Detection of low serum immunoglobulin concentrations in clinically ill calves

The sensitivity, specificity, and accuracy of classification of 4 tests for failure of passive transfer (FPT) were examined in clinically ill neonatal calves. Comparisons were made with serum IgG(1) concentrations determined by radial immunodiffusion. Serum samples were obtained from 27 clinically i ll calves less than or equal to 21 days of age. The results of 4 commonly u sed assays. the sodium sulfite turbidity test, the zinc sulfate turbidity t est, refractometry, and the serum gamma-glutamyl transferase (GGT) activity test, were compared with radial immunodiffusion determinations of serum Ig G(1) concentration. Serum GGT activity using a 50 IU/L threshold resulted i n correct classification of the highest percentage of calves (93%) with reg ard to their passive transfer status. The sodium sulfite test with a 1 + en d point and refractometry using a 5.5 g/dL end point resulted in correct cl assification of 85% of the calves studied. When using the sodium sulfite te st, the 2+ and 3+ test end points had lower specificity? 0.58 and 0.00, res pectively, than the 1 + end point. This loss in specificity resulted in mis classification of calves with adequate serum immunoglobulin concentrations as having FPT. The zinc sulfate turbidity test was inadequately specific (0 .33) and resulted in misclassification of 33% of calves.