Testosterone Blood Test: Normal Levels, Low & High Explained

The testosterone blood test measures the main androgen hormone — the one that drives libido, muscle mass, bone strength, body hair, and sperm production in men, and that women make in much smaller amounts. A testosterone test is ordered to work up a possible deficiency (hypogonadism, the cause of most "low testosterone" complaints in men) or, in women, an excess that can point to PCOS. The number sounds simple, but reading it well is not: your result swings with the time of day, how much of the hormone is bound versus free, your weight, and your symptoms. This guide explains what the test measures, the normal testosterone levels in ng/dL, the difference between total, free, and bioavailable testosterone, and how doctors actually decide whether a level is "low." Testosterone is part of the broader hormone panel.

Key takeaways

• Testosterone circulates in total, free, and bioavailable forms; a transport protein called SHBG shapes how much is active. Blood is drawn in the morning, when levels peak.¹²
• Indicative total testosterone for adult men is roughly 300 – 1,000 ng/dL; a harmonized reference range puts the lower limit near 264 ng/dL. Women run far lower (~ 15 – 70 ng/dL). Ranges are lab-specific.³⁴
• Low testosterone (hypogonadism) is diagnosed from two low early-morning samples plus symptoms — not a single number. Common thresholds are around 264 – 300 ng/dL.³⁵
• Obesity is a frequent, often reversible cause of low testosterone: weight loss commonly raises it.⁶
• The most accurate assays use LC-MS/MS (mass spectrometry), and free testosterone is best confirmed by equilibrium dialysis or calculated from total testosterone and SHBG.⁷¹
• In women, a high result — with acne, excess hair, or irregular cycles — most often suggests PCOS or another cause of androgen excess.⁸

What is testosterone?

Testosterone is the principal androgen (male sex hormone). In men it is produced mainly by the testes, under the control of two pituitary hormones — LH and FSH — in a feedback loop with the brain. In women, small amounts come from the ovaries and adrenal glands. Beyond its role in sexual development and libido, testosterone supports muscle and bone mass, red blood cell production, body hair, mood, and sperm production.⁴²

Most testosterone in the blood doesn't float free. It travels bound to proteins — tightly to SHBG (sex hormone-binding globulin) and loosely to albumin. Only the unbound (free) fraction, plus the loosely albumin-bound portion, is readily available to tissues; together these make up bioavailable testosterone. That is why a lab measures total testosterone first, and adds free or bioavailable testosterone and SHBG when the clinical picture calls for it.¹ Because secretion follows a daily rhythm and peaks in the early hours, the sample is drawn in the morning. Testosterone is interpreted within the hormone panel.

Why the test is done

A clinician orders a testosterone blood test to:²⁵

• in men: evaluate signs of deficiency — low libido, erectile difficulties, fatigue, loss of muscle mass, low mood, sometimes reduced bone density or anemia — or a fertility problem;
• in women: work up signs of androgen excess — acne, excess facial or body hair (hirsutism), scalp hair thinning, irregular periods — that may suggest PCOS;
• investigate delayed or early puberty in adolescents;
• monitor treatment, whether testosterone replacement in men or anti-androgen therapy in women.

A single value rarely stands alone: it is read together with LH, FSH, prolactin, SHBG, and the person's symptoms.

Total, free and bioavailable testosterone (and SHBG)

This is where the test becomes genuinely nuanced — and where a lot of confusion starts.

• Total testosterone measures everything in the blood: free hormone plus everything bound to SHBG and albumin. It is the standard first-line test and is enough for most people.³
• Free testosterone is the small unbound fraction (roughly 1 – 2% of the total) that is biologically active. Typical adult-male values are about 50 – 210 pg/mL (≈ 5 – 21 ng/dL), but they vary widely by method.⁹
• Bioavailable testosterone adds the loosely albumin-bound portion to the free fraction — the part tissues can actually use.

The reason free and bioavailable testosterone matter is SHBG. When SHBG is high — with aging, liver disease, hyperthyroidism, or estrogen — more testosterone is locked up, so a "normal" total can still leave too little active hormone. When SHBG is low — with obesity, insulin resistance, hypothyroidism, or nephrotic syndrome — total testosterone can read low even though the free fraction is adequate.¹ That is why guidelines advise measuring free (or bioavailable) testosterone when the total sits near the threshold or when SHBG is expected to be abnormal.³

How free testosterone is obtained matters too. The reference method is equilibrium dialysis; a calculated free testosterone (derived from total testosterone and SHBG) is a reasonable, widely used alternative. Direct "analog" immunoassays for free testosterone are considered unreliable and are discouraged.¹⁷

How the test is done

The test is a simple blood draw from a vein in the arm. A few practical points make the result trustworthy:³²

• Timing: blood is drawn in the morning, ideally before 10 a.m., when testosterone is highest. Afternoon samples run lower and can look falsely deficient — a leading cause of misdiagnosis.
• Fasting: many labs prefer a fasting morning sample, because glucose intake can transiently lower testosterone.
• Repeat when low: a low result should be confirmed on a second early-morning sample, since day-to-day variation is real.⁵
• Assay quality: the most accurate measurement uses LC-MS/MS (liquid chromatography–tandem mass spectrometry) or a well-validated immunoassay. Mass spectrometry is preferred at low concentrations — that is, in women, children, and men with borderline levels — where older immunoassays are least reliable.⁷¹

Tell your clinician about any medications, supplements, or recent acute illness, all of which can move the number.

Normal ranges

The values below are indicative reference ranges. They differ markedly by sex, age, time of day, and assay — always trust the interval printed on your report.

Good to know: the U.S. unit is ng/dL (nanograms per deciliter). To convert to the SI unit, multiply by 0.0347 → nmol/L (so 300 ng/dL ≈ 10.4 nmol/L). A modern effort has produced a harmonized reference range from a large U.S. population sample, setting the normal lower limit for young men near 264 ng/dL — but individual labs still differ, which is exactly why a borderline number is never read in isolation.³

Testosterone also declines gradually with age in men, typically by about 1 – 2% per year after the 30s. That slow drift is normal and, on its own, is not "male menopause" or a reason to treat.⁴⁶

Low testosterone (hypogonadism)

Hypogonadism is not defined by a single low number. Both the Endocrine Society and the American Urological Association (AUA) require two unequivocally low early-morning total testosterone measurements combined with consistent symptoms.³⁵ The AUA defines low testosterone as below 300 ng/dL on two morning tests; the Endocrine Society anchors closer to the harmonized 264 ng/dL lower limit. Either way, one afternoon reading is not a diagnosis.

Typical symptoms include reduced libido, erectile difficulties, fatigue, loss of muscle mass and strength, low mood, poor concentration, and sometimes reduced bone density or anemia.³ Once low testosterone is confirmed, LH and FSH help locate the problem:

• Primary hypogonadism — the testes themselves are failing: testosterone low, LH and FSH high. Causes include Klinefelter syndrome, prior injury, chemotherapy, or mumps orchitis.
• Secondary (central) hypogonadism — the pituitary or hypothalamus isn't signaling: testosterone low, LH and FSH low or inappropriately normal. Causes include obesity, pituitary disorders, high prolactin, opioids, and chronic illness.⁵

Obesity deserves special mention: it is one of the most common — and most reversible — causes of a low reading. Excess fat lowers SHBG (dragging total testosterone down) and suppresses the pituitary signal. Weight loss and lifestyle change often raise testosterone, frequently before any medication is warranted.⁶

High testosterone

High testosterone is far more clinically important in women than in men. In women, an elevated level with acne, hirsutism, scalp hair loss, or irregular cycles most often points to polycystic ovary syndrome (PCOS), the leading cause of androgen excess. Other causes include congenital adrenal hyperplasia and, rarely, an androgen-secreting ovarian or adrenal tumor — the latter suggested by a rapid onset or a very high level.⁸⁴

In men, an unexpectedly high result is uncommon and usually reflects exogenous testosterone (prescribed therapy, or non-prescribed anabolic-steroid use) rather than a naturally overactive gland. In adolescents it can signal precocious puberty. Testosterone is always interpreted alongside the rest of the hormone panel.

Factors that affect the result

Several ordinary factors move testosterone or its interpretation, no disease required:¹⁶

• Time of day — the single biggest one; levels peak in the morning and fall by afternoon.
• Age — a slow, expected decline in men after the 30s.
• Body weight — obesity lowers SHBG and total testosterone (often reversibly).
• SHBG shifts — aging, liver or thyroid disease, and estrogen raise SHBG; obesity, insulin resistance, and nephrotic syndrome lower it, each pulling total testosterone with them.
• Acute or chronic illness — serious illness transiently suppresses testosterone, so testing during an acute illness is best avoided.
• Medications — opioids, glucocorticoids, some anticonvulsants, and androgen-deprivation therapy lower it; testosterone therapy raises it.

Report your full context and medications so the result is read correctly.

When to see a doctor

See a clinician if you have persistent symptoms that fit the picture — in men, low libido, erectile difficulties, unexplained fatigue, or loss of muscle mass; in women, new acne, excess hair growth, or irregular periods — rather than reacting to a single borderline number. A confirmed low or high result should be evaluated in context, with the timing, SHBG, free testosterone, LH/FSH, and your symptoms all weighed together. Testosterone therapy is a prescription medication reserved for confirmed, symptomatic hypogonadism under medical supervision — not an over-the-counter "anti-aging" or performance supplement, and over-the-counter "testosterone boosters" have no proven benefit on hormone levels or symptoms.³⁵

Recent research

According to recent publications indexed on PubMed and major guidelines:

• Cardiovascular safety is reassuring. The large randomized TRAVERSE trial (~5,200 middle-aged and older men with hypogonadism and high cardiovascular risk) found testosterone therapy non-inferior to placebo for major adverse cardiac events, while flagging a modest increase in atrial fibrillation — supporting careful monitoring rather than avoidance.¹⁰ A companion analysis found no excess of aggressive prostate cancer, though prostate surveillance remains standard.¹¹
• Obesity is a reversible driver. Recent reviews emphasize that low testosterone in men with obesity is largely explained by lowered SHBG and suppressed central signaling, and is often reversible with weight loss and lifestyle change — frequently the first step before considering therapy.⁶
• Measurement is being standardized. Work on LC-MS/MS assays and harmonized reference ranges has improved accuracy at low concentrations and clarified the value of calculated free testosterone, reducing the misclassification that plagued older immunoassays.¹³
• In women, indications are narrow. The international Global Consensus Position Statement restricts testosterone therapy in women to hypoactive sexual desire disorder after menopause and stresses that there is no reliable blood test for female testosterone "deficiency."⁸

These findings concern diagnosis and management; they do not authorize any self-treatment and do not replace your physician's advice.

Get your testosterone interpreted by AI DiagMe

A testosterone result is never read alone: its meaning depends on the time of the draw, your SHBG and free testosterone, your weight, your symptoms, and the rest of the hormone panel. That cross-reading is what gives the number its true value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole context into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

Bottom line

The testosterone blood test measures the main androgen in three forms — total, free, and bioavailable — with SHBG shaping how much is active, and it must be drawn in the morning to be meaningful. In men, remember the order of magnitude (~ 300 – 1,000 ng/dL), that low testosterone (hypogonadism) takes two low morning samples plus symptoms to diagnose, and that obesity is a common, reversible cause. In women, a high result usually points toward PCOS. No value is read alone: it's the combination with LH, FSH, prolactin, SHBG, and your symptoms — the whole hormone panel and your profile — that makes sense of it, exactly what AI DiagMe does, alongside your physician.

Sources

Official U.S. sources and peer-reviewed publications (PubMed) used for this guide: