The main circulating forms of vitamin B₆ are pyridoxal phosphate (PLP), pyridoxal (PL), and pyridoxic acid (PA). The active form in the body is PLP. It acts as a coenzyme for many enzymes in the body and is involved in metabolism of proteins, carbohydrates, and fats, production of serotonin and haem, and binding of steroid hormones to their receptors.

Deficiency is associated with various symptoms: irritability, depression, and confusion, inflammation of the tongue and sores or ulcers of the mouth.

PLP is a cofactor in homocysteine metabolism and aids in the metabolism of homocysteine to cysteine so lowering its impact on cardiovascular disease. Vitamin B₆ has been widely used as a treatment of premenstrual tension although the evidence supporting its use is weak. Chronically high concentrations of vitamin B₆ can be toxic resulting in peripheral neuropathy.

Vitamin B₆ is almost entirely bound to albumin and so plasma levels fall during the acute phase response. In contrast, we have shown that red cell vitamin B₆ concentrations are unaffected and for this reason have switched from plasma to red cell concentration for assessing vitamin B₆ status.

Sample Requirements and Reference Ranges for Vitamin B₆

* This is the absolute minimum volume; these volumes are insufficient to carry out a repeat analysis in the event of an analytical problem.

** Please contact the Laboratory if vitamin B₆ in plasma is required.