Evaluation of fixation time using Diff‐Quik for staining of canine mast cell tumor aspirates

Abstract

Mast cell tumors are the most common cutaneous tumor in the dog and are often diagnosed via fine-needle aspiration and cytology. Many veterinary practices use Diff-Quik stain for these cases because it is easy to use and provides rapid results. Anecdotal reports suggest that Diff-Quik does not stain mast cell tumor granules well and that increased duration of fixation time can improve staining quality; however, this has not been prospectively evaluated. The aim of this study was to determine if varying fixation time would affect the staining quality of mast cell granules using the Diff-Quik stain. The null hypothesis was that there would be no difference in the staining of the granules based on duration of time in the fixation solution. Fine-needle aspirates of cutaneous mast cell tumors were obtained from 21 dogs and distributed on multiple slides. These slides were then stained in Diff-Quik at varying fixation times (ie, 5 seconds, 30 seconds, 1 minute, 2 minutes). One slide was stained with modified Wright stain as a control. Mast cell staining quality was evaluated either by blinded clinicopathologic review (n = 12) or by computer analysis of photomicrographs (n = 6). Results were compared with histopathologic grade. There was no difference in staining quality among groups. Alteration in fixation time using Diff-Quik does not improve staining characteristics of mast cell tumors.