Vitamin B2 (riboflavin) is a water-soluble vitamin essential for energy production and cellular metabolism. This test measures vitamin B2 levels in whole blood to evaluate nutritional status and diagnose deficiency. Vitamin B2 serves as a precursor for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are critical for numerous metabolic reactions including oxidative phosphorylation, fatty acid oxidation, and amino acid metabolism. Deficiency can cause characteristic symptoms including angular stomatitis (cracks at the corners of the mouth), glossitis (inflammation of the tongue), corneal vascularization, and seborrheic dermatitis. Vitamin B2 deficiency is common in developing countries and can also occur in industrialized nations, particularly in the elderly and those with poor dietary intake. This test is particularly valuable for evaluating unexplained skin and mucosal lesions, monitoring nutritional therapy, and assessing vitamin B2 status in high-risk populations.