Vitamin B6 (pyridoxine) is a water-soluble vitamin that serves as a coenzyme in over 100 enzymatic reactions, particularly in amino acid metabolism, neurotransmitter synthesis, and energy production. This test measures the active form of vitamin B6, pyridoxal 5'-phosphate (PLP), in the blood to evaluate nutritional status and diagnose deficiency. Vitamin B6 deficiency can cause various symptoms including anemia, neurological problems, skin disorders, and impaired immune function. Low levels are common in individuals with poor dietary intake, malabsorption disorders, alcoholism, or those taking certain medications like isoniazid or oral contraceptives. Vitamin B6 is particularly important for brain health, red blood cell formation, and protein metabolism. This test is commonly ordered when evaluating unexplained neurological symptoms, anemia, or when monitoring nutritional status in high-risk populations. Early detection and treatment of vitamin B6 deficiency can prevent serious complications and improve overall health outcomes.