Intra‐ and inter‐rater agreement for the detection of band neutrophils and toxic change in horses

Background The detection of band neutrophils and toxic change via microscopic blood smear review is vitally important, as their presence indicates systemic inflammation. However, in‐clinic evaluation of WBC morphology is often limited. Objective We aimed to determine the agreement between expert raters in the detection of bands and toxic change. Methods Three board‐certified clinical pathologists each evaluated 109 blood smears from horses with acute disease, and 19 control smears from healthy horses. The pathologists determined if bands were present, and if so, the percentage of bands present. They also determined if toxic change was present, and if so, the grade of toxic change. Intra‐rater agreement was evaluated using 12 duplicate blood smears. Agreement on the presence of bands between pathologists and an in‐clinic hematology analyzer was evaluated. Results Intra‐rater agreement was substantial to almost perfect. Agreement between pathologists for the detection of bands was moderate, but when pathologists agreed bands were present, there was excellent agreement on the percentage of bands and mature neutrophils. Agreement between pathologists for the detection of high‐grade, clinically relevant toxic change was fair. When pathologists agreed high‐grade toxic change was present, there was fair agreement on Döhle bodies and cytoplasmic basophilia and poor agreement on cytoplasmic vacuolation. Agreement between individual pathologists and the in‐clinic hematology analyzer for the indication of bands was fair to moderate. Conclusions Consistent identification of bands and toxic change is challenging, even for highly trained personnel. It is, thus,not surprising that in‐clinic blood smear evaluation of WBC morphology by non‐experts could be inadequate.