An analytical measurement of the Riboflavin (Vitamin B2) concentration actively circulating within the blood serum. This crucial vitamin serves as a fundamental biochemical cofactor indispensable to numerous cellular oxidation-reduction (redox) reactions. A sustained, adequate level of Riboflavin is essentially required for optimized cellular energy production, mitochondrial health, and the sustained biological maintenance and regeneration of both the integumentary system (the skin) and the mucosal membranes.