Description
Vitamin B6 is a water-soluble vitamin and is part of the vitamin B complex group. Pyridoxal phosphate (PLP) is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation. PLP also is necessary for the enzymatic reaction governing the release of glucose from glycogen.
Pyridoxal phosphate, the metabolically active form of vitamin B6, is involved in many aspects of macronutrient metabolism, neurotransmitter synthesis, histamine synthesis, hemoglobin synthesis and function and gene expression. Pyridoxal phosphate generally serves as a coenzyme for many reactions and can help facilitate decarboxylation, transamination, racemization, elimination, replacement and beta-group interconversion reactions.
The liver is the site for vitamin B6 metabolism.
Its concentration is measured by means of analysis of a blood sample drawn from the vein in the arm.
Purpose of the test
Determining vitamin B(6) status in persons who present progressive nerve compression disorders, such as carpal tunnel and tarsal tunnel syndromes.
Determining the overall success of a vitamin B(6) supplementation program.
Diagnosis and evaluation of hypophosphatasia.
Reference range values
5.0-30.0 ng/mL
Abnormal findings
The classic clinical syndrome for B6 deficiency is a seborrhoeic dermatitis-like eruption, atrophic glossitis with ulceration, angular cheilitis, conjunctivitis, intertrigo, and neurologic symptoms of somnolence, confusion, and neuropathy.
While severe vitamin B6 deficiency results in dermatologic and neurologic changes, less severe cases present with metabolic lesions associated with insufficient acitivities of the coenzyme pyridoxal phosphate. The most prominent of the lesions is due to impaired tryptophan-niacin conversion. This can be detected based on urinary excretion of xanthurenic acid after an oral tryptophan load. Vitamin B6 deficiency can also result from impaired transsulfuration of methionine to cysteine. The pyridoxal phosphate-dependent transaminases and glycogen phosphorylase provide the vitamin with its role in gluconeogenesis, so deprivation of vitamin B6 results in impaired glucose tolerance.
A deficiency of vitamin B6 alone is relatively uncommon and often occurs in association with other vitamins of the B complex. The elderly and alcoholics have an increased risk of vitamin B6 deficiency, as well as other micronutrient deficiencies. Renal patients undergoing dialysis may experience vitamin B6 deficiency. The availability of vitamin B6 to the body can be affected by certain drugs such as anticonvulsants and corticosteriods.