The articles are definitely NOT for any public use whatever, nor intended in any way to be taken as advice for any medical or health condition.
The laboratory can be a powerful tool in confirming your nutritional diagnosis, but one that must be used with care. Laboratory testing tends to be less precise in nutrition than in many other fields of medicine, and there are no `routine screening tests' for nutritional status. The cost and lack of sensitivity of many nutrient assays means that the laboratory should only be used selectively to confirm a suspected deficiency, rather than taking a shotgun testing approach.
Many nutrients are hard to test accurately, because blood samples are not representative of the sites (such as enzyme systems, bone marrow etc.) where the nutrient is stored or acts. This can mean that a blood test remains normal even in deficiency states (example: plasma zinc), or that a mildly abnormal test result has little clinical meaning (example: vitamin B6 ).
To help solve this problem, tests have been devised to measure nutrients at the site where they act. For example, red cell folate assay. Other tests assess the functional effects of a nutrient deficiency, rather than measuring nutrient concentration directly. A common example is the measurement of haemoglobin to assess iron status (unfortunately not a very sensitive assessment). Another group of tests which uses this approach is red cell enzyme reactivation assays. They measure body status of certain nutrients (e.g. some of the B group vitamins) by testing how well a particular enzyme, which is dependant on the nutrient, is functioning in red cells.
Whatever test is used, check what foods and supplements the patient has been taking recently. Serum iron, for instance, is strongly influenced by the iron content of recent meals. Vitamin C supplements can lower serum B12 levels. However, in most cases fasting samples are not required for nutrient testing.
Many laboratories now offer red cell reactivation tests are available for certain of the B group vitamins: thiamin (TPP reactivation test), riboflavin (GRAC reactivation) pyridoxine (SGOT reactivation). Of these, SGOT reactivation has proved of limited clinical use as it is hard to interpret clinically.
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