Hormones
Testosterone / SHBG Ratio (Free Androgen Index)
What This Marker Tells Us
Estimates bioavailable testosterone by comparing total testosterone to SHBG, which binds and inactivates testosterone, revealing how much testosterone is actually free to act on tissues.
Why It Matters
SHBG binds roughly 60% of testosterone, rendering it inactive. High SHBG lowers free testosterone despite normal total testosterone, causing symptoms. Low SHBG increases free testosterone, potentially causing androgenic effects even with normal total testosterone. The ratio reveals true androgenic activity affecting muscle growth, libido, energy, cognition, and metabolic health.
How to Interpret Your Trends
Low ratios indicate reduced bioavailable testosterone from high SHBG or low total testosterone, causing symptoms like reduced libido, energy, muscle mass, and cognitive function. Typical ratios suggest adequate bioavailable testosterone for physiological functions. High ratios indicate elevated free testosterone from low SHBG or high total testosterone, potentially beneficial for muscle and performance but concerning for prostate health or causing androgenic effects in women.
What Influences This Marker
Insulin resistance and obesity lower SHBG, raising free testosterone. Aging, estrogen, thyroid hormones, and certain medications raise SHBG, lowering free testosterone. Liver disease affects SHBG production. Exercise, weight loss, and metabolic optimization normalize SHBG. Low-carb diets may lower SHBG. Genetics significantly influence baseline SHBG levels.
How Your Team Uses It
Your coach uses this ratio to assess true androgenic activity beyond total testosterone, guiding whether symptoms reflect testosterone deficiency or SHBG abnormalities. Low ratios despite adequate total testosterone prompt metabolic optimization and SHBG management rather than testosterone therapy. High ratios guide monitoring for androgenic excess effects.
Related Signals We Also Review
Total testosterone, SHBG, free testosterone (if measured directly), estradiol, DHEA-S, insulin resistance markers, and liver function complete the androgen status assessment.