Free Testosterone
Free testosterone is the small fraction (about 1–2%) of total testosterone that circulates unbound and can enter cells to act. It is the physiologically active form. Free testosterone is most useful when SHBG is abnormal (obesity, diabetes, older age, liver disease, estrogen therapy) — in those settings, total testosterone can be normal while free testosterone is low and symptomatic. Direct measurement is difficult; calculated or equilibrium dialysis-based free testosterone is used.
Reference Ranges
Male
47 – 244
pg/mL
Female
0.3 – 5
pg/mL
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low free testosterone in a man with hypogonadal symptoms confirms clinically meaningful androgen deficiency, even if total testosterone is borderline. Evaluation should cover pituitary function (LH, FSH, prolactin), pituitary imaging if central, and reversible causes (obesity, sleep apnea, opioid use). In women, low free testosterone has been implicated in hypoactive sexual desire disorder.
What High Levels Mean
In men, elevated free testosterone often indicates exogenous anabolic steroid use; it can also be seen in polycythemia and some testicular or adrenal conditions. In women, elevated free testosterone with hirsutism supports PCOS; very high levels (particularly with rapid onset of virilization) raise suspicion for an androgen-secreting tumor and require urgent evaluation.
Frequently Asked Questions
When should free testosterone be measured?
When SHBG is likely abnormal: older men, obese patients, diabetes, chronic liver disease, hyperthyroidism, oral estrogen users, and women being evaluated for PCOS. In a young, lean male, total testosterone is usually sufficient. Measuring free testosterone routinely along with total is common but often unnecessary.
What is the best method for free testosterone?
Equilibrium dialysis is the gold standard. Most labs use calculated free testosterone from total testosterone + SHBG + albumin — reliable if the lab uses a validated equation. Direct free testosterone assays (analog immunoassays) are unreliable and should be avoided. Always check what method your lab uses.
Can free testosterone guide replacement therapy in men?
Yes. In men on testosterone replacement, target total testosterone is mid-normal range with free testosterone in normal range; these track therapy. Symptom response is the primary outcome — numerical targets alone without symptom improvement are not a reason to intensify therapy, and levels must be interpreted with time of sampling and formulation kinetics in mind.
Related Hormones tests
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Pancreatic hormone that controls blood sugar.
µIU/mLHormonesHOMA-IR (Insulin Resistance Index)
Calculated index that estimates insulin resistance.
indexHormonesBeta-hCG (Human Chorionic Gonadotropin)
Pregnancy hormone — also a tumor marker for certain cancers.
mIU/mLHormonesSex Hormone Binding Globulin (SHBG)
Protein that binds sex hormones in blood, controlling their availability.
nmol/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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