Zinc (Blood)

Diagnostic Use

Zinc deficiency may occur in malabsorptive syndromes, patients receiving chronic total parenteral nutrition (TPN) solutions lacking adequate zinc supplementation, and with chronic diarrhoea, inflammatory bowel disease, or other conditions leading to increased zinc losses.  It may also occasionally occur in the context of malnutrition e.g. due to eating disorders.

Clinical manifestations include growth delay, delayed sexual maturation,  alopecia, change in hair colour, dysgeusia (impaired taste), immune dysfunction, night blindness, impaired wound healing, and various skin lesions. The dermatologic syndrome occurs primarily in the extremities or around body orifices and is often characterized by erythematous, vesiculobullous, and pustular lesions.

Since a wide range of foods including meat, fish, shellfish, nuts, seeds, legumes and whole-grain cereals are rich in zinc, deficiency does not occur in people who consume a balanced diet and have normal gastrointestinal function. Although vegetarians may be theoretically more likely to become deficient because zinc from plant sources is less bioavailable due to the presence of phytate which inhibits its absorption, in practice zinc deficiency is rare in vegetarians who have normal gastrointestinal function.

Acrodermatitis enteropathica is a very rare recessively inherited defect in intestinal zinc absorption. The clinical features include hyperpigmented skin lesions on the acral surfaces of the upper and lower extremities, as well as the face and buttocks. The rash usually appears in early infancy.

Occupational or environmental exposure is a rare cause of zinc toxicity.

Depression, chronic fatigue syndrome, autism etc:  A causal link between low plasma zinc and depression is not supported by convincing evidence. There is no value in measuring plasma zinc in patients with depression, chronic fatigue syndrome or autism spectrum disorder .

The clinical indication for testing must be written on the request form

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Interpretation

Low plasma zinc:

While zinc deficiency is rare, low plasma zinc levels are commonly seen in a wide range of conditions including infection, inflammation, malignancy, hypoproteinemia, stress, and pregnancy. It does not necessarily indicate zinc deficiency, or the need for supplementation, which should be assessed by clinical criteria.

Low plasma zinc in hypoproteinaemia :  As plasma zinc is 99% protein-bound, zinc levels will be low in hypoproteinaemic patients, without indicating zinc deficiency.   The formula below is used to calculate a “corrected zinc” level in hypoproteinaemic patients:

adjusted plasma zinc = plasma zinc  x   (73 / TP) where TP is total protein in g/L.

Acute phase reactions : plasma zinc may be up to 2 umol/L lower in patients with systemic inflammatory states (CRP >10 mg/L). This is due to the fact that the proteins to which zinc is bound decrease in inflammation.

Reference Intervals

Units : umol/L