The clinical signs of copper (Cu) deficiency are largely non-specific and a number of laboratory tests have been used extensively to assist in diagnosis. Among these are whole blood, plasma and serum Cu and caeruloplasmin (McMurray, 1980). However, for any marker to be useful diagnostically, it is necessary to identify any factors which can affect it. Plasma and serum Cu are not equivalent but are related by the equation:
Serum Cu (mg/l) = 11.7 + 0.66 plasma Cu (mg/l). The regression was obtained from the means of 24 groups of suckler cows and calves (> 10 animals/group). The equivalent relationship between serum and plasma caeruloplasmin is:
Serum caeruloplasmin = 0.0018
+ 0.59 plasma caeruloplasmin.
Units of caeruloplasmin are absorbance units in the phenylene diamine assay.
Thus, the range of normality will depend on the sample being used for the assay. The reduction in serum values is due to the loss of caeruloplasmin during blood clotting.