Analytic Errors in Hematology Results

Blood samples from a 14-year-old dog with marked leukocytosis with atypical cells were submitted to a diagnostic laboratory. Chronic T-cell lymphocytic leukemia (CLL) was diagnosed via blood smear evaluation and flow cytometric optic phenotyping. RBC count was higher by flow cytometry (RBC-O) than by electric impedance (RBC-I), which resulted in an ≈37% analytic error. RBC-I correlated well with the manual count. Overestimation of RBC-O may have been caused by incorrect classification of leukemic cells or fragments as reticulocytes, or pseudoreticulocytosis. The automated relative reticulocyte count was 35.3% as compared with a manual count of <1%.

Regarding packed cell volume, there was a 5% difference between manual packed cell volume and hematology analyzer hematocrit. RBCs appeared trapped in the buffy coat, which caused a pink hue in the separation area. Pseudoreticulocytosis, although not completely understood, must be considered when assessing the regenerative nature of anemia in canine CLL cases. However, hemoglobin concentration was not affected by cell-related artifacts and may be the best way to assess CLL-related anemia in dogs.

Commentary

Analytic errors in hematology testing might be detected by quality-control procedures performed by the laboratory technologist and/or analyzer software. This study highlighted the importance of carefully reviewing reported results and performing bedside tests to complement the CBC. Centrifugation of blood in microhematocrit tubes is helpful to confirm packed cell volume/total solids and to inspect the appearance of patient buffy coat and plasma color. Manual blood smear inspection allows verification of platelet number as well as detection of band neutrophils, platelet clumps, intracellular parasites, autoagglutination, toxic change, and changes in RBC conformation; thus, manual blood smear inspection greatly increases the diagnostic utility of a CBC. Without close inspection of hematology results, errors such as those in this report might be overlooked, which could delay diagnosis and proper treatment.—Julie Walker, DVM, DACVECC