Study on biological variability of haematological components in dogs
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The aim of the present study was to estimate the between-dog, within-dog and analytical components of variance for red blood cell (RBC) concentration, white blood cell (WBC) concentration, haematocrit (HT) and haemoglobin (HGB) in clinically healthy dogs and to use these estimates to calculate the critical difference for significance between serial results, to assess the utility of the conventional population-based reference intervals, and to set desirable performance standards for the analytical imprecision. RBC, WBC, HCT and HGB were measured in duplicate in blood samples collected monthly for 10 consecutive months from 23 clinically healthy dogs and the test results were subjected to nested analysis of variance. For RBC, the between-dog variation was 4.4%, the within-dog variation was 5.4%, the analytical variation was 2.8%, the critical difference was 17%, the index of individuality was 1.38 and the maximum allowable analytical imprecision was 2.7%. For WBC, the values were 12.3%, 12.1%, 3.7%, 35%, 1.03 and 6.1%. For HCT, the values were 5.2%, 6.4%, 1.1%, 18%, 1.25 and 3.2%, and for HGB, the values were 4.7%, 5.9%, 2.9%, 18%, 1.40, and 3%.
In practical terms, the present study indicates that the analytical imprecision of RBC, HCT and HGB should be below 3% and below 6% for WBC. Single measurements of RBC, HCT, HGB, and to a lesser extent WBC, in single dogs can be compared usefully to the corresponding reference intervals. The critical differences expressing the difference needed between two serial test results from the same dog to be significant at a 5% level was about 18% for RBC, HCT and HGB, and 35% for WBC.
KeywordsAnalytical variance Canine Inprecision
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