Testosterone test: what it measures, normal levels by age, and how to get tested

Testosterone is the main androgen — the hormone behind muscle mass, bone density, red blood cell production, body hair, libido and sperm production in men, and a smaller but real contributor to energy, mood and sexual function in women. It is made mainly in the testes (men) and in the ovaries and adrenal glands (women), under the direction of two pituitary hormones, LH and FSH.

About 98% of the testosterone in blood is attached to proteins: tightly to sex hormone-binding globulin (SHBG) and loosely to albumin. Only the remaining 1–3% is free. A total testosterone test counts all of it — bound and free — in nanograms per deciliter (ng/dL). A free testosterone test estimates just the unbound fraction, and bioavailable testosterone adds back the loosely bound albumin portion, which tissues can also use.

Total testosterone is the test guidelines start with because it is the most standardized and reproducible measurement. Free and bioavailable values matter when SHBG is unusually high or low, because then the total can look normal while the amount actually reaching tissues is not, or the reverse.

Low testosterone symptoms in men build gradually and are shared with poor sleep, depression, obesity and ordinary aging, which is why guidelines ask for both symptoms and two low morning measurements before a diagnosis:

High testosterone in men is rare outside testosterone therapy or anabolic-steroid use and shows up as acne and oily skin, mood swings or aggression, shrinking testes, fluid retention, a high red blood cell count and worsening sleep apnea. In women, high testosterone — most often from polycystic ovary syndrome — causes irregular periods, acne, excess facial or body hair, thinning scalp hair and difficulty conceiving.

Testosterone peaks in the morning and falls through the day, and acute illness, poor sleep or a recent heavy meal can lower it transiently, which is why a low result is repeated on a separate morning before it is called low. Free testosterone and SHBG clarify a borderline total.

The Endocrine Society recommends testing men who have symptoms or signs consistent with testosterone deficiency rather than screening men who feel well. The symptoms that most specifically point to low testosterone are reduced libido, fewer spontaneous erections and erectile dysfunction, loss of body hair, very small or shrinking testes, infertility and hot flashes. Less specific but common reasons to test include persistent fatigue, low mood, poor concentration, loss of muscle and gain of fat, and reduced bone density.

Certain conditions raise the chance that a symptomatic man has a truly low level: obesity, type 2 diabetes, chronic opioid or glucocorticoid use, HIV with weight loss, pituitary disease, prior chemotherapy or radiation to the testes, and known osteoporosis. Men already on testosterone therapy are tested to confirm the dose keeps them in the mid-normal range.

In women, testosterone is measured for a different set of reasons: excess hair growth on the face or body (hirsutism), stubborn adult acne, scalp hair thinning with a male pattern, irregular or absent periods and a suspected diagnosis of polycystic ovary syndrome (PCOS). A very high level in a woman, or symptoms that appeared rapidly, prompts a search for an adrenal or ovarian source.

You can get a testosterone test through your own doctor, or order it online from TestWell and walk into a Quest or Labcorp patient service center — a licensed physician reviews the order, and results arrive in your portal, usually within a few business days. Either way, the timing of the draw matters more than where you have it done.

Testosterone follows a daily rhythm that peaks in the early morning and drifts down through the afternoon, most strongly in younger men. Guidelines therefore call for a morning sample, drawn between roughly 7 and 10 AM. Eating also lowers testosterone for a few hours, so a fasting draw gives a cleaner number; water is fine. Avoid testing during an acute illness, right after a night of very poor sleep, or in the 24 hours after unusually intense exercise — all three can push the level down temporarily.

Because the day-to-day swing is large, a single low total testosterone is never the end of the story. The Endocrine Society requires an unequivocally low result on at least two separate morning samples before diagnosing hypogonadism, and adds free testosterone when the total sits near the lower limit or SHBG is likely to be abnormal.

The reference range printed on most US lab reports for adult men — 264 to 916 ng/dL — comes from a 2017 harmonization study of healthy, non-obese men aged 19 to 39 across several large cohorts, with results calibrated to the CDC's reference method. Some labs still use older, wider ranges (for example 300 to 1,000 ng/dL), so the number on your report should always be read against the range printed next to it.

Levels fall gradually with age — on the order of 1% a year after the thirties — and obesity, diabetes and chronic illness push them lower still, which is why an older man's result is judged partly against how he feels rather than purely against a range derived from young men. In women, total testosterone is roughly a tenth of male values, peaks in the twenties and declines through the reproductive years and after menopause. Children and adolescents have their own age- and puberty-stage ranges and are not covered by the table below.

Start with total. It is the measurement every guideline threshold is written for, and for most men it answers the question. Free testosterone earns its place when the total is borderline or when something is known to distort SHBG. Obesity, type 2 diabetes, hypothyroidism, nephrotic syndrome and glucocorticoids lower SHBG, so the total can under-represent the free fraction; aging, liver disease, hyperthyroidism, HIV, anticonvulsants and estrogens raise SHBG, so a normal-looking total can hide a low free level.

How the free value is produced matters. Equilibrium dialysis is the reference method but is slow and expensive. The widely used alternative is a calculated free testosterone from total testosterone, SHBG and albumin — the same math behind TestWell's free testosterone calculator. Direct 'analog' immunoassays for free testosterone are inexpensive but inaccurate, and the Endocrine Society advises against relying on them.

Time of day is the biggest controllable factor: an afternoon draw can read 20–30% below a morning one in a younger man. Food, sleep deprivation, acute illness and heavy exercise in the previous day each lower the level for hours. Chronic factors include obesity, uncontrolled diabetes, heavy alcohol use, opioids, glucocorticoids and anabolic steroid use, which suppresses the body's own production.

Laboratory method also matters. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is the reference method, and the one to prefer at the low concentrations seen in women and children, where older immunoassays are least reliable. Quest and Labcorp both offer LC-MS/MS total testosterone; the method is printed on the report.

A low result is repeated on another morning, ideally fasting, before it is called low. If it is confirmed, the usual next tests are LH and FSH, which show whether the problem is in the testes (high LH/FSH — primary hypogonadism) or in the pituitary and hypothalamus (low or inappropriately normal LH/FSH — secondary hypogonadism). Prolactin, iron studies (to look for hemochromatosis), a check of other pituitary hormones and, in selected cases, pituitary imaging follow when the pattern points to a central cause.

A high result in a man is most often explained by testosterone therapy or supplements; without those, a clinician looks for a testicular or adrenal source. In a woman, a high level leads to DHEA-S, 17-hydroxyprogesterone, prolactin and TSH, and to a PCOS evaluation, with imaging when levels are very high or symptoms progressed quickly.

Testosterone therapy is a decision for a clinician who has confirmed the diagnosis, looked for the cause and discussed the risks; it is not started from a single online result. The interpretation sections below cover the common causes, symptoms and next steps for high and low readings in more detail.