Vitamin B6
Overview
Vitamin B6 measures serum levels of pyridoxal 5'-phosphate (PLP), the active coenzyme form essential for amino acid metabolism, neurotransmitter synthesis, and heme production. It functions as a cofactor for over 100 enzymatic reactions including glycogenolysis, gluconeogenesis, and homocysteine metabolism. Low levels indicate poor dietary intake, malabsorption, alcoholism, or drug-induced deficiency causing peripheral neuropathy or sideroblastic anemia, while high levels from megadosing cause sensory neuropathy; clinically useful for diagnosing deficiency in at-risk patients and monitoring supplementation in renal disease or isoniazid therapy.
Clinical Use Cases
- Diagnosing vitamin B6 deficiency neuropathy.
- Monitoring isoniazid or cycloserine therapy toxicity.
- Evaluating sideroblastic anemia etiology.
- Assessing homocystinuria or hyperhomocysteinemia.
- Screening chronic alcoholics or bariatric surgery patients.
Specimen Types
- Serum (preferred).
- Plasma (EDTA).
- Whole blood (pyridoxal phosphate).
Measurement Methods
- High-performance liquid chromatography (HPLC) with fluorescence detection.
- Enzymatic assays.
- Liquid chromatography-tandem mass spectrometry (LC-MS/MS).
Test Preparation and Influencing Factors
- Fasting preferred (4-8 hours).
- Avoid vitamin B6 supplements 24-48 hours prior.
- Isoniazid, penicillamine, oral contraceptives deplete levels.
- Renal failure, alcoholism, malabsorption lower levels.
- Megadosing causes reversible toxicity.
Synonyms
- Pyridoxal 5'-phosphate (PLP).
- Pyridoxine.