Guide to Free Testosterone

WRITTEN BY

The Levels Team

Updated: 05/22/2025|12 min read

Summary

Free testosterone is the small but biologically active portion of total testosterone that is not bound to carrier proteins in the blood. Testing it can provide a more accurate picture of hormonal status than total testosterone alone.

Why It Matters

Testosterone is essential for numerous bodily functions in both men and women, though men naturally have significantly higher levels. In men, testosterone drives the development of male sexual characteristics during puberty, including genital growth, voice deepening, and facial/body hair growth. It maintains muscle mass, bone density, red blood cell production, and sexual function throughout life. In women, testosterone is present in much smaller amounts. But it contributes to energy levels, muscle maintenance, bone health, and sexual function.

When testosterone enters your bloodstream, most of it binds tightly to sex hormone-binding globulin (SHBG), while another portion loosely binds to albumin. Only about 2--4 percent remains unbound as free testosterone. This free portion is the most biologically active form, readily available to enter cells and trigger testosterone's effects.

Measuring free testosterone is valuable because total testosterone levels might appear normal while free testosterone is abnormal. This can happen when SHBG levels are unusually high or low, altering the amount of available testosterone without changing the total amount. Conditions that increase SHBG (like hyperthyroidism, chronic liver disease, or aging) can decrease free testosterone despite normal total levels because more testosterone gets tied up and isn't available to do its job. Conversely, conditions that decrease SHBG (like obesity, insulin resistance, or polycystic ovary syndrome---PCOS) can increase free testosterone despite normal total levels.

Free testosterone helps evaluate symptoms of testosterone deficiency or excess, including sexual dysfunction, infertility, irregular menstruation, excessive hair growth in women, and certain developmental issues. It's also valuable for monitoring hormone replacement therapy and identifying subtle hormonal imbalances that might be missed by total testosterone testing alone.

Associated Symptoms

Free testosterone levels themselves are laboratory findings rather than medical conditions. However, abnormal levels may be associated with certain symptoms that could indicate underlying health conditions.

In men, symptoms that may indicate low free testosterone include:

• Decreased sex drive and reduced sexual function (may indicate hypogonadism, age-related decline, or chronic disease)
• Fatigue and low energy (can occur in male hypogonadism, chronic illness, or depression)
• Decreased muscle mass and increased body fat (may suggest long-term testosterone deficiency)
• Mood changes, including depression or irritability (could indicate hypogonadism or other hormonal imbalances)
• Reduced body and facial hair (may be seen in more severe or prolonged testosterone deficiency)
• Decreased bone density and increased fracture risk (can result from long-term testosterone deficiency)

In men, symptoms that may indicate high free testosterone include:

• Excessive sex drive and aggressive behavior (could suggest anabolic steroid use or rarely, testosterone-producing tumors)
• Acne and oily skin (can occur with steroid use or during puberty)
• Early male pattern baldness (in genetically predisposed people)
• In young boys: early puberty signs before age 9 (may indicate precocious puberty requiring evaluation)

In women, symptoms that may indicate low free testosterone include:

• Decreased sexual desire and satisfaction (may suggest ovarian insufficiency or hypopituitarism)
• Fatigue and reduced energy (can occur in many hormonal conditions)
• Loss of muscle tone and strength (may be associated with aging, menopause, or adrenal insufficiency)
• Thinning hair (may occur with overall hormonal imbalances)

In women, symptoms that may indicate high free testosterone include:

• Irregular or absent menstrual periods (potential sign of PCOS or other hormonal imbalances)
• Excessive facial and body hair growth (hirsutism, may suggest excess androgens from PCOS, adrenal disorders, or rarely tumors)
• Acne, particularly along the jawline and chin (can occur in PCOS and other androgen-excess conditions)
• Male-pattern hair loss or thinning (may suggest significant androgen excess)
• Deepening voice, increased muscle mass, or clitoral enlargement (more severe symptoms that may indicate congenital adrenal hyperplasia or androgen-secreting tumors)

Many of these symptoms can be caused by conditions unrelated to testosterone levels. The severity and combination of symptoms vary widely among people. Proper diagnosis requires comprehensive evaluation, including hormone testing, physical examination, and sometimes imaging studies or genetic testing.

Clinical Ranges

Female:

• 18-69 Years: 0.1-6.4 pg/mL
• 70-89 Years: 0.2-3.7 pg/mL

Male:

• 18-69 Years: 35.0-155.0 pg/mL
• 70-89 Years: 30.0-135.0 pg/mL

Lifestyle Factors That Can Impact It

Activities that may increase free testosterone include:

• Maintaining healthy body weight (especially for overweight men)
• Strength training
• Adequate sleep (7--9 hours nightly)
• Zinc-rich foods (oysters, meat, legumes, nuts)
• Vitamin D (from sunlight exposure and diet)

Activities that may decrease free testosterone include:

• Chronic excessive alcohol consumption
• Severe caloric restriction or crash dieting
• Very low-fat diets (less than 15 percent of calories from fat)

Other Factors That Can Impact It

Medical Conditions

• Diabetes and insulin resistance: Lower free testosterone in men through complex hormonal interactions and reduced testicular function
• Bilateral oophorectomy: Surgical removal of both ovaries dramatically decreases free testosterone.
• Bilateral orchiectomy: Surgical removal of both testicles dramatically decreases free testosterone.
• Eating disorders and malnutrition: Reduce free testosterone through disruption of hypothalamic-pituitary signaling and decreased hormone production due to energy deficit
• Turner syndrome: A genetic condition in which the ovaries don't develop
• PCOS: Increases free testosterone in women due to ovarian overproduction and lower SHBG levels from insulin resistance
• Hypothyroidism: Reduces free testosterone by decreasing testosterone production and altering SHBG levels
• Hyperthyroidism: Might decrease free testosterone by increasing SHBG
• Pituitary disorders and tumors: Decrease free testosterone when they affect gonadotropin production, which stimulates testosterone synthesis
• Klinefelter syndrome (XXY genetic pattern): Reduces free testosterone through impaired testicular development and function
• Adrenal insufficiency (Addison's disease), primarily in women.
• Premature menopause: Reduces free testosterone due to earlier-than-expected decline in ovarian function, which significantly decreases androgen production
• Primary ovarian insufficiency: Reduces free testosterone due to impaired ovarian function and diminished androgen production from ovarian tissue
• Chronic liver disease: Reduces testosterone through impaired metabolism of sex hormones and increased sex hormone-binding globulin production
• Chronic kidney disease: Lowers testosterone through disrupted hormonal signaling and increased inflammation

Medications

• Opioid pain medications: Decrease free testosterone through suppression of the hypothalamic-pituitary-gonadal axis
• Glucocorticoids (such as prednisone): Reduce free testosterone through suppression of pituitary hormone production
• Hormonal contraceptives: Decrease free testosterone by suppressing pituitary LH production and increasing sex hormone binding globulin levels
• Chemotherapy and radiation: Reduce free testosterone through direct damage to testicular tissue and disruption of the hormonal signaling pathway
• Medications: Exogenous androgens---like anabolic steroids---can suppress natural testosterone production
• Anabolic steroids: Suppress natural testosterone production while providing synthetic androgens
• Spironolactone (a blood pressure medication): Decreases free testosterone by blocking androgen receptors and reducing production

Testing Accuracy and Stability

Several factors can affect the accuracy of free testosterone testing and are important to consider when interpreting your results.

Factors That Can Affect the Accuracy of Your Test

• The testing method significantly impacts results. Direct measurement by equilibrium dialysis is considered the gold standard but is complex and expensive. Calculated free testosterone from total testosterone and SHBG is more common but less precise.
• Time of day dramatically affects results. Levels are typically highest in the morning and lowest in the evening, especially in younger men.
• Recent sexual activity can temporarily increase free testosterone for 24--48 hours through hormonal feedback loops.
• An acute illness can temporarily decrease levels, making testing during illness potentially misleading.
• Strenuous exercise within 24 hours of testing can either increase levels (short, intense exercise) or decrease levels (prolonged endurance exercise).
• Nutritional status affects results. Fasting may lower levels slightly while severe caloric restriction for several days may reduce levels.
• Stress during blood collection can affect results through acute cortisol release, potentially reducing measured testosterone.

How It Relates to Other Markers

Other tests can provide your doctor insights about your health status when viewed alongside free testosterone results. These tests may include:

• Total testosterone: This test provides context for free testosterone. The relationship between the two helps identify conditions affecting SHBG.
• SHBG: This marker directly affects free testosterone levels. High SHBG reduces free testosterone while low SHBG increases it.
• Albumin: This is the secondary protein carrier for testosterone. Significant albumin abnormalities can affect the bioavailable testosterone fraction.
• Luteinizing hormone (LH): This test helps distinguish primary (testicular/ovarian) from secondary (pituitary/hypothalamic) causes of testosterone abnormalities.
• Follicle-stimulating hormone (FSH): FSH is important for evaluating reproductive function and diagnosing primary gonadal failure.
• Estradiol: The balance between testosterone and estrogen affects many bodily functions.
• Prolactin: Elevated prolactin can suppress testosterone production and cause symptoms similar to low testosterone.

What Results May Mean in the Context of Other Markers

• Low free testosterone with low total testosterone and high LH/FSH: Could suggest primary testicular failure---testes not producing adequate testosterone despite stimulation.
• Low free testosterone with low total testosterone and low/normal LH/FSH: May indicate secondary hypogonadism---pituitary or hypothalamic issue failing to signal the testes.
• Low free testosterone with normal total testosterone and high SHBG: may suggest SHBG-related functional testosterone deficiency---total amount adequate but too much is bound and unavailable.
• High free testosterone with high total testosterone in women: May indicate PCOS, adrenal hyperplasia, or testosterone-producing tumors.
• High free testosterone with normal total testosterone and low SHBG: Functional testosterone excess due to increased availability---can occur in insulin resistance and obesity.
• Decreasing free testosterone with age in men: Normal age-related decline, but rate and symptoms vary widely between people.
• Changes in free testosterone with age in women: Menopausal status may impact testosterone levels.

Follow-up Considerations

If your free testosterone levels are abnormal, your healthcare provider may work with you on a plan to address any levels that are out of range. Here are some recommendations they might make. You should always speak to your doctor if you have medical questions or before making medical decisions.

When Re-Testing May be Appropriate

• Initial abnormal result: Often repeated to confirm findings, typically 2--4 weeks apart
• After starting testosterone therapy: 2--3 months, then every 6--12 months
• After making significant lifestyle changes: 3--6 months
• During weight loss: Every 3--6 months with significant weight change
• Monitoring known conditions: As directed, typically every 6--12 months
• With changing symptoms: As needed to reassess status

Additional Testing Your Doctor May Consider

• Thyroid function tests
• HbA1c and fasting glucose (insulin resistance evaluation)
• Bone density scan if chronically low testosterone
• Semen analysis for fertility concerns
• Pituitary imaging if secondary hypogonadism suspected
• Genetic testing in certain cases
• Iron studies: Anemia can affect testosterone and vice versa: low testosterone can increase risk for anemia for both men and women
• Sleep study if sleep apnea is suspected (can lower testosterone)
• Comprehensive metabolic panel for liver and kidney function

When Additional Care May be Warranted

• Significantly abnormal levels (>50 percent outside reference range)
• Infertility concerns
• Delayed or precocious puberty in adolescents
• Rapidly developing symptoms of hormone imbalance
• Free testosterone abnormalities with serious comorbidities (cardiovascular disease, diabetes)
• Extremely high testosterone in women (possible tumors)
• Bone density concerns with low testosterone
• Development of adverse effects from testosterone therapy
• Suspected drug-induced hormonal changes

Bibliography