Zinc deficiency is much more common than most GPs realise. But how does it present and how would you diagnose it?
Symptoms
A full blown case of zinc deficiency is quite a serious illness. In children it causes growth stunting and delayed sexual maturity, in adults dermatitis, alopecia and anaemia. Severe zinc deficiency is mainly a problem of third world countries.
A moderate form of the disease featuring hypogonadism and neurosensory changes has been reported in developed countries, but in Australian general practice it is much more likely that you will see marginal zinc deficiency. Symptoms of this milder deficiency state include: impaired taste, poor wound and ulcer healing and possibly impaired immune function.
Unfortunately most of these symptoms are quite non-specific and with a generally low level of awareness of the much zinc deficiency remains undiagnosed.
Tip: To improve your pick-up rate for zinc deficiency , recognise the high risk groups and risk factors, then act on suspicion.
Risk groups
The elderly and alcoholics (especially those with liver disease) are the two main groups at particular risk. Consider the diagnosis in hospitalised in-patients whose wounds are slow to heal. Vegetarians are also vulnerable to mild zinc deficiency (animal products are the main food source and zinc absorption is also impaired by a high phytate intake) but it is not clear that this is so important clinically.
In the history, anything which impairs dietary intake, particularly of animal foods, should add to your suspicions, particularly in the main risk groups and where there are possible symptoms of zinc deficiency.
Diagnosis
One of the main problems in making an accurate diagnosis of mild zinc deficiency is that there are no truly characteristic physical signs and no really sensitive laboratory indices. The principal lab test is the plasma zinc. It is more useful than the serum zinc and will pick up cases of marked deficiency. In one Australian study, 20% of community based and 30% of institutionalised elderly had low plasma zinc. Do not use a pressure cuff to collect the sample, as this can cause false elevation of the value. The OC pill depresses the values, but this does not appear to have any clinical significance. The main problem with this test, however, is that it is quite insensitive to marginal deficiency. Do NOT assume that a patient with `normal' plasma or serum zinc does not have zinc deficiency.
In an attempt to get around this limitation, nutritionists have tested other tissue samples.
Hair zinc has been widely used in research studies and is available in some Australian laboratories. However, it is easily affected by extraneous factors (such as hair shampoos) and its value in clinical practice is not yet established. For the future, it is possible that new tests such as ultrafiltrable zinc or serum alkaline phosphatase enzyme reactivation may assist with more sensitive diagnosis.
Summary
What should the GP do in practice to pick up cases of zinc deficiency? The reality is that you must rely to a considerable degree on your own clinical astuteness. Be sensitive to possible presenting symptoms, particularly when they occur in the elderly or alcoholic patient. Order a plasma zinc, but, where the clinical picture suggests the possibility of zinc deficiency, a short therapeutic trial of zinc supplementation will often be the most useful diagnostic approach. If symptoms improve, dietary modification will then form the basis of treatment.