Abstract
This chapter reviews the evidence indicative of a relative vitamin B6 deficiency in pregnancy and in some patients with miscellaneous diseases. Evidence for the presence of a relative vitamin B6 deficiency in pregnancy and various other conditions is based exclusively on laboratory examinations. Tests that are useful in the valuation of vitamin B6 metabolism include those concerned with the urinary excretion of intermediary metabolites following oral adminostration of tryptophan, preferably before and after the administration of pyridoxine. The blood levels of other vitamin B6-dependent enzymes—for example, serum glutamine-oxalacetic transaminase—can also give information as to the availability of vitamin B6 in clinical subjects. Similarly, the urinary excretion of 4-pyridoxic acid can be used to judge the amount of metabolized vitamin B6. Measurements of the total B6 content and its enzymatically active fractions, pyridoxal phosphate and pyridoxamine phosphate, in various components of the circulating blood will reflect the amount of available vitamin B6 in the body.
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