Free + Total Testosterone
The Free + Total Testosterone test measures both the total circulating pool and the unbound biologically active fraction of testosterone. It is the cornerstone assessment for male hypogonadism, investigation of low libido, erectile dysfunction, and fatigue, and monitoring of testosterone replacement.
2
Biomarkers
Blood (serum)
Sample
1–3 business days
Turnaround
No
Fasting
What is the Free & Total Testosterone test?
The Free + Total Testosterone test measures both the total circulating pool and the unbound, biologically active fraction of testosterone. It is the cornerstone biochemical assessment for male hypogonadism and is ordered to investigate symptoms such as low libido, erectile dysfunction, fatigue, loss of muscle mass, and mood disturbance, as well as to screen for androgen deficiency in men with type 2 diabetes, obesity, or chronic opioid use. Measuring both fractions provides a more complete picture than total testosterone alone, because binding-protein abnormalities can dissociate total from free levels. When SHBG is low — as in obesity, metabolic syndrome, and hypothyroidism — total testosterone underestimates androgen activity; when SHBG is high — as with ageing, hyperthyroidism, or oestrogen therapy — total testosterone overestimates it. Free testosterone, whether measured directly or calculated from total testosterone and SHBG, reflects true androgen bioavailability and is the preferred marker when total testosterone is equivocal or SHBG disturbance is suspected.
What does the Free & Total Testosterone test measure?
Total testosterone represents the sum of circulating hormone bound to sex hormone-binding globulin (approximately 60%), loosely bound to albumin (approximately 38%), and free (1–2%). It is synthesised predominantly in testicular Leydig cells under luteinising hormone stimulation, with smaller adrenal contributions in both sexes. Secretion follows a diurnal rhythm, peaking in the early morning and declining through the day, and production declines progressively with ageing.
Total testosterone is the first-line biochemical marker for male hypogonadism and is used to investigate low libido, erectile dysfunction, fatigue, reduced muscle mass, and infertility. Because the majority is protein-bound, total testosterone can be misleading when SHBG is abnormal — obesity and metabolic syndrome lower SHBG and total testosterone, while ageing and hyperthyroidism raise SHBG, potentially masking low free hormone. For this reason total testosterone is most informative when measured alongside free testosterone or calculated free testosterone.
Free testosterone is the unbound fraction that diffuses freely into cells and exerts direct androgenic and anabolic effects. It represents only 1–2% of total circulating testosterone but is the biologically active pool. Free testosterone rises and falls with total testosterone but is also influenced independently by SHBG concentration — when SHBG increases, free testosterone falls even if total remains stable, and vice versa.
Free testosterone is the best single biochemical marker of androgen bioactivity and is particularly valuable when SHBG is abnormal or when total testosterone is borderline but symptoms are present. Direct free testosterone immunoassays are widely available but less accurate than equilibrium dialysis or calculated free testosterone; practitioners should know which method their laboratory employs. Free testosterone is used to diagnose hypogonadism, to monitor testosterone replacement therapy, and to investigate androgen excess in women.
Why is the Free & Total Testosterone test ordered?
- Investigation of suspected male hypogonadism in patients with low libido, erectile dysfunction, fatigue, reduced muscle mass, or depressed mood
- Screening for androgen deficiency in men with type 2 diabetes, obesity, metabolic syndrome, or chronic opioid therapy
- Evaluation of infertility, particularly when sperm count or quality is reduced and hypogonadism is suspected
- Baseline and monitoring during testosterone replacement therapy, to confirm adequate dosing and avoid supraphysiological levels
- Assessment of delayed puberty or failure of pubertal progression in adolescent males
- Investigation of androgen excess in women (hirsutism, virilisation), though free testosterone is more often calculated than directly measured in this context
- Work-up of unexplained osteoporosis or low bone density in men, where hypogonadism is a common secondary cause
- Evaluation of borderline total testosterone results when clinical suspicion for hypogonadism remains high, particularly in the presence of obesity or other conditions affecting SHBG
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Phlebotomy via LabCorp. Morning collection (07:00–10:00) is strongly recommended, particularly in men under 50, to capture peak testosterone and minimise diurnal variation. Avoid testing during acute illness.
Specimen requirements
Minimum 1 mL serum (gel separator acceptable). Separate from cells and freeze if not assayed promptly. Note the time of collection for interpretation. Specify assay methodology (immunoassay vs LC-MS/MS for total testosterone; direct vs calculated free testosterone) if known.
What can affect Free & Total Testosterone results?
Testosterone follows a pronounced diurnal rhythm, highest in the early morning (07:00–10:00) and declining by 20–30% through the afternoon. Guidelines recommend morning collection for diagnostic accuracy, particularly in younger men; the diurnal amplitude flattens with age.
Adiposity lowers SHBG and suppresses gonadotrophin secretion, reducing both total and free testosterone. Weight loss often restores levels, so distinguishing primary hypogonadism from obesity-related suppression is a clinical judgement.
Critical illness, surgery, and chronic conditions (renal failure, cirrhosis, HIV) lower testosterone through central suppression and altered binding-protein metabolism. Test after recovery or interpret in context.
Chronic opioid use profoundly suppresses the hypothalamic–pituitary–gonadal axis; glucocorticoids lower testosterone; exogenous androgens and anabolic steroids suppress endogenous production, rendering total and free testosterone uninterpretable during use.
Immunoassays for testosterone (especially free testosterone) are less accurate than LC-MS/MS or equilibrium dialysis. Direct free testosterone immunoassays often overestimate the true value; calculated free testosterone (from total testosterone, SHBG, and albumin) is more reliable when gold-standard methods are unavailable.
Hyperthyroidism raises SHBG, increasing total but lowering free testosterone; hypothyroidism has the opposite effect. Correct thyroid dysfunction before final interpretation of androgen status.
What do Free & Total Testosterone results mean?
Elevated
Elevated total and free testosterone in men is uncommon and may suggest exogenous androgen use (therapeutic or supra-physiological), androgen-secreting tumours (testicular or adrenal, though rare), or assay interference. In women, elevated free testosterone indicates androgen excess — polycystic ovary syndrome, congenital adrenal hyperplasia, or virilising tumours. Confirm with repeat testing and correlate clinically.
Normal
Normal total and free testosterone do not exclude clinically significant symptoms, particularly in borderline cases or when SHBG is abnormal. Interpretation must be clinical — symptoms, repeat testing (especially morning samples), and gonadotrophin levels guide management more than a single normal result.
Reduced
Low total and free testosterone in symptomatic men defines biochemical hypogonadism. Primary hypogonadism (testicular failure) presents with elevated LH and FSH; secondary (central) hypogonadism shows low or inappropriately normal gonadotrophins. Common causes include ageing, obesity, type 2 diabetes, chronic opioid or glucocorticoid therapy, Klinefelter syndrome, and pituitary disease. Isolated low total testosterone with normal free testosterone suggests SHBG abnormality rather than true androgen deficiency.
Note: Testosterone must be measured in the morning (07:00–10:00) to minimise diurnal variation, particularly in men under 50. A single low result should be confirmed with repeat testing before diagnosis. Reference intervals are assay-specific and age-dependent; LC-MS/MS is preferred over immunoassay for accuracy. Free testosterone is best measured by equilibrium dialysis or calculated from total testosterone and SHBG; direct immunoassays are less reliable. Always interpret testosterone alongside LH, FSH, and clinical context to distinguish primary from secondary hypogonadism and to assess the need for further pituitary or testicular investigation.
Frequently asked questions
Total testosterone reflects the entire circulating pool, but most is protein-bound and biologically inactive. Free testosterone is the unbound fraction that exerts androgenic effects. Measuring both accounts for SHBG abnormalities — obesity lowers SHBG and total testosterone, while ageing raises SHBG, potentially masking low free hormone. Together they provide a complete picture of androgen status.
How to access the Free & Total Testosterone test
The Free & Total Testosterone reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Bhasin S, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2018)
- Mulhall JP, et al. Evaluation and management of testosterone deficiency: AUA guideline. J Urol. (2018)
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. (1999)
- Travison TG, et al. Harmonized reference ranges for circulating testosterone levels in men of four cohort studies in the United States and Europe. J Clin Endocrinol Metab. (2017)
- Rosner W, et al. Position statement: utility, limitations, and pitfalls in measuring testosterone — an Endocrine Society position statement. J Clin Endocrinol Metab. (2007)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.