Critical Difference of Some Bovine Haematological Parameters

Abstract

The purpose of the present study was to calculate the critical difference between 2 analytical results for the red blood cell count (RBC), the white blood cell count (WBC), the haemoglobin concentration (Hb), and the haematocrit (PCV) in blood from Red Danish Dairy cows. The critical difference can help to judge whether the difference between 2 consecutive analytical results from the same animal may be safely ascribed to natural variation or not.

To calculate the critical differences, blood samples from 20 clinically healthy lactating cows were collected once daily for 5 consecutive days. The total variance of the analytical results was divided into the component of variance between cows (S ²_Inter ), the component of variance for days within cows (S ²_Intra ), and the component of variance for measurements (S ²_Anal ) using nested analysis of variance. The critical difference was then calculated from S ²_Intra and S ²_Anal as 0.61×10¹²/l for RBC, 2.2×l0⁹/l for WBC, 0.79 mmol/1 for Hb, and 0.07 for PCV.

The critical differences may be used as guidelines to indicate potentially important changes in the parameters. However, the analytical results should not be assessed by the critical differences alone, but should also be compared to the corresponding reference intervals.

Sammendrag

Formålet med nærværende undersøgelse var at beregne den kritiske differens mellem to analytiske resultater for erythrocyttallet (RBC), det totale leukocyttal (WBC), hæmoglobinindholdet (Hb) og hæmatokrit (PCV) hos kvæg. Ved bestemmelse af den kritiske differens bliver det muligt med rimelig sikkerhed at afgøre, om en ændring af den målte parameters værdi enten kan skyldes rene tilfældigheder eller ej. Der udtoges blodprøver fra 20 lakterende kvæg af Rød Dansk Malkerace en gang dagligt 5 dage i træk. Ved hjælp af hierarkisk variansa- nalyse beregnedes den inter-individuelle, den intraindividuelle og den analytiske variation, og på basis af dette beregnedes den kritiske differens for de analyserede hæmatologiske parametre. I absolutte tal beregnedes den kritiske differens som værende 0,61×l0¹²/l for RBC, 2,2×10⁹/l for WBC, 0,79 mmol/l for Hb og 0,07 for PCV De beregnede kritiske differencer bør dog kun anvendes som vejledende værdier. Analyseresultater bør derfor ikke bedømmes alene ved hjælp af de beregnede kritiske differenser, men bør også bedømmes i forhold til de respektive reference intervaller.