REFRIGERATION OF BLOOD-SAMPLES PRIOR TO SEPARATION IS ESSENTIAL FOR THE ACCURATE DETERMINATION OF PLASMA OR SERUM ZINC CONCENTRATIONS

An evaluation of refrigeration (7 degrees C) to prevent falsely high p lasma or serum zinc concentrations owing to elapsed time between blood collection and centrifugation was performed. At room temperature (23 degrees C), both plasma and serum zinc concentrations increased signif icantly, if blood samples were stored uncentrifuged. Plasma zinc conce ntrations increased 6.3% at 1 h and 40.7% at 24 h, whereas serum zinc concentrations increased only 0.9% at 1 h and 12.5% at 24 h at room te mperature. When blood samples were stored uncentrifuged in the refrige rator for up to 24 h, there were no significant increases in zinc conc entrations in either plasma or serum. These findings suggest that plas ma or serum separation should be performed immediately after blood dra wing to obtain accurate zinc concentrations, and if this is not feasib le, the samples should be immediately refrigerated and separation perf ormed within eight hours.