There is no reliable method of assessing zinc stores. Suspected zinc deficiency can best be tested by monitoring the symptomatic response to the administration of zinc.
A change in plasma zinc does not occur until zinc intake is extremely low. Only 10 to 20% of the zinc in blood is contained in the plasma. Most is bound to alpha2-macroglobulins or to albumin. Hypoproteinemia or hyperproteinemia can alter plasma zinc levels. Other factors that influence plasma zinc are stress, infection, and hormones. Plasma zinc is useful for assessment only if the effect of poor zinc status can be differentiated from these conditions.
This test measures the change in plasma zinc after zinc is orally administered. A normal response is a doubling of plasma zinc peaking at three hours, though the test is quite variable among subjects.
Hair zinc levels of less than 70 mcg per gram (gm) have been associated with clinical signs of marginal zinc deficiency, such as impaired growth and poor appetite, in children. Hair zinc measurements cannot be used in severe malnutrition because of a decrease in the rate of hair growth in malnourished patients.
Decreased taste acuity is a symptom of zinc deficiency in both children and adults. In a taste acuity test, solutions of varying concentrations of the four different taste qualities (salt, sweet, bitter, and sour) are used. The test is based on the detection and recognition thresholds for each taste quality.