How adequate is plasma zinc as an indicator of zinc status?

Determination of plasma zinc is the most widely used parameter for assessing the body status of this trace element. Plasma zinc levels are influenced by a wide variety of conditions, including infections and other factors causing stress. Low plasma zinc levels are not always indicative of zinc deficiency. Liver zinc is a much better parameter than plasma zinc for assessing subclinical deficiencies induced by dietary factors or disease. When the plasma zinc level is reduced, there is a reciprocal increase in plasma copper, and as such the copper:zinc ratio in plasma may reflect the temporary shift in plasma zinc. Whenever possible, plasma zinc level determinations should be complemented with zinc concentration determinations in a nucleated tissue, such as liver, muscle or bone. Zinc-dependent enzymes may not always reflect the status of the element in the body. In summary, then, plasma levels of zinc alone cannot be regarded as definitive evidence for assessing the body status or deficiency states of zinc.