A peculiar morphological alteration of canine neutrophils

Background: Multiple thin nuclear projections in canine blood neutrophils, here named “hairy”, have been anecdotally observed during routine hematology. A similar alteration has been described in people with hypercortisolism. Objective: To determine the analytical aspects of hairy neutrophils (HN) and their possible association with suspected hypercortisolism. Methods: Intra-observer repeatability and effects of stains were evaluated on both Hemacolor-stained smears (HSS) and May Grünwald-Giemsa-stained smears (MSS). Inter-observer repeatability was evaluated by two independent operators on HSS. The frequency of HNs and the possible association with suspected hypercortisolism was assessed on 223 HSS from dogs with normal (N=106) or high alkaline phosphatase (ALP) activity (N=117). Cohen’s K, Wilcoxon signed rank, and Spearman tests were performed to respectively evaluate concordance, differences between stains, operators or “ALP groups”, and correlations. Results: HNs were more visible on HSS, that provided higher counts than MSS, although without statistical significance. Intra-observer coefficient of variations ranged from 8 to 10% with higher values at low HN counts. Inter-operator concordance was good (k: 0.73). Results of the operators were significantly different (P=0.015) but correlated (p<0.001, r=0.625). HNs were detected on 74/223 cases (33.2%). The HN count was higher in dogs with high (58.2%) than in dogs with normal ALP (43.4%; P=<0.001) and in dogs with very high (3 X URL) (67.6%) than in dogs with high-normal ALP (48.1%, P=0.007). Conclusions: HN can be found in dogs, especially in HSS. Finding HN should prompt to measure ALP activity and, if high, to investigate the possible presence of hypercortisolism.