Performance of red blood cell indices for the detection of reticulocytosis in anemic and non-anemic dogs in Taiwan

Reticulocyte counts (RETIC) are considered the gold standard in detecting an erythroid bone marrow response (BMR) in anemic and non-anemic dogs. Reticulocytosis without anemia (RWA) is a potential indicator of disease. The prevalence of anemia or RWA, as well as the effectiveness of red blood cell (RBC) indices in identifying a BMR, may vary based on geographical locations and breed differences. The purpose of the study was to determine the prevalence of regenerative and nonregenerative anemia, and RWA in pet dogs of Taiwan, and to assess the sensitivity and specificity of combined increased mean cell volume and decreased mean cell hemoglobin concentration (iMCV+dMCHC) to detect reticulocytosis in this population. The final population analysis consisted of 149,076 dogs. A cross sectional, retrospective analysis of complete blood count (CBC) samples from a field of automated hematology analyzers in Taiwan from December 1, 2018 through December 31, 2020 was performed. Among 149,076 dogs, 11.8 % (n=17,600) had reticulocytosis (RETIC > 110K/µl) and 21.8 % (n=32,474) had anemia (HCT < 37.3 %). Of 32,474 anemic dogs, 17.8 % (n=5,789) had reticulocytosis. Of 116,602 dogs without anemia, 10.1 % (n=11,776) had reticulocytosis. Across all dogs, sensitivity/specificity of iMCV+dMCHC to detect BMR was 4.3 % and 99.4 %, respectively compared to RETIC. Among anemic dogs, sensitivity/specificity of iMCV+dMCHC to detect BMR was 9.8 % and 99.2 %, respectively. Among non-anemic dogs, sensitivity/specificity of iMCV+dMCHC to detect BMR was 1.6 % and 99.5 %, respectively. Therefore, most regenerative anemias and cases of RWA did not have a combined iMCV+dMCHC. To avoid overlooking potential illness, RETIC should be evaluated regardless of whether patients have anemia or not.