What’s the Difference Between Free and Total Testosterone?

Total testosterone is all the testosterone in your blood, bound and unbound; free testosterone is the small unbound share your tissues can use directly. Most of your testosterone rides on two proteins: a large share is bound tightly to sex hormone-binding globulin (SHBG), a smaller share is bound loosely to albumin, and only a small proportion is free (Mayo Clinic Laboratories). A total testosterone test counts all three together, so it can't tell you how much is free (MedlinePlus).

For most men the total is the right first test. The free number matters most when the total sits near the low end of normal or when something has pushed SHBG up or down.

How is testosterone carried in the blood?

• SHBG-bound testosterone. SHBG is a protein made mostly in the liver. Testosterone attached to it can't act on your tissues (MedlinePlus).
• Albumin-bound testosterone. Albumin holds testosterone weakly, and it lets go in the small blood vessels, so this share is readily available to tissues (Mayo Clinic Laboratories).
• Free testosterone. Unbound and active. In men it helps control sex drive, muscle and bone growth, sperm production, and red blood cell production (MedlinePlus).

Free plus albumin-bound testosterone is called bioavailable testosterone. A bioavailable test measures everything not bound to SHBG (MedlinePlus).

Why can free testosterone be low when total testosterone is normal?

Because SHBG decides how the total is split. When SHBG is high, more of the total is locked up and less is free. When SHBG is low, more is free, even if the total looks low.

Things that tend to raise SHBG, and so lower the free share:

• Getting older. In the European Male Ageing Study (EMAS), SHBG rose with age while total testosterone fell, so calculated free testosterone fell further than the total (Antonio et al., JCEM 2016).
• Liver disease, an overactive thyroid (hyperthyroidism), and some eating disorders (MedlinePlus).
• Some medicines, including corticosteroids and sex steroids such as oral estrogen (Mayo Clinic Laboratories).

Things that tend to lower SHBG: obesity, type 2 diabetes or insulin resistance, an underactive thyroid (hypothyroidism), anabolic steroid use, and Cushing's syndrome (MedlinePlus). For a longer look at the high side, see what causes high SHBG.

Does low free testosterone cause symptoms when the total is normal?

It is associated with them. EMAS measured 3,334 men aged 40 to 79 living in the community (Antonio et al., JCEM 2016). The 277 men with a normal total (at or above 10.5 nmol/L, about 300 ng/dL) but low calculated free testosterone were older and in poorer health, had higher SHBG, and reported more sexual and physical symptoms than men with both numbers normal. They also had lower hemoglobin and weaker bone ultrasound results.

The study also looked at the opposite pattern. Men with a low total but normal free testosterone were younger and more obese, had low SHBG, and lacked features of testosterone deficiency.

This was an observational study. It shows an association at one point in time, and it can't show that low free testosterone caused the symptoms or that treating it would relieve them. The men with low free testosterone were also in poorer health overall.

When is free testosterone tested?

Both major guidelines start with total testosterone.

• The Endocrine Society recommends a fasting morning total testosterone as the first test, repeated to confirm. It recommends a free testosterone result "in men whose total T is near the lower limit of normal or who have a condition that alters sex hormone-binding globulin" (Endocrine Society 2018).
• The AUA uses a total testosterone below 300 ng/dL, measured on two separate early-morning occasions, as the cut-off that supports a diagnosis (Moderate Recommendation, Grade B) (AUA 2018).

Morning matters because levels are typically highest between about 7 and 10 a.m. (MedlinePlus); more on that in when testosterone peaks in the morning. Levels can also swing substantially from day to day, so one result is not enough to judge your testosterone status (Mayo Clinic Laboratories).

Where the cut-off sits also varies. A study that recalibrated four large cohorts to a reference method put the normal range for healthy, nonobese men aged 19 to 39 at 264 to 916 ng/dL, and found that much of the variation between cohorts came from assay differences (Travison et al., JCEM 2017).

How is free testosterone measured, and which method is accurate?

Labs use three approaches, with different accuracy.

• Equilibrium dialysis. This measures free testosterone directly. It is technically demanding and costly, so it is not commonly available, and most clinicians rely on a calculated value instead (2024 review).
• Calculated free testosterone. A formula estimates free testosterone from total testosterone and SHBG. In one comparison, calculated values were almost identical to dialysis values in every condition tested except pregnancy (Vermeulen et al., JCEM 1999). Calculators are not standardized, though, and give approximations (2024 review).
• Direct "analog" immunoassays. These gave values that were only a fraction of the dialysis result, and the gap varied with SHBG. The same study found them unreliable (Vermeulen et al., JCEM 1999).

Free testosterone reference ranges depend on the lab and the method, so compare your result with the range printed on your own report, not with a number from the internet.

What symptoms point to low testosterone?

In adult men, symptoms that lead to a testosterone test include low sex drive, erectile dysfunction, infertility, enlarged breasts, loss of face or body hair, thinning bones or anemia without a known cause, and loss of muscle mass (MedlinePlus).

Symptoms start the evaluation; they don't settle it. Both guidelines diagnose low testosterone only when symptoms or signs come with consistently low lab results (AUA 2018; Endocrine Society 2018). Fatigue, low mood, and poor sleep have many other causes, so a man with symptoms and normal repeat results needs a search for those causes.

What else might be checked if testosterone is low?

Once low testosterone is confirmed, the next step is finding the cause (Endocrine Society 2018). The AUA recommends measuring luteinizing hormone (LH, the pituitary signal that tells the testes to make testosterone) in men with low testosterone (AUA 2018).

Estradiol is not a routine part of this workup. The AUA ties it to men who have breast symptoms or gynecomastia (breast tissue growth) before starting testosterone therapy (statement 9, Expert Opinion) (AUA 2018).

Common questions

My total is normal but my free testosterone is low. Does that mean I need TRT?

Not by itself. The Endocrine Society uses free testosterone to help decide borderline cases, alongside symptoms and repeat morning tests (Endocrine Society 2018). A clinician will also look at why SHBG is high, since causes such as thyroid or liver disease need their own care.

Can I raise my free testosterone without medication?

In men with obesity, weight loss helps. A meta-analysis of 24 studies found that weight loss from diet or bariatric surgery raised both bound and unbound testosterone, with larger rises in men who lost more weight (Corona et al., Eur J Endocrinol 2013).

Is a low total always low testosterone?

Not always. In EMAS, men with a low total but normal free testosterone were on average younger and more obese, with low SHBG, and they lacked features of deficiency (Antonio et al., JCEM 2016). That is one reason a low total is repeated and read alongside SHBG and symptoms.

Bottom line

Total testosterone counts everything in your blood; free testosterone is the small share your tissues can use right away, and SHBG decides the split. Total testosterone is the first test, and free testosterone, ideally by equilibrium dialysis or a calculation from total testosterone and SHBG, helps when the total is borderline or SHBG is abnormal. Low free testosterone with a normal total is linked to symptoms in observational data, but the diagnosis still rests on symptoms plus consistently low morning results. If your results point that way, AlphaMD providers review your labs before discussing testosterone replacement therapy.