Comparison of digital and optical microscopy for the evaluation of veterinary blood films: a preliminary study

Digital microscopy is increasingly used in veterinary diagnostic pathology. However, limited independent research has been published on its use, especially for the purpose of evaluating blood films. Hence, determining the potential limits of blood film assessments obtained via digital microscopy is needed. We compared the agreement of digital and optical cytology for the detection of common cellular morphology changes and abnormalities in veterinary blood films. Twenty-two veterinary clinical pathologists and residents evaluated canine, feline, and equine blood films on glass slides via optical microscopy and digitized blood film slides, with a ≥8-wk washout period between evaluations. One of the equine cases was a patient experimentally infected with Theileria haneyi. Using a standardized rubric, 16 erythrocyte features, 2 platelet features, and 2 leukocyte features were scored from absent to 4+. Additional comments at pathologist discretion were recorded. Changes in erythrocyte shape, platelets, and leukocytes were readily identified on both digital and glass slides. T. haneyi organisms were identified on significantly fewer digitized blood film slides than glass slides. Additionally, intra-observer consistency was low between digitized blood film slide and glass slide evaluation. Relative to glass slides, digitized blood film slides appear generally adequate for identifying erythrocyte, leukocyte, and platelet morphology changes, but may be inadequate for identifying intracellular T. haneyi organisms; however, more studies are needed. Clinicians should exercise caution when interpreting results from digitized blood film slides in which blood-borne infectious disease may be present.