Abstract
BackgroundTo conduct a hematological analysis of avian blood samples, standard automated cell counting is unreliable because all avian blood cells are nucleated. Therefore, quantitative white blood cell counting in birds is still performed manually, whereby the Natt-Herrick method is widely used in veterinary laboratories. The aim of this study was to evaluate a new commercially available single test system for avian white blood cell counting, the Natt-Herricks-Tic®, which would allow easy in-house analysis by clinicians or technicians. A total of 40 avian ethylenediaminetetraacetic acid (EDTA) blood samples from 24 different species were included in the study. To assess method agreement, each blood sample was analyzed for total white blood cell count with the test method and the Natt-Herrick reference method. To determine the imprecision of the reference method and the Natt-Herricks-Tic® method, the noncorrected white blood cell count was determined ten consecutive times from one avian EDTA blood sample for each method.ResultsThe Natt-Herricks-Tic® method performed well concerning staining quality and countability of the granulocytes by the hemocytometer. In the agreement study, the Natt-Herricks-Tic® method showed a small proportional systematic error with a small positive mean bias of 282 white blood cells/μL but had wide 95% limits of agreement (− 4683 cells/μL to 5227 cells/μL), indicating random error. The precision study resulted in a coefficient of variation of 16% for the Natt-Herricks-Tic® method (the mean ± standard deviation: 9.7 × 103/μL ± 1.5 × 103/μL) and 23% (the mean ± standard deviation: 7.9 × 103/μL ± 1.8 × 103/μL) for the reference method.ConclusionsThe Natt-Herricks-Tic® method showed acceptable precision for a manual method and demonstrated good agreement with the reference method. It can be recommended as a reliable and suitable method for determining white blood cell counts in avian EDTA blood if nonstatistical quality control measures are used in the daily routine. The application of individual reference intervals for the interpretation of white blood cell counts in birds may improve the diagnostic performance of this important analyte in a clinical setting.
Highlights
To conduct a hematological analysis of avian blood samples, standard automated cell counting is unreliable because all avian blood cells are nucleated
Correlation between the white blood cell counts determined with the Natt-Herrick Tic® test method and the Natt-Herrick reference method revealed a correlation coefficient of 0.95
Regression analysis by Passing-Bablok method showed very small systematic error between the test method and the reference method: intercept, 412 White blood cell (WBC)/μL (95% confidence interval, 1.596 to 863); slope, 1.03 WBC/μL (95% confidence interval, 0.90 to 1.17) (Fig. 1)
Summary
To conduct a hematological analysis of avian blood samples, standard automated cell counting is unreliable because all avian blood cells are nucleated. In the author’s Laboratory a modification of the original Natt-Herrick protocol for avian WBC counting is in use for the last 25 years, which includes the counting of only the granulocyte population in the hemocytometer, followed by a manual blood smear differential of 200 WBC and adding the lymphocyte and monocyte counts to the granulocyte counts. With this technique, avian WBC count is easier to perform and much more reliable
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