Analytic variability in the enumeration of neutrophil subpopulations in canine blood.

Background: Conventional differential leukocyte counts do not enumerate hyposegmented neutrophils (Hypo-PMN), ie, immature neutrophils that already lost the band morphology but are not yet completely segmented. They may be early indicators of acute inflammation.

Objectives: The purpose of the study was to evaluate the analytic variability of counts of segmented neutrophils (Seg-PMN), band neutrophils (Band), hyposegmented neutrophils (Hypo-PMN), non-Bands (Hypo-PMN + Seg-PMN), and Young-PMN (Bands + Hypo-PMN) assess if Hypo- or Young-PMN identify inflammation better than Bands.

Methods: Neutrophil subpopulations were counted by 2 observers on 2 sets of 100 cells in 267 blood smears from dogs with changes potentially consistent with inflammation to calculate the intra- and inter-observer variability.

Results: Median intra-observer CVs were < 5.0% for Seg-PMN and non-Bands, and 20.0% and 28.0% for Hypo-PMN and Young-PMN for observer 1 and 2, respectively; median inter-observer CVs for Seg-PMN, non-Bands, Hypo-PMN, and Young-PMN were 4.6%, 5.0%, 60.0%, and 47.1%, respectively. Median CV of Band counts in blood smears with bands was 141%.

Conclusions: The analytic variability of Hypo- and Young-PMN is lower than that of Bands. This retrospective study did not allow us to investigate the diagnostic potential or the clinical relevance of these cells. However, the low inter- and intra-observer variabilities with these cell populations suggest that the count of Hypo- or Young-PMN may better identify acute inflammation than the count of Bands.