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Biotin (Vitamin B7)
(Water-soluble B-complex vitamin – Coenzyme for Carboxylases)
Synonyms
- Biotin
- Vitamin B7
- Vitamin H
- Coenzyme R
- D-Biotin
Units of Measurement
- nmol/L
- ng/L
- ng/dL
- ng/100 mL
- ng%
- pg/mL
Description
Biotin is a water-soluble B-complex vitamin required as a coenzyme for five major carboxylases, which are essential in:
- Fatty acid synthesis
- Gluconeogenesis
- Branched-chain amino acid metabolism
- Energy production
Biotin levels are measured to evaluate:
- Biotin deficiency
- Biotinidase deficiency in infants
- Malabsorption syndromes
- Long-term parenteral nutrition
- Unexplained dermatitis/alopecia/metabolic acidosis
⚠️ Biotin supplementation can interfere with immunoassays, causing falsely high or low lab results. (Important for thyroid, hormone, troponin tests.)
Physiological Role
Biotin acts as a coenzyme for:
- Pyruvate carboxylase – gluconeogenesis
- Acetyl-CoA carboxylase – fatty acid synthesis
- Propionyl-CoA carboxylase – amino acid metabolism
- Methylcrotonyl-CoA carboxylase – leucine metabolism
- β-methylcrotonyl-CoA carboxylase
Biotin is also crucial for:
- Gene regulation
- Keratin infrastructure (skin/hair health)
- Immune function
Clinical Significance
Low Biotin (Deficiency)
Causes:
1. Biotinidase Deficiency (Most important in infants)
- Autosomal recessive
- Severe deficiency → seizures, metabolic acidosis, developmental delay
- Newborn screening required
2. Malnutrition / Poor Intake
Seen in:
- Severe malnutrition
- Chronic alcoholism
- Pregnancy (increased requirement)
3. Long-term Raw Egg Consumption
Avidin in raw egg whites binds biotin → deficiency.
4. Malabsorption Syndromes
- Crohn disease
- Short bowel
- Chronic diarrhea
5. Long-term Antibiotics
Destroys gut bacteria that synthesize biotin.
Clinical Features of Deficiency
- Alopecia
- Dermatitis (periorificial, seborrheic)
- Conjunctivitis
- Depression, lethargy
- Ataxia
- Metabolic acidosis (in severe enzyme defects)
High Biotin
Usually from supplementation:
- Hair/skin/nail formulas
- High-dose biotin therapy for multiple sclerosis (100–300 mg/day)
⚠️ High-dose biotin causes significant interference in many hormone and immunoassays, leading to:
- Falsely low TSH
- Falsely high T3/T4
- Falsely low troponin → dangerous in myocardial infarction
Patients should stop biotin 24–72 hours before lab testing.
Reference Intervals
(Tietz 8E + NIH + Mayo + ARUP)
Values vary based on diet and supplements.
Serum Biotin (Adults)
- 200 – 1200 ng/L
- 0.2 – 1.2 ng/mL
- ≈ 0.8 – 4.9 nmol/L
Biotinidase Deficiency Screening
- Enzyme activity low → not based on serum biotin level
- Serum biotin may be normal; enzyme activity test required
Infants
- Slightly higher levels due to supplementation in formulas
Unit Meanings
| Unit | Meaning |
| nmol/L | nanomole per liter |
| ng/L | nanogram per liter |
| ng/dL | nanogram per deciliter |
| ng/100 mL | same as ng/dL |
| ng% | nanogram per 100 mL (identical to ng/dL) |
| pg/mL | picogram per milliliter |
Diagnostic Uses
1. Suspected Biotin Deficiency
- Dermatitis
- Alopecia
- Lethargy
- Metabolic acidosis
- Infant metabolic disorders
2. Monitoring High-Dose Biotin Therapy
Used in:
- Multiple sclerosis (experimental therapy)
3. Nutritional Evaluation
Especially in:
- Malnourished
- GI surgery patients
- Long-term TPN
4. Inborn Errors of Metabolism
- Biotinidase deficiency
- Holocarboxylase synthetase deficiency
5. Laboratory Interference Check
Suspected when:
- Thyroid tests discordant
- Troponin unexpectedly low
- PTH/hormone tests inconsistent with symptoms
Analytical Notes
- Serum or plasma (heparin/EDTA acceptable).
- Avoid biotin supplements at least 48 hours before testing.
- Assay: LC–MS/MS (gold standard) or immunoassay.
- Light-stable; hemolysis minor effect.
Clinical Pearls
- Biotin deficiency presents with skin + neuro + metabolic symptoms.
- Routine multivitamins rarely cause abnormal results; high-dose supplements do.
- Serum biotin is not the diagnostic test for biotinidase deficiency - enzyme activity is required.
- Hair/skin supplements often contain 5,000–10,000 µg biotin → enough to confuse lab assays.
Interesting Fact
Biotin was historically called "Vitamin H"-from the German words Haar (hair) and Haut (skin)-because deficiency causes hair loss and dermatitis.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Vitamins.
- NIH - Office of Dietary Supplements (Biotin Fact Sheet).
- IFCC - Vitamin Assay Standardization.
- Mayo Clinic Laboratories - Biotin.
- ARUP Consult - Vitamin Disorders.
- AACC Guidelines - Biotin Interference in Immunoassays.