Biotin is a vitamin sold in large doses as a supplement for hair, skin, and nails. It switches on a small set of enzymes that build and break down fat, make new sugar, and clear certain amino acids. Replacing it clearly helps only people who cannot obtain or recycle it. Beyond that, blood-fat findings are firmest, hair and nail evidence weakest, and concentrated doses can distort most automated blood tests. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Urinary 3-hydroxyisovaleric acid | <195 mmol per mol creatinine | Earliest functional sign of biotin depletion |
| Serum 3-hydroxyisovaleryl carnitine | No established target; track against the reporting laboratory's reference interval and the pre-supplement value | Practical single-draw alternative to the urinary marker |
| Serum biotin | 0.2–1.2 µg/L unsupplemented; ≥10 µg/L is the interference threshold | Confirms whether a distorted result is biotin-driven |
| Thyroid-stimulating hormone with free thyroxine | Thyroid-stimulating hormone 0.5–2.0 mIU/L | Detects both genuine thyroid disease and the classic falsely-low pattern |
| High-sensitivity cardiac troponin T | <14 ng/L | The assay where a falsely low result is most dangerous |
| Fasting triglycerides | <100 mg/dL (1.13 mmol/L) | Tracks the best-supported metabolic benefit |
| Glycated hemoglobin | <5.4% | Tracks glycemic response without biotin interference |
Cadence: Baseline while biotin-free, repeat at 12 weeks, then every 6–12 months, always after a 72-hour washout