Free vs Total Testosterone: What the Difference Means for Your Health

Here is one of the most common scenarios I encounter: a man comes to me with classic low testosterone symptoms — fatigue, reduced libido, brain fog, difficulty building muscle. His doctor ran a total testosterone test, saw 520 ng/dL, and told him everything is fine. He’s suffering, but his labs say he’s normal.

When I run his full panel, I find free testosterone at 7.2 pg/mL (well below the performance threshold of 15+), SHBG elevated at 68 nmol/L, and estradiol high-normal. Total T is in range. Free T is not. The doctor only looked at half the picture.

Understanding Testosterone Fractions

Testosterone in your blood exists in three forms:

• Bound to SHBG: Approximately 44–65% of your total testosterone is tightly bound to SHBG and completely unavailable to your cells. This testosterone is biologically inactive.
• Bound to albumin: Another 33–54% is loosely bound to albumin. This portion is considered “bioavailable” — it can be released and used by tissues.
• Free testosterone: Only 1–3% of your total testosterone circulates completely unbound. This is the immediately bioavailable form that binds directly to androgen receptors in your muscle, brain, bone, and other tissues.

When your doctor orders “testosterone,” they typically get total testosterone — which includes all three fractions. A high SHBG level can make total testosterone look fine while starving your cells of the free fraction they actually need.

What Is a Healthy Free Testosterone Level?

What Is SHBG and Why Does It Matter?

SHBG is a glycoprotein produced primarily by the liver. Its job is to bind sex hormones (testosterone and estrogen) and regulate how much is available to tissues at any given time. When SHBG is elevated, it captures more testosterone and leaves less free — even if total production is adequate.

SHBG rises with age, thyroid disease, liver disease, low insulin (very low-carb diets), and certain medications. High SHBG is one of the most underdiagnosed causes of functional testosterone deficiency in men over 40.

Causes of Elevated SHBG

• Aging (SHBG naturally increases ~1–2% per year after 40)
• Hyperthyroidism
• Liver disease (cirrhosis, hepatitis)
• Very low-carbohydrate or ketogenic diets
• Alcohol consumption
• Certain medications (anticonvulsants, some antidepressants)

How to Lower SHBG Naturally

• Optimize insulin sensitivity: Resistance training and strategic carbohydrate inclusion help lower SHBG through insulin’s suppressive effect.
• Maintain healthy body weight: Obesity is associated with altered SHBG dynamics.
• Optimize thyroid function: Subclinical hypothyroidism is a common driver of SHBG changes.
• Limit alcohol: Even moderate consumption raises SHBG and suppresses testosterone production directly.
• Consider boron supplementation: Research suggests 6–10mg of boron daily may reduce SHBG. Discuss with your physician.