation artifact compared with 14 (3.3%) of cases with split preparation (P = .48). Spray fixation results in 96% more follicular cells in scant thyroid aspirates than immersion fixation and a significant increase in adequate aspirates without a significant increase in the atypia rate related to preparation.