ABSTRACT
Biochemical status tests are usually required to substantiate riboflavin deficiency. Subclinical deficiency is assessed by measurement of erythrocyte glutathione reductase (EGR), which requires FAD as the cofactor. The enzyme catalyzes the conversion of glutathione to reduced glutathione with the participation of NADPH. The assay follows the in vitro stimulation of EGR activity through the addition of FAD. The spectrophotometric assay results are converted to an activity coefficient, which rises in subjects to a riboflavin intake level of 0.5 mg 1000 kcal−1.3
Riboflavin levels in urine based on 24 h urine collections can be used to confirm EGR observations. As for thiamin, riboflavin concentrations in blood, serum, and erythrocytes are not dependable measures of status owing to subject variability.
