Vitamin B5 (pantothenic acid) is a water-soluble vitamin that plays a crucial role in energy metabolism and the synthesis of essential compounds. This test measures vitamin B5 levels in the blood to evaluate nutritional status and diagnose deficiency. Vitamin B5 is a component of coenzyme A (CoA), which is essential for the Krebs cycle, fatty acid synthesis, and the production of cholesterol, steroid hormones, and neurotransmitters like acetylcholine. Deficiency can cause symptoms including irritability, fatigue, sleep disturbances, nausea, vomiting, abdominal cramps, numbness, muscle cramps, and hypoglycemia. While severe deficiency is rare in developed countries, it can occur in individuals on semisynthetic diets or those with malabsorption syndromes. This test is particularly valuable for evaluating patients with unexplained neurological symptoms, monitoring nutritional therapy, and assessing metabolic disorders.