Plasma and serum zinc concentrations: effect of time between collection and separation

The effect of time between collection and separation of blood samples obtained from 9 subjects was examined with respect to plasma and serum zinc concentrations. There was a linear increase of 6% in zinc concentrations for the first 2 h that was similar for plasma and serum. Plasma zinc continued to increase linearly over the next 2 h, but increase in serum zinc concentrations was less for the second 2 h. It is concluded that differences between heparinized plasma and serum zinc concentration observed previously in this laboratory and elsewhere are attributable primarily to differences in time between collection and separation.