Normal Free Testosterone Ranges in Women
The normal range for free testosterone in women is approximately 1.2-6.4 pg/mL (4.16-22.2 pmol/L), with variations based on age and measurement method. 1
Reference Ranges for Free Testosterone in Women
Free testosterone is considered a better index of gonadal status than total testosterone as it represents the biologically active fraction of testosterone. When evaluating testosterone levels in women, it's important to understand the following reference ranges:
- Free testosterone: 1.2-6.4 pg/mL (4.16-22.2 pmol/L) 1
- Calculated free testosterone: 1.3-5.6 pg/mL (4.5-19.4 pmol/L) 1
- Free androgen index (FAI): 0.4-2.9 (when testosterone is measured by LC-MS/MS) 2
Measurement Considerations
Several factors affect the accuracy and interpretation of free testosterone measurements:
- Measurement timing: Morning samples (between 8-10 AM) are preferred due to diurnal variation 3
- Menstrual cycle phase: While there are slight variations across the menstrual cycle, these are relatively small compared to overall variability, so reference ranges can be applied regardless of cycle day 1
- Age: Free testosterone exhibits an age-related decline in women 1
- Measurement method:
Clinical Implications
Understanding normal free testosterone ranges is crucial for diagnosing:
Androgen excess disorders:
- In PCOS, free testosterone and FAI are stronger predictors than total testosterone 2
- Values above reference ranges may indicate hyperandrogenism
Androgen deficiency:
- Low free testosterone may contribute to decreased libido, fatigue, and reduced bone density 5
Common Pitfalls to Avoid
- Relying solely on total testosterone: SHBG variations can significantly affect total testosterone without changing free testosterone levels 6
- Using inappropriate assays: Analog immunoassays may be less reliable than equilibrium dialysis or calculated free testosterone 4
- Not considering SHBG levels: Conditions that alter SHBG (pregnancy, oral contraceptives, liver disease) can affect total testosterone without changing free testosterone 6
- Single measurements: Testosterone levels should be confirmed with repeat testing due to assay variability 3
For accurate assessment of androgen status in women, free testosterone measurement by equilibrium dialysis or calculation using validated formulas provides the most clinically useful information, with reference ranges of approximately 1.2-6.4 pg/mL representing normal values for premenopausal women.