Evaluation of the Mythic 18 hematology analyzer for use with canine, feline, and equine samples

The Mythic 18 is a fully automated hematology bench-top analyzer using impedance technology for a complete blood cell count (CBC) and a 3-part white blood cell count (WBC) differential. The purpose of the current study was to evaluate the Mythic for assessment of agreement, precision, linearity, carry-over, stability, and usability under practice conditions. Ethylenediamine tetra-acetic acid-blood samples from 122 dogs, 140 cats, and 123 horses were analyzed with the Mythic and reference methods (Sysmex XT-2000iV, manual hematocrit, and microscopic WBC differentiation). Pearson's coefficient of correlation, Passing-Bablok regression analysis, and Bland-Altman difference plots were performed to determine agreement. For precision, standard deviation and coefficients of variation were calculated. Linearity was determined according to Emancipator-Kroll. Red blood cell parameters showed excellent correlation and small biases, except for red cell distribution width and mean corpuscular hemoglobin concentration. Total WBC correlated excellently in canine and equine and very well in feline samples. In 23 feline specimens with platelet aggregates, the Mythic overestimated WBC. In all 3 species, absolute granulocyte counts correlated excellently. Equine lymphocyte counts showed good correlation whereas canine and feline lymphocyte counts correlated poorly. Feline platelets showed good correlation with a negative bias. The instrument showed good to excellent precision. The whole 3-part differential was found to be accurate in horses. In dogs and cats, absolute granulocyte counts were reliable. As with all impedance-based hematological instruments, evaluation of a blood smear is absolutely indicated to check for the presence of platelet aggregates, to verify WBC differentiation, and to identify possible abnormalities.