What is S-Testosterone/SHBG Ratio?
Last updated: 30 June 2026
Reviewed by: Elfcare quality team
The S-Testosterone/SHBG ratio, also known as the Free Androgen Index (FAI), compares your total testosterone to the amount of SHBG (Sex Hormone-Binding Globulin) in your blood. This ratio gives a clearer picture of bioavailable testosterone, the portion of the hormone that is actually free to enter your cells and have an effect.
The role of the ratio in the body
SHBG binds tightly to testosterone, keeping it inactive while it's bound. The ratio tells us how much testosterone is unbound or loosely bound, and therefore available for the body to use. This matters because total testosterone can look normal while SHBG is also very high, in which case the body may still experience symptoms of a hormone deficiency despite the total number appearing fine.
Why test the testosterone/SHBG ratio?
Standard total testosterone tests often miss the full picture, particularly for people with metabolic issues, those on certain medications, or those further along in the aging process. Testing this ratio reveals the active portion of your testosterone, helping to explain symptoms like low energy, stalled muscle growth, or low libido even when total testosterone looks normal.
You should be extra attentive to this marker if you:
Are a man with normal total testosterone but symptoms consistent with Low T.
Are a woman investigating symptoms of PCOS, such as unwanted hair growth or persistent acne.
Are managing weight or metabolic health, as insulin levels heavily influence SHBG.
Want a clearer view of your body's capacity for muscle repair and growth.
High ratio: what does it mean?
A high ratio means that a large percentage of your testosterone is free and active.
Elevated ratios may indicate:
High free androgens: In women, a high ratio is one of the most sensitive indicators of PCOS or adrenal overactivity.
Low SHBG: This is often linked to high insulin levels, obesity, or a diet high in refined sugars.
Enhanced anabolic state: In men, a high-normal ratio generally suggests excellent hormone availability for muscle repair and energy.
Low ratio: what does it mean?
A low ratio suggests that even with adequate total testosterone, too much of it is bound to SHBG. This leaves very little SHBG available for your tissues to use.
Common reasons for low levels include:
High SHBG: Often caused by aging, high estrogen levels, an overactive thyroid, or certain liver conditions that increase its production. Prolonged calorie restriction or crash dieting can also push SHBG higher.
Hormonal insufficiency: In men, this is often behind symptoms of fatigue and low libido, even when total testosterone looks acceptable.
Overtraining: Excessive physical stress can lower total production while maintaining or raising SHBG, causing the ratio to crash.
Practical steps for ratio optimization
You can support a healthy ratio by managing both testosterone production and SHBG levels together.
Manage insulin levels: High insulin lowers SHBG too much. Reducing refined carbs and liquid sugars helps bring SHBG back to a healthy range, balancing the ratio.
Prioritize protein and zinc: Avoiding extreme calorie or protein restriction helps keep SHBG from rising unnecessarily, while adequate zinc intake supports the body's production of testosterone.
Limiting alcohol: Chronic alcohol consumption can raise SHBG and lower testosterone at the same time, which can significantly affect the ratio.
Strength training: Lifting heavy weights helps increase total testosterone production while improving insulin sensitivity, which optimizes the ratio.
Disclaimer: These results should always be discussed with a healthcare professional. This guide is for informational purposes and is not medical advice.
Testing with Elfcare
The S-testosterone/SHBG ratio is included in Elfcare’s blood test package and in our full body health check. We analyse this ratio alongside albumin to calculate your free testosterone value, giving you the most accurate possible assessment of your bioavailable hormone levels.
Understanding your Testosterone/SHBG ratio is a key step in proactive health. Elfcare’s tests provide the data you need to act before imbalances affect your daily life.
Summary
The S-Testosterone/SHBG ratio represents the active, usable portion of your testosterone.
A high ratio in women often signals PCOS, while a low ratio in men often explains symptoms of fatigue despite normal total testosterone.
Lifestyle factors like insulin management and strength training are among the most effective ways to maintain a healthy balance.
Mastering your hormone ratio allows you to ensure your body isn't just producing hormones, but actually using them to support your strength, mood, and overall vitality.
Last updated: 30 June 2026
Reviewed by: Elfcare quality team
