- 20–40 ng/mL or 60–100 nmol/L
- 30–50 ng/mL or 75–125 nmol/L
- Deficient: Less than 30 nmol/L (12 ng/mL)
- Potential deficiency: Between 30 nmol/L (12 ng/mL) and 50 nmol/L (20 ng/mL)
- Normal levels: Between 50 nmol/L (20 ng/mL) and 125 nmol/L (50 ng/mL)
- High levels: Higher than 125 nmol/L (50 ng/mL)