There is no single laboratory test that adequately measures zinc nutritional status.
The best method of accurately determining zinc
status is through measuring white blood cell
levels. Since this test is not readily available and may be more expensive, serum zinc is routinely used as a screening tool.
Hair levels may show deficiencies or excesses but are generally not considered as reliable as other tests of zinc status. While low hair zinc is likely to be indicative of poor zinc status, elevated hair zinc may be indicative of low zinc in the cells or contamination from the use of zinc-containing shampoos.
The zinc taste test
appears to be of some value in determining general zinc status. The test is based on the knowledge that the functions of taste and smell are dependent upon there being sufficient zinc available in the body. Thus, if zinc is deficient then taste function will be diminished. This principle is utilised in the taste test by offering a standard test solution of zinc sulphate for tasting. The response is then compared with a series of defined standards and the zinc status thus determined.
This simple, non-toxic zinc taste test
uses a test solution of zinc
sulphate in purified water, at a concentration of 1gm/liter. Once prepared, the solution should be stored in a refrigerator and discarded after six months. The solution should be removed from storage and left at room temperature for about two hours before carrying out the test. The test involves taking a sip of the solution (approximately 5-10ml) and holding it in the mouth exactly ten seconds. Due to the possible influence of recently consumed food or drink on the taste experienced, it is essential that neither be taken for approximately one hour before the test.
For the zinc taste test
, the defined standards are:
- Grade one response: no specific taste sensation: tastes like plain water. This indicates a major deficiency of zinc requiring a supplement of at least 150mg of zinc per day.
- Grade two response: no immediate taste is noticed but, within the ten seconds of the test, a 'dry' or 'metallic' taste is experienced. This indicates a moderate deficiency requiring a supplement of 100mg of zinc per day.
- Grade three response: an immediate slight taste is noted, which increases with time over the ten second period. This indicates a deficiency of minor degree requiring a supplement of 50mg per day.
- Grade four response: an immediate, strong and unpleasant taste is experienced. This indicates that no zinc deficiency exists. If this is the response to the first test done then obviously the diet already contains sufficient zinc and no supplement need be taken. If this is the response, however, after a period of zinc supplementation then the diet, prior to the supplement being given, must be assumed to have been deficient. Thus, if a relapse to this deficient state is to be further prevented a regular maintenance dose of zinc is required. One 15-20mg dose per day is usually sufficient for this purpose.