Observer reliability and components of variance in counting spherocytes in canine blood samples

Spherocytosis is an important component in the diagnosis of immune-mediated haemolytic anaemia (IMHA) in dogs. Information on variation due to counting and observer reliability in enumeration of spherocytes is limited. This study investigated the observer reliability of spherocyte enumeration, the within- and between-day variation due to counting, and the occurrence of spherocytes among anaemic and non-anaemic dogs. Within-and between-day variation was generally good to excellent for samples with five or more spherocytes per high power field (HPF; 1000 ×). Observer variation was generally high but the associated 95 % confidence limits indicated the importance of experience in detecting spherocytes. The upper 95th percentile of spherocytes among non-anaemic dogs was 2.63 spherocytes per HPF, and up to 3.78 among anaemic dogs without IMHA reflecting that spherocytes are not pathognomonic for IMHA but can be seen in other situations as well, most often in lower numbers than the limit of ≥ 5 spherocytes/HPF typically used in the diagnosis of IMHA.