Testosterone, Free
Free testosterone is the biologically active form of testosterone — the portion not bound to proteins that can freely enter cells and exert hormonal effects. While total testosterone measures all testosterone in your blood, free testosterone reveals how much is actually available to your tissues. This distinction is crucial because SHBG variations can make total testosterone misleading. Testing free testosterone regularly provides the most accurate picture of your bioavailable hormone status.
Free testosterone is the biologically active form of testosterone, the portion not bound to proteins that can freely enter cells and exert hormonal effects. While total testosterone measures all testosterone in your blood, free testosterone reveals how much is actually available to your tissues. This distinction is crucial for understanding your true hormonal status.
Why does this matter? Because SHBG (sex hormone-binding globulin) variations can make total testosterone misleading. Many people experience fatigue, low libido, or mood changes despite having “normal” total testosterone, their free testosterone is actually low, but standard testing missed it. Conversely, some people with “low” total testosterone feel fine because their free testosterone is adequate.
Testing free testosterone, regularly, even when healthy, provides the most accurate picture of your bioavailable hormone status. Regular testing (1-2 times per year) tracks changes over time, catches decline years before symptoms appear, and enables prevention rather than just treatment.
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Key Benefits of Free Testosterone Testing
- Measure bioavailable hormone — Understand how much testosterone is actually active in your body
- Clarify borderline results — Determine true hormonal status when total testosterone is near normal limits
- Account for SHBG variations — Get accurate assessment despite SHBG changes from aging, obesity, or thyroid function
- Explain symptom-test discrepancies — Identify why you have symptoms despite “normal” total testosterone
- Guide treatment accurately — Confirm true testosterone deficiency before hormone therapy
- Monitor therapy precisely — Track bioavailable testosterone during treatment
- Optimize metabolic assessment — Free testosterone often correlates better with metabolic health than total
- Most accurate when paired with total testosterone — Combined testing provides complete hormonal picture
What Does Free Testosterone Measure?
Free testosterone measures the unbound testosterone circulating in your bloodstream — the portion not attached to carrier proteins.
Understanding Testosterone Binding:
Testosterone doesn’t circulate alone in blood. Most binds to carrier proteins:
SHBG-bound (~60-70%) — Tightly bound to sex hormone-binding globulin (SHBG). This testosterone is biologically inactive—it cannot enter cells or exert hormonal effects. SHBG binding is so tight that this testosterone is essentially “locked away.”
Albumin-bound (~30-40%) — Loosely bound to albumin protein. This testosterone can dissociate from albumin and become available when needed. Combined with free testosterone, this forms “bioavailable testosterone.”
Free (~2-3%) — Completely unbound. This testosterone freely diffuses into cells, binds to androgen receptors, and triggers hormonal responses. Despite being only 2-3% of total, this is the portion that matters for most physiological effects.
Why Free Testosterone is Critical:
Because free testosterone is the bioactive form, it often correlates better with symptoms and metabolic health than total testosterone. When SHBG levels are abnormal, total testosterone can be misleading:
High SHBG (from aging, hyperthyroidism, liver disease, estrogen use) — Binds more testosterone, lowering free testosterone even when total appears normal. Result: symptoms of testosterone deficiency despite “normal” total.
Low SHBG (from obesity, metabolic syndrome, hypothyroidism, insulin resistance) — Less testosterone is bound, so free testosterone may be normal even when total appears low. Result: few symptoms despite “low” total.
Free testosterone measurement cuts through this confusion, showing actual bioavailable hormone regardless of SHBG variations.
How Free Testosterone is Measured:
Direct measurement — Specialized assays directly measure free testosterone. More accurate but expensive and not widely available.
Calculated free testosterone — Most common approach. Calculated from total testosterone and SHBG measurements using validated equations. Accuracy depends on reliable total testosterone and SHBG measurements.
Both approaches provide valuable clinical information when interpreted properly.
Why Free Testosterone Testing Matters
More Accurate Than Total Alone
Free testosterone often reflects true hormonal status better than total testosterone, particularly when SHBG is abnormal. Many men with symptoms have normal total but low free testosterone due to elevated SHBG. Conversely, some obese men have low total but normal free testosterone with minimal symptoms due to low SHBG. Free testosterone identifies these situations, guiding appropriate treatment.
Explains Symptom-Test Discrepancies
When symptoms suggest testosterone deficiency but total testosterone is normal (or vice versa), free testosterone often clarifies the situation. This is especially common in older men (SHBG increases with age) and obese men (SHBG decreases with obesity). Free testosterone measurement resolves these discrepancies.
Better Metabolic Correlation
Studies show free testosterone correlates better with metabolic health markers—insulin resistance, visceral fat, diabetes risk—than total testosterone. Free testosterone may be a superior marker for metabolic syndrome and cardiovascular risk assessment.
More Precise Treatment Monitoring
During testosterone replacement therapy, monitoring free testosterone ensures therapy achieves adequate bioavailable hormone levels, not just normal total testosterone. This leads to better symptom resolution and fewer side effects from over-replacement.
What Can Affect Free Testosterone Levels?
SHBG Variations (Primary Factor)
Because SHBG binding determines how much testosterone remains free, anything affecting SHBG profoundly impacts free testosterone:
Factors Increasing SHBG (lowering free testosterone):
- Aging — SHBG rises progressively with age in men
- Hyperthyroidism — Excess thyroid hormone elevates SHBG
- Liver disease — Cirrhosis increases SHBG production
- Estrogen exposure — Oral estrogens, pregnancy raise SHBG
- HIV infection — Often associated with elevated SHBG
- Anticonvulsants — Some medications increase SHBG
Factors Decreasing SHBG (raising free testosterone relative to total):
- Obesity — Strong inverse correlation; more fat = lower SHBG
- Insulin resistance and metabolic syndrome — Suppress SHBG production
- Hypothyroidism — Low thyroid hormone reduces SHBG
- Androgens — Testosterone replacement and anabolic steroids lower SHBG
- Growth hormone — Suppresses SHBG
- Glucocorticoids — Prednisone lowers SHBG
Same Factors Affecting Total Testosterone
Free testosterone is also affected by everything that changes testosterone production:
Low Free Testosterone:
- Aging — Combined effect: testosterone production declines AND SHBG rises
- Obesity — Suppresses testosterone production (though partially offset by lower SHBG)
- Type 2 diabetes — 30-40% of diabetic men have low free testosterone
- Chronic opioid use — Profoundly suppresses all testosterone
- Pituitary/testicular disorders — Reduce testosterone production
- Chronic illness — Kidney disease, liver cirrhosis, HIV suppress testosterone
- Poor sleep — Sleep deprivation and sleep apnea lower testosterone
- Chronic stress — Elevated cortisol suppresses testosterone
High Free Testosterone:
- Testosterone replacement therapy — Intentionally raises free testosterone
- Anabolic steroid use — Dramatically elevates free testosterone
- PCOS in women — Elevates both total and free testosterone
- Androgen-secreting tumors — Rare cause of elevated testosterone
Lifestyle Factors
The good news: lifestyle significantly impacts free testosterone. Weight loss is particularly powerful—it raises testosterone production AND lowers SHBG, dramatically increasing free testosterone in overweight individuals. Resistance training optimizes production. Sleep and stress management support healthy hormone levels. These interventions can improve free testosterone 20-40% in appropriate individuals.
When Should You Test Free Testosterone?
Preventive Testing: Before Symptoms Appear
Regular testing (annually or twice yearly) provides valuable information even without symptoms. It establishes your personal baseline, reveals your aging trajectory, and catches decline 5-10 years before symptoms develop. This preventive approach is particularly valuable for men over 40 and women approaching menopause. Prevention through early detection is more effective than treating established deficiency.
Men Should Consider Free Testosterone If:
Borderline Total Testosterone:
When total testosterone is near the lower limit of normal (or just below) but symptoms are present, free testosterone determines true hormonal status.
Symptoms Despite Normal Total:
Low libido, erectile dysfunction, fatigue, or other symptoms suggesting testosterone deficiency when total testosterone is normal—often due to elevated SHBG.
Obesity or Metabolic Syndrome:
Low SHBG in obesity means total testosterone may underestimate bioavailable hormone. Free testosterone provides more accurate assessment.
Older Men (>60):
SHBG rises with age, making free testosterone particularly important for accurate assessment in older men.
Monitoring Testosterone Replacement:
Free testosterone ensures therapy achieves adequate bioavailable hormone, not just normal total testosterone.
Women May Benefit If:
Evaluating PCOS:
While total testosterone is primary marker, free testosterone provides additional information about androgen excess severity.
Symptoms with Normal Total:
Similar to men—symptoms potentially from androgens despite normal total testosterone.
Testing Requirements
Morning Testing for Men:
Although free testosterone has less pronounced diurnal variation than total, morning testing (7-11 AM) remains recommended for consistency and comparison to reference ranges.
Requires Total Testosterone and SHBG:
If using calculated free testosterone (most common approach), both total testosterone and SHBG must be measured simultaneously.
Repeat Testing:
Like total testosterone, confirm abnormal free testosterone results with repeat testing before diagnosis or treatment decisions.
Understanding Your Free Testosterone Results
Your results will include laboratory-specific reference ranges that vary by age, sex, and testing method. The most meaningful comparisons are your own results over time using the same lab.
Interpreting Results in Context
Free testosterone is most meaningful alongside total testosterone and SHBG:
Low free with normal total testosterone suggests elevated SHBG is binding excess testosterone. Common with aging, liver disease, hyperthyroidism. Treatment may help even though total looks “normal.”
Low free with low total testosterone confirms true testosterone deficiency—clearest indication for evaluation and potential treatment.
Normal free with low total testosterone suggests low SHBG from obesity or insulin resistance. Bioavailable hormone may be adequate. Lifestyle intervention often helps both numbers and underlying health.
Next Steps If Abnormal
Low free testosterone should be confirmed with repeat testing. Additional evaluation includes LH/FSH (to distinguish causes), prolactin (to screen for pituitary tumors), and assessment of underlying conditions. Treatment decisions consider symptoms, severity, and underlying causes.
High free testosterone in women requires evaluation for PCOS, adrenal androgens, and rarely imaging if tumor suspected.
What to Do About Abnormal Free Testosterone
For Men with Low Free Testosterone
Lifestyle Interventions:
Weight loss — Powerfully effective for obese men. Raises testosterone production AND lowers SHBG, increasing free testosterone more than total testosterone alone. 10 kg weight loss can dramatically improve free testosterone.
Resistance training — 3-4 weekly sessions optimize testosterone production and improve free testosterone.
Sleep optimization — 7-9 hours nightly. Treat sleep apnea if present.
Address thyroid dysfunction — If hyperthyroidism is elevating SHBG, treating it normalizes SHBG and improves free testosterone.
Nutritional optimization — Adequate healthy fats, protein, micronutrients support testosterone production.
Testosterone Replacement Therapy:
For confirmed low free testosterone with symptoms, testosterone replacement effectively raises both total and free testosterone, improving libido, erectile function, energy, mood, muscle mass, and bone density.
Free testosterone monitoring during therapy ensures adequate bioavailable hormone levels are achieved.
See our Low Testosterone article for comprehensive treatment information.
For Those with High SHBG (Normal Total, Low Free)
When total testosterone is normal but free is low due to high SHBG:
Address SHBG causes — Treat hyperthyroidism if present, address liver disease, discontinue estrogen if appropriate.
Consider treatment — Some men with normal total but low free testosterone and symptoms may benefit from testosterone replacement, though this is more controversial than treating low total and free together.
Monitoring
During testosterone replacement: Check free testosterone 3-6 months after starting, then periodically to ensure therapy achieves target bioavailable levels.
After lifestyle changes: Retest in 3-6 months. Weight loss effects on free testosterone can be dramatic.
Free Testosterone and Related Health Conditions
Free testosterone connects to health conditions across multiple systems. Understanding these connections helps explain why this biomarker matters for comprehensive health assessment.
Thyroid Disorders
Hyperthyroidism raises SHBG, lowering free testosterone. Hypothyroidism lowers SHBG, sometimes masking low testosterone production.
Metabolic Health
Prediabetes and Type 2 Diabetes: Low free testosterone in men increases diabetes risk 2-4 fold, while diabetes itself suppresses testosterone—creating a vicious cycle. Free testosterone often correlates better with insulin resistance than total testosterone.
Metabolic Syndrome and Obesity: Each component of metabolic syndrome associates with lower free testosterone. Obesity suppresses production while also lowering SHBG. Weight loss powerfully improves levels through both mechanisms.
Women’s Hormonal Health
PCOS: Elevated free testosterone is central to PCOS and often correlates better with metabolic complications than total testosterone.
Menopause: Free testosterone declines during menopause as production decreases and SHBG rises with age. This contributes to decreased libido, fatigue, and muscle loss alongside estrogen deficiency.
Men’s Health
Low Testosterone: Free testosterone is the functional marker of testosterone deficiency. Many symptomatic men have low free testosterone despite borderline total.
Erectile Dysfunction and Infertility: Free testosterone is necessary for erectile function and sperm production. Evaluation of both conditions includes free testosterone assessment.
Bone, Muscle, and Aging
Osteoporosis: Low free testosterone increases fracture risk in both men and women. Men with unexplained osteoporosis should have testosterone assessed.
Sarcopenia and Frailty: Age-related muscle loss accelerates with declining free testosterone. Maintaining adequate levels supports physical function and independence in aging.
Mental Health and Sleep
Depression: Low free testosterone independently associates with depression in men. Some treatment-resistant depression cases involve undiagnosed testosterone deficiency.
Sleep Apnea: Bidirectional relationship — sleep apnea lowers testosterone, and low testosterone may worsen sleep apnea. Men with either condition should be screened for the other.
Why Free Testosterone is Part of Your Comprehensive Hormone Assessment
Reveals True Bioavailable Hormone — Shows what’s actually active in your body, not just total production.
Clarifies Discrepancies — Resolves conflicts between symptoms and total testosterone results.
Better Metabolic Marker — Often correlates better with metabolic health than total testosterone.
Optimizes Treatment — Ensures therapy achieves adequate bioavailable testosterone for symptom resolution.
Essential Pairing with Total — Free testosterone is most valuable when interpreted alongside total testosterone and SHBG.
Related Biomarkers Often Tested Together
For accurate free testosterone assessment:
- Total testosterone (essential for calculated free testosterone)
- SHBG (essential for calculated free testosterone)
- LH and FSH (identify causes of abnormal levels)
- Clinical symptoms
Total Testosterone
Standard screening test measuring all testosterone. Essential companion to free testosterone. Both should be measured together for complete picture.
SHBG
Protein binding testosterone and controlling free testosterone levels. Essential for calculating free testosterone and understanding why total and free may diverge. SHBG measurement explains discrepancies between total and free testosterone.
LH and FSH
Pituitary hormones regulating testosterone production. Help identify whether low testosterone results from testicular failure (high LH/FSH) or pituitary/hypothalamic dysfunction (low/normal LH/FSH).
Prolactin
Elevated prolactin suppresses testosterone. Screens for pituitary tumors in men with low testosterone.
Estradiol
Testosterone converts to estradiol via aromatase. High estradiol can suppress testosterone production and raise SHBG.
Thyroid Function Tests
Thyroid disorders significantly affect SHBG and free testosterone. TSH, free T4 help explain SHBG abnormalities.
Insulin and Glucose
Insulin resistance lowers both testosterone production and SHBG. Reveals metabolic contributions to hormonal imbalance.
Our Comprehensive Hormone Panel includes free testosterone with these complementary markers for complete assessment.
Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.
Frequently Asked Questions
Total measures all testosterone in your blood; free measures only the unbound, active form (2-3% of total). When SHBG is abnormal—common with aging, obesity, and various conditions—total can be misleading while free reveals true bioavailable hormone. For complete assessment, both should be measured together since neither tells the full story alone.
Yes, this is surprisingly common, especially with elevated SHBG from aging, liver disease, or hyperthyroidism. The high SHBG binds more testosterone, reducing the free fraction even though total looks normal. This explains why many people have clear symptoms of testosterone deficiency despite “normal” total testosterone—their bioavailable hormone is actually low.
Yes. Regular testing establishes your baseline, reveals your aging trajectory, and catches decline years before symptoms appear—when prevention is most effective. This is particularly valuable for men over 40 and women approaching menopause.
For prevention and monitoring: 1-2 times per year to track trends. During active health optimization: every 3-6 months to measure impact. During testosterone treatment: 3-6 months after starting, then 1-2 times annually.
Yes, significantly. Free testosterone directly influences bone density. Low levels increase osteoporosis and fracture risk in both men and women. Men with unexplained bone loss should have testosterone evaluated.
Yes, in specific situations: evaluating androgen excess (PCOS, hirsutism, acne), menopause symptoms like low libido or fatigue, and infertility. Free testosterone often correlates better with symptoms than total testosterone in women.
Yes, substantially. Weight loss is most powerful—improving production AND lowering SHBG. Combined with resistance training, sleep optimization, and stress management, lifestyle changes can improve free testosterone 20-40% or more in appropriate individuals.
With testosterone therapy, levels rise within days to weeks. Symptomatic benefits take longer: libido and mood improve in 3-6 weeks, muscle mass over 6-12 months, bone density over 1-2 years.
References
This article provides comprehensive educational information about polycystic ovary syndrome based on current clinical guidelines and peer-reviewed research. It does not replace personalized medical advice. Consult qualified healthcare professionals for diagnosis and treatment decisions specific to your situation.
Key Sources:
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666-3672.
- Goldman AL, et al. A Reappraisal of Testosterone’s Binding in Circulation. J Clin Endocrinol Metab. 2017;102(2):370-382.
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism. J Clin Endocrinol Metab. 2018;103(5):1715-1744.
