Clinical Use: To assess a patients Vitamin B6 status and determine if they are deficient or have increased levels which may become toxic.
Background: Vitamin B6 is a water soluble vitamin which comprises pyridoxine, pyridoxal and their 5-phosphate esters. Vitamin B6 is widely distributed in food and is dephosphorylated by alkaline phosphatase in the gut for absorption. Following absorption ATP dependent phosphorylation restores phosphate ester forms. Vitamin B2 dependent oxidases oxidise pyridoxine 5-phosphate and pyridoxamine 5-phosphate to pyridoxal 5-phosphate (PLP) which is the active coenzyme form of Vitamin B6. Measurement of PLP and its precursor (pyridoxal) are used to assess vitamin B6 status. Vitamin B6 is important for many metabolic reactions, particularly serotonin and tryptophan formation. Vitamin B6 is an essential cofactor for aminotransferase enzymes. Deficiency may occur in the diet, due to drugs such as isoniazid and penicillamine, and as an inborn error.

Deficiency of Vitamin B6 leads to increased homocysteine levels. Iron absorption is also compromised.

Symptoms of deficiency include: – Skin changes (scaling, hyperpigmentation), inflammation of tongue, depression and irritability.

Use of mega dose Vitamin B6 (up to 6000mg/day compared with a reference nutrient intake several order of magnitude lower) has been described eg. Cystathionase deficiency.

Type 1 primary hyperoxaluria (AGT enzyme needs Vitamin B6 as cofactor), Idiopathic carpal tunnel, PMT, Schizophrenia, Autism

Vit B6 toxicity results in peripheral neuropathy and encephalopathy. Elevated Vitamin B6 may be seen with hypophosphatasia (low alkaline phosphatase). Clinical manifestations include defective skeletal mineralisation resulting in osteomalacia/rickets, and dental problems

Reference Ranges: Adult: 40 – 100 nmol/L
Associated Diseases:
Patient Preparation: None required
Specimen Requirements: EDTA – Whole Blood
Turnaround Time: 2 weeks
Additional Information: Persistently raised pyridoxyal phosphate (Vitamin B6) can be associated with peripheral neuropathy. Consider also possibility of hypophosphatasia (?low ALP). Clinical manifestations may be defective skeletal mineralisation resulting in osteomalacia in adults and dental problems.
Referred Test: Referred test
Location: Rotherham Hospital