Unit Converter
Riboflavin (Vitamin B2)
(Water-Soluble Vitamin Essential for Energy Metabolism, Mitochondrial Function, Antioxidant Pathways & Red Cell Integrity)
Synonyms
- Riboflavin
- Vitamin B₂
- Lactoflavin
- Vitamin G (historical)
- FMN precursor
- FAD precursor
Units of Measurement
- nmol/L
- µg/L
- µg/dL
- µg/100 mL
- µg%
- ng/mL
Unit Conversions
Molecular Weight of Riboflavin = 376.36 g/mol
nmol/L ↔ µg/L
1 nmol/L=0.376 µg/L1\ \text{nmol/L} = 0.376\ \text{µg/L}1 nmol/L=0.376 µg/L 1 µg/L=2.66 nmol/L1\ \text{µg/L} = 2.66\ \text{nmol/L}1 µg/L=2.66 nmol/L
µg/dL to µg/L
1 µg/dL=10 µg/L1\ \text{µg/dL} = 10\ \text{µg/L}1 µg/dL=10 µg/L
ng/mL to µg/L
1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L
µg% = µg/dL
Older clinical unit.
Description
Riboflavin (Vitamin B₂) is a water-soluble vitamin required for formation of the biologically active coenzymes:
- FMN (Flavin mononucleotide)
- FAD (Flavin adenine dinucleotide)
These coenzymes are crucial for:
- Energy metabolism (electron transport chain)
- Red-ox reactions
- Lipid, carbohydrate & protein metabolism
- Detoxification pathways
- Glutathione recycling (antioxidant defense)
- Red blood cell health
Riboflavin must be obtained from diet or supplementation.
Physiological Role
1. Energy Metabolism
FMN and FAD are essential cofactors in:
- Krebs cycle
- Beta oxidation of fatty acids
- Electron transport chain (complex I & II)
2. Antioxidant Function
Supports regeneration of glutathione.
3. Hematologic Support
Maintains RBC membrane integrity:
- Deficiency → normocytic anemia + elevated RBC fragility.
4. Growth & Tissue Repair
Supports cellular growth and repair mechanisms.
5. Vitamin Conversion
Required for:
- Activation of Vitamin B₆ (PLP → active form)
- Conversion of tryptophan → niacin
Clinical Significance
LOW RIBOFLAVIN (Ariboflavinosis)
Usually due to poor dietary intake or malabsorption.
Causes
- Malnutrition
- Chronic alcoholism
- Malabsorption (celiac disease, IBD)
- Hypothyroidism
- Chronic liver disease
- Pregnancy/lactation (increased requirement)
- Long-term phenobarbital therapy (↑ metabolism)
- Dialysis (water-soluble vitamin loss)
Symptoms
- Angular cheilitis
- Cracked lips
- Glossitis (magenta tongue)
- Seborrheic dermatitis
- Photophobia
- Corneal vascularization
- Normocytic or macrocytic anemia
- Fatigue
Biochemical Clues
- ↓ RBC glutathione reductase activity
- ↓ erythrocyte FAD levels
HIGH RIBOFLAVIN
Very rare because riboflavin is water-soluble; excess is excreted.
Seen in
- High-dose supplementation
- Bright yellow urine (flavinuria) - harmless
Reference Intervals
(Tietz 8E + NIH + WHO + Mayo + ARUP)
Serum Riboflavin
- 5 – 50 µg/L
(= 13 – 133 nmol/L)
Deficiency Cutoff
- < 5 µg/L
(= < 13 nmol/L) → biochemical deficiency
Optimal Functional Status
More reliable than serum:
- Erythrocyte glutathione reductase activation coefficient (EGRAC)
- Normal: ≤1.3
- Deficiency: >1.7
- Normal: ≤1.3
Diagnostic Uses
1. Evaluation of Nutritional Deficiency
In:
- Malnutrition
- Elderly
- Chronic alcohol use
2. Malabsorption Syndromes
Celiac disease, IBD, chronic pancreatitis.
3. Anemia Workup
Especially combined B-vitamin deficiencies.
4. Monitoring Supplementation
In pregnancy or therapeutic megadose regimens.
5. Metabolic Disorders
Rare mitochondrial enzyme defects affecting flavoproteins.
Analytical Notes
- Sample: fasting plasma/serum
- Protect specimen from light (riboflavin is light-labile)
- HPLC or LC–MS/MS used for accurate quantification
- Riboflavin is unstable → process promptly
- Hemolysis may falsely elevate riboflavin due to RBC flavins
Clinical Pearls
- Riboflavin deficiency rarely occurs alone; typically coexists with other B-vitamin deficiencies.
- Symptoms often involve skin, eyes, mouth, and RBCs.
- Serum riboflavin reflects recent intake, but EGRAC reflects long-term status.
- Riboflavin supplementation safely improves migraine frequency in many adults (common clinical use).
- Bright yellow urine after dosing is normal and benign.
Interesting Fact
Riboflavin fluoresces under UV light — giving vitamin-enriched urine its characteristic bright yellow-green glow.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Water-Soluble Vitamins
- WHO Micronutrient Deficiency Guidelines
- NIH ODS - Vitamin B2 (Riboflavin) Fact Sheet
- Mayo Clinic Laboratories - Vitamin B2
- ARUP Consult - Vitamin Testing
- CDC Global Micronutrient Guidelines