Vitamin B2 is a water soluble vitamin.The main circulating forms of vitamin B2 are riboflavin and its two cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These two forms are detectable in both plasma and blood cells, however, the predominant form is FAD found in red blood cells. FMN and FAD act as cofactors in oxidation-reduction reactions and in the respiratory chain and are thus involved in energy production (eg. cytochrome, glutathione reductase, glutathione peroxidase, xanthine oxidase and methylene tetrahydrofolatereductase). Flavins also have antioxidant functions, removing free radicals to reduce oxidative damage to lipids and other macromolecules. As an antioxidant, FAD is a coenzyme to glutathione reductase. Flavin coenzymes are also involved in the metabolism of four other vitamins – vitamin B12, folic acid, vitamin B6 (for conversion to the coenzyme pyridoxal 5 phosphate) and niacin (conversion of tryptophan to niacin).
Deficiency and Toxicity
Body stores of vitamin B2 are low, so deficiency can develop fairly quickly when intake is inadequate or losses are excessive.
Specific vitamin B2 deficiency is very rare; it usually occurs in combination with other water soluble vitamin deficiencies as a result of malabsorption states (such as coeliac disease and Crohn’s disease), increased losses (e.g. during renal dialysis) and in the elderly and in alcoholics as a result of inadequate nutrition, and impaired digestion and absorption. Functional deficiency may also be induced by diseases such as hypothyroidism and adrenal insufficiency and by drugs such as chlorpromazine, imipramine and amitryptamine.
Symptoms of deficiency are sore throat, inflammation of mouth, tongue and throat, cracks in lips and corners of mouth, normocytic normochromic anaemia, and dermatitis.
Catabolic patients and patients with systemic infections may have increased requirements due to enhanced excretion, increased utilization, decreased intake, defective absorption and poor utilization.
Vitamin B2 is essentially non-toxic.
Assessment of status
Plasma vitamin B2 (FAD) is extensively bound to albumin and so concentrations fall in the presence of systemic inflammatory response independent of vitamin B2 nutritional status. This is because plasma albumin concentrations fall as part of the systemic inflammatory response and also perhaps due to the redistribution of FAD and increased uptake by tissues.
Work done in this unit has shown that the red cell FAD concentration is unaffected by systemic inflammatory response in patients 48 hours after undergoing elective surgery for knee arthroplasty,76 whereas the plasma FAD concentration decreases significantly (see Table). Red cell FAD also reflects supplementation in patients with critical illness.77 We therefore recommend the measurement of FAD in red cells in patients that have evidence of systemic inflammatory response. Results are expressed as nmoles of FAD per g of haemoglobin.
We routinely only report red cell FAD for assessment of vitamin B2 status. However, if required, plasma or whole blood riboflavin and FAD can be measured to assess vitamin B2 status in patients who are non-inflamed, for monitoring of patients with the genetic neurodegenerative disorder Brown-Vialetto-Van Laere syndrome, and for research studies.
Recommended Daily Allowance
Adults: 1.3 mg/day
Effect of Systemic Inflammatory Response on Plasma Vitamin B2 Concentrations
Table: Baseline, peak/ trough and day 7 concentrations of CRP, plasma and red cell flavin adenine dinucleotide (FAD) and albumin following elective surgery for knee arthroplasty (n = 20).76 Median (range).
|C-reactive protein (mg/L)||<6 (<6–<6)||170 (70–242)||31 (<6–168)||<0.001|
|Plasma FAD (nmol/L)||62 (52 – 105)||39 (24 – 76)||66 (36 – 97)||<0.001|
Red cell FAD
|2.45 (1.70 – 3.90)||2.7 (1.8-3.9)||2.70 (1.90 – 3.80)||0.115|
Sample Requirements and Reference Ranges for Vitamin B2
|Sample Type||Whole blood or packed red blood cells (please label tube as red cells; fasting sample preferred*).|
|Container||Lithium heparin (non-gel) or EDTA. Lithium heparin gel tubes unsuitable.|
Light-sensitive; wrap in tin foil. Send whole blood by first class post within 72 hours (do not freeze whole blood).
If delivery to Glasgow is outwith 72 hours of sample collection, prepare red cells (minimum volume 300 µL) by removing and discarding plasma and buffy layer (mark clearly on tube that they are red cells) and store frozen until sending and then send by first class post (ice or dry ice not required).
|Minimum volume**||1 mL whole blood or 400 µL of red cells*** (Vitamin B6 can be analysed simultaneously on this volume).|
|Reference range||Red cell FAD: 1.0 to 3.4 nmol/g Hb (In-house, n = 126)|
|Mean turnaround time||3.3 days|
|Method||HPLC with fluorimetric detection78|
|Traceability||EQA. Please contact laboratory for current EQA performance.|
|Intermediate Precision (CV)||4.4% at 1.5 nmol/g Hb, 4.2% at 5.6 nmol/g Hb|
|Measurement Uncertainty, U||2.1 ± 0.29 nmol/g Hb, 3.1 ± 0.37 nmol/g Hb|
|Analytical Goals (CV)||Acceptable 4.8%, Desirable 3.2%****|
|EQA Scheme||INSTAND (whole blood EQA scheme), Düsseldorf, Germany (four times per year).|
* Ideally a fasting sample should be collected, especially if the patient is receiving oral or parenteral vitamin B2 supplementation. If this is not possible, sample should be taken at least 8 hours post treatment for patients receiving oral supplementation or TPN.
** Absolute minimum volume; this volume is insufficient to carry out repeat analysis if analysis fails.
*** Please contact the Laboratory if vitamin B2 in whole blood or plasma is required.
**** Calculated from biological variation data.71