Total vs. free testosterone: What’s the difference & why it matters

Testosterone is the quintessential male hormone (androgen), and it’s a busy one, helping to regulate intimate function, muscle mass, red blood cell count, mood, and more.

But not all testosterone in your bloodstream is ready for action. Most of it is bound to proteins, making it unavailable. Only a small fraction circulates freely — known as free testosterone — and this is the portion that’s biologically active to exert those vital effects in your body.

Total testosterone refers to both bound and unbound (or free) testosterone in your blood.

Below, we’ll explain more about the difference between total testosterone and free testosterone, what most blood tests actually measure, and what you can do to keep your levels in a healthy range.

The pituitary gland in your brain controls how much testosterone your body makes by signaling other hormones, like luteinizing hormone (LH). LH then stimulates the Leydig cells in the testes to produce testosterone (though a small amount is also made by the adrenal glands).

Total testosterone refers to the total amount of testosterone circulating in your body. Most of the testosterone circulating in your blood — about 98 percent — is bound to proteins made by your liver called “intimacy” hormone-binding globulin (SHBG) and albumin. The remaining 2 to 3 percent of your testosterone is unbound and available for your body to use at any given time.

Total serum testosterone levels have been shown to gradually decline at a rate of about 1 percent per year starting at age 40.

When a doctor orders a blood test to check for low testosterone levels, they’ll typically order a total testosterone test first.

We already mentioned that total testosterone encompasses bound and unbound testosterone. But what does it mean for testosterone to be bound or unbound?

Bound Testosterone

Testosterone and other male hormones are bound to proteins like albumin and S hormone–binding globulin. These proteins hold most testosterone in reserve, while controlling how much free hormone is circulating at any given time.

The testosterone bound to SHBG is tightly bound and generally not biologically available. SHBG levels influence total testosterone readings. In general, higher levels of SHBG mean lower levels of free testosterone. That’s because SHBG binds tightly to testosterone in the blood, making it unavailable for the body to use. As SHBG rises, the amount of free testosterone left to act on tissues decreases. SHBG is often elevated in older men with low testosterone, but it can be low in men with obesity, insulin resistance, or metabolic syndrome.

Albumin-bound testosterone is weakly bound, so it can detach easily and be used by tissues when needed. Though it’s not technically considered free, testosterone bound weakly to albumin is often called bioavailable testosterone because it can readily cross into cells. For this reason, albumin-bound testosterone is included in calculations of bioavailable testosterone, even though it isn’t classified as truly “free.”

Free Testosterone

Free testosterone is the type that is unbound to proteins and metabolically active. It circulates and directly binds to receptors, where it can exert its effects.

Measuring free testosterone is key to diagnosing testosterone deficiency in men (i.e., hypogonadism or low testosterone) and high testosterone in women, which can occur alongside polycystic ovary syndrome, or PCOS, and hirsutism. However, providers typically measure total testosterone first before testing SHBG levels, which indicate your free testosterone levels.

Some research suggests that free testosterone may correlate more strongly with intimate health than total testosterone, though findings are mixed. Both measures are clinically relevant, and interpretation often depends on the individual case.

Free testosterone is also more closely tied to body composition than total testosterone. Research shows it directly correlates to lean muscle mass, strength, and physical function in older men.

A testosterone test can measure two things: your total testosterone or your free testosterone. Total testosterone measures the overall testosterone concentration, both bound and unbound, while free testosterone measures just the small amount that isn’t tied up to proteins.

Most of the time, doctors check total testosterone first when you have symptoms like low energy, low drive, mood changes, or trouble with arousals. They may also use it to track how well treatment like testosterone therapy is working.

It’s the initial screening test for diagnosing male hypogonadism, androgen excess, or other hormone-related disorders in both men and women. Total testosterone testing may also be used to evaluate delayed puberty, infertility, ED, and endocrine disorders.

A free testosterone test is usually done only if the total testosterone result doesn’t explain your symptoms, or if you have health issues (like obesity, diabetes, or thyroid problems) that can affect how testosterone is carried in your blood.

How Is a Total Testosterone Test Performed?

Total testosterone tests can be taken in a lab or at home. Providing a blood sample is the most reliable way to test your hormone levels, though some labs may test your saliva.

In adult males, testing is typically done in the morning when testosterone levels are highest. You may be asked to refrain from eating or drinking before the test.

According to the American Urological Association (AUA), low testosterone is defined as a total testosterone level under 300 ng/dL. For a diagnosis, the test should be repeated on two different mornings, and the low result must be paired with symptoms of testosterone deficiency — such as reduced drive, fatigue, or loss of muscle mass.

Because total testosterone test results can be influenced by factors such as illness, medications, and SHBG levels, testing free testosterone, or bioavailable testosterone, can sometimes provide a more accurate assessment of hormone levels.

A total testosterone blood test shouldn’t take more than five minutes, and results typically take a couple of days, depending on the laboratory.

What Do the Test Results Mean?

Normal total testosterone levels vary slightly depending on the laboratory, the testing method, and patient demographics.

A normal total testosterone range is between 300 and 1,000 ng/dL. Levels below 300 ng/dL, especially when accompanied by symptoms such as low libido, fatigue, or decreased muscle mass, may suggest hypogonadism and require further evaluation.

Some experts may also recommend using age-specific reference ranges to diagnose testosterone deficiency in men ages 20 to 44 because normal levels of testosterone tend to vary by age.

If your healthcare provider suspects hypogonadism, they may also test your luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels to diagnose either primary or secondary hypogonadism. They may also test your prolactin levels to rule out medical conditions like prolactinoma.

• Primary hypogonadism. This type of hypogonadism indicates privates dysfunction or injury to the privates. It usually presents with elevated LH and FSH levels and low T.

• Secondary hypogonadism. This type of hypogonadism indicates faulty signaling between the brain and testes and presents with low or low-normal LH and FSH levels alongside low T.

Who Needs a Testosterone Test?

You may need a testosterone test if you’re experiencing symptoms of low testosterone.

Common symptoms of low testosterone include:

• Low libido

• ED

• Loss of body hair

• Low energy levels

• Brain fog

• Decreased strength

• Reduced muscle mass

• Increased body fat

• Mood changes

• Gynecomastia (breast growth)

• Low sperm count and quality

Symptoms of high testosterone in men are typically less obvious but may include mood changes (such as aggression or irritability), acne, and increased libido.

Aging and certain health conditions, lifestyle factors, and medications can lead to total testosterone levels outside the normal range.

Causes of low testosterone can include:

• Pituitary gland disorders

• Undescended privates

• Mumps orchitis

• Cancer treatments

• Genetic conditions like Klinefelter syndrome or Kallman syndrome

• HIV

• Obesity

• Obstructive sleep apnea

• Aging

Potential causes of high testosterone include:

• Tumors in your privates, pituitary gland, or adrenal glands

• Use of anabolic steroids or testosterone supplements

Many medical treatments can help boost testosterone production if you’ve been diagnosed with low T. Lifestyle tweaks can also help support your body’s ability to make testosterone.

Some ways to support healthy testosterone include:

• Testosterone replacement therapy (TRT). Testosterone replacement therapy (TRT) is often a first-line treatment for men with low testosterone. It’s available via injections, patches, gels, creams, pellets, and pills. Though highly effective for most men, TRT may cause side effects like low sperm count, infertility, privates shrinkage, hair loss, skin reactions, and acne.

• Selective estrogen receptor agonists (SERMs). SERMS like enclomiphene and clomiphene block estrogen feedback at the hypothalamus and pituitary, which increases LH and FSH and stimulates natural testosterone production. These medications generally preserve sperm production, making them an option for men who want to maintain fertility.

• Lifestyle habits. It may sound basic, but following a healthy diet, getting adequate sleep, exercising regularly, and managing your stress levels can affect your hormonal health. Learn more about increasing your testosterone naturally.