Is plasma zinc a useful investigation?

Plasma zinc is totally protein bound and its concentration is markedly influenced by alteration in protein concentration. Venous occlusion such as is used prior to venepuncture causes a marked increase in plasma zinc concentration. The extent of this change exceeds the analytical variation for zinc determination and may cause difficulty in the interpretation of plasma values. Although in most individuals there is a close correlation between plasma zinc and total protein, collectively this is not so, thus adjusting zinc values for change in protein is inappropriate. For plasma zinc to be a useful investigation blood samples should be obtained without venous occlusion.