Total Testosterone Test · Blood

Your testosterone level is one of the most revealing numbers in men's health. It shapes your energy, your body composition, your mood, your sex drive, and your risk of chronic disease. Yet most men have no idea what theirs is until something goes wrong. By the time symptoms like fatigue, weight gain, or low libido become obvious, levels may have been sliding for years.

Total testosterone (the full name for the primary male sex hormone) measures all the testosterone circulating in your blood, including the portion bound to carrier proteins and the small fraction floating free. In men, over 95% comes from the testes, with a small contribution from the adrenal glands. Women produce much smaller amounts from the ovaries and adrenals. This single number reflects how well the entire signaling chain from brain to testes is functioning.

How Testosterone Works in Your Body

Testosterone production follows a chain of command. Your brain's hypothalamus sends a signal (GnRH) to the pituitary gland, which responds by releasing luteinizing hormone (LH). LH travels through the blood to specialized cells in the testes called Leydig cells, which manufacture testosterone from cholesterol. Healthy men produce roughly 4 to 9 milligrams per day, resulting in blood levels between 290 and 1,010 ng/dL.

Once released, most testosterone rides through the bloodstream attached to proteins. About half binds tightly to sex hormone-binding globulin (SHBG), another large portion binds loosely to albumin, and only about 2 to 4% circulates free. That free fraction is the most biologically active, which is why total testosterone sometimes tells an incomplete story when the carrier proteins themselves are abnormally high or low.

Testosterone also serves as a raw material for other hormones. An enzyme called 5-alpha-reductase converts it into dihydrotestosterone (DHT), a more potent androgen responsible for effects like body hair growth and prostate function. Another enzyme, aromatase, converts testosterone into estradiol, a form of estrogen. This dual role means testosterone sits at a metabolic crossroads, influencing everything from bone density to cardiovascular health.

Why Low Testosterone Matters

Low testosterone in men, sometimes called hypogonadism, can result from a problem at any point in the signaling chain. When the testes themselves fail (from injury, genetic conditions like Klinefelter syndrome, or chemotherapy), it is called primary hypogonadism, and LH levels rise as the brain tries harder to stimulate production. When the brain or pituitary is the source of the problem (from tumors, chronic opioid use, or high prolactin), it is called secondary hypogonadism, and LH stays low or normal.

A third category, functional hypogonadism, is the most common and the most relevant to people managing their health proactively. Obesity, type 2 diabetes, sleep apnea, chronic illness, and severe calorie restriction can all suppress the brain-to-testes signaling chain without any structural damage. In these cases, the low testosterone is a consequence of the underlying condition, and addressing that condition often restores levels.

Symptoms of low testosterone include reduced sex drive, erectile dysfunction, low energy, loss of muscle mass, depressed mood, and reduced bone density. The diagnosis requires both a confirmed low level on blood testing and the presence of symptoms; a low number alone does not automatically mean treatment is needed.

Mortality Risk

A large individual participant data meta-analysis pooling over 255,000 participant-years of follow-up found that all-cause mortality risk increased when testosterone fell below about 7.4 nmol/L (213 ng/dL), with cardiovascular death risk rising below 5.3 nmol/L (153 ng/dL). These thresholds held after adjusting for age, BMI, smoking, and other risk factors.

UK Biobank data from nearly 150,000 men followed for 11 years found that men in the lowest fifth of testosterone were about 14% more likely to die from any cause and 20% more likely to die from cancer compared to men in the highest fifth. A separate meta-analysis of over 359,000 participants found a U-shaped pattern: both very low and very high levels were associated with increased mortality.

Sources: Yeap et al. (2024) Annals of Internal Medicine; Yeap et al. (2021) JCEM; Raeisi-Dehkordi et al. (2025) JCEM.

What this means for you: these findings do not prove that low testosterone directly causes death. It may act as a barometer of general health, declining alongside other risk factors like obesity, diabetes, and inactivity. But the consistency of the signal across large populations makes a strong case for knowing your level and watching its trajectory.

Heart Disease

The relationship between testosterone and cardiovascular disease is more nuanced than early headlines suggested. A UK Biobank analysis of over 210,000 men tracked for 9 years found that lower total testosterone was not significantly associated with increased heart attacks or major cardiovascular events after adjusting for lifestyle and medical factors. The hazard ratio for the lowest versus highest quintile was 0.89 for heart attack and 0.92 for major cardiovascular events, neither reaching statistical significance.

This finding is striking because it contrasts with the mortality data. One interpretation is that testosterone is a marker of metabolic health rather than a direct cardiovascular driver. Men with low testosterone tend to carry more body fat, have higher blood sugar, and carry more metabolic risk factors. Once those factors are accounted for, the independent heart risk from low testosterone diminishes.

Type 2 Diabetes

The link between testosterone and diabetes risk is one of the strongest and most actionable associations in men's health. A meta-analysis of prospective studies found that men with higher testosterone levels were about 42% less likely to develop type 2 diabetes. A more recent meta-analysis of 22 studies with over 43,000 men confirmed the direction: low testosterone was associated with about 52% higher odds of developing diabetes.

The relationship runs in both directions. Low testosterone promotes insulin resistance and fat accumulation, while obesity and insulin resistance suppress testosterone production. This bidirectional loop means that catching a downward trend early gives you a window to intervene before either condition entrenches itself.

Cancer

UK Biobank data from over 182,000 men found that higher free testosterone (the unbound fraction, not total testosterone) was associated with increased risk of prostate cancer (about 10% higher risk per 50 pmol/L increase) and melanoma (about 35% higher risk per 50 pmol/L increase). Men in the lowest quintile of total testosterone also showed about 20% higher cancer mortality in total, creating a paradox: very low levels are linked to higher cancer death, while higher free testosterone is linked to certain specific cancer types.

This complexity means you should not interpret a high testosterone level as inherently dangerous for cancer. The mortality data suggests that maintaining healthy levels is protective on the whole, while the cancer-specific data reinforces the value of prostate screening in men with high levels.

Bone Health

Testosterone plays a direct role in maintaining bone mineral density. The Endocrine Society notes that skeletal health may be compromised when testosterone falls below roughly 200 to 250 ng/dL. Men with baseline testosterone below 200 ng/dL who received testosterone therapy showed the greatest improvements in hip bone density in clinical trials. For men focused on long-term health, a testosterone level well above this threshold offers some reassurance about bone strength.

Reference Ranges

Reference ranges for testosterone vary depending on the lab, the assay used, and whether the sample meets quality standards. The most reliable reference range comes from the CDC Harmonized Reference Range, derived from a study of 9,054 men across four cohorts in the U.S. and Europe, with percentile values based on healthy, non-obese men aged 19 to 39 using gold-standard testing.

These tiers are drawn from published research using CDC-certified assays. Your lab may use different methods and cutpoints. Compare your results within the same lab over time for the most meaningful trend.

When 1,133 laboratories using 14 different assays measured testosterone in the same quality-control blood sample, the reported value ranged from 45 to 365 ng/dL. This enormous spread means a single result near any cutpoint is unreliable without confirmation. Always repeat a borderline or low result at the same lab before drawing conclusions.

Age-specific data from NHANES shows that the lower end of normal for men in their 20s is higher than the traditional 300 ng/dL cutoff, ranging from about 409 ng/dL at ages 20 to 24 down to about 350 ng/dL by ages 40 to 44. If you are in your 20s or 30s and your level is 320 ng/dL, that may be lower than expected for your age group even though it falls within the standard lab range.

Women's Ranges

Women produce far less testosterone, with normal levels between roughly 10 and 57 ng/dL (0.35 to 1.97 nmol/L). Levels above about 144 ng/dL (5 nmol/L) warrant investigation for conditions like polycystic ovary syndrome (PCOS), ovarian tumors, or adrenal disorders. Testosterone in women also varies across the menstrual cycle, with higher levels during the mid-luteal phase.

Tracking Your Trend

A single testosterone reading is a snapshot taken through a foggy window. Day-to-day biological variation for morning samples runs about 18.7%, and the reference change value (the minimum difference needed to confirm a real change between two results) is 52%. That means if your level is 400 ng/dL, normal fluctuation alone could produce readings anywhere from roughly 285 to 515 ng/dL without anything meaningful changing in your body.

This is why 30% of men with an initially low testosterone have normal levels on repeat testing. One low result does not mean you are deficient. One normal result does not mean everything is fine. The trajectory matters far more than any single point.

Get a baseline reading as early as your late 20s or early 30s. If you are making lifestyle changes (losing weight, starting a new exercise program, adjusting your diet), retest in 3 to 6 months to see whether those changes are moving the number. After that, check at least annually. Testosterone declines roughly 0.4 to 1.6% per year after the mid-30s, so a gradual downward trend is expected. What you want to catch is a steep drop or a level that falls below age-appropriate norms well before you develop symptoms.

When Results Can Be Misleading

Testosterone has a strong circadian rhythm, peaking between 7 and 10 AM and dipping to levels that can fall below the normal range by evening, even in healthy men. This rhythm flattens somewhat after age 60 but does not disappear. Always draw blood in the early morning.

Eating before your blood draw can lower your result by 15 to 17% on average, with the dip peaking about an hour after the meal. One study found that 11 to 56% of men with genuinely normal testosterone levels dipped below 300 ng/dL after eating. Always fast before testing.

Acute illness or surgery can slash testosterone by 43 to 58% within 24 hours, sometimes dropping levels into the castrate range. This suppression can last days to weeks. Wait at least 2 to 4 weeks after recovery from any significant illness before testing.

Intense exercise produces a transient testosterone spike immediately afterward, which returns to baseline within 30 to 60 minutes. However, very prolonged or intense training can suppress levels for up to 72 hours during recovery. Avoid testing within a day or two of an unusually hard training session.

Several common medications shift the number without necessarily indicating a testosterone disorder. Corticosteroids like prednisone (at doses of 15 mg or more daily) can suppress testosterone by 33 to 55% within days. Opioids are even more potent suppressors, occasionally driving levels into the castrate range. Metformin lowers testosterone modestly in men with type 2 diabetes, though this effect is typically small. If you are on any of these medications, your result may reflect drug effects rather than your underlying hormonal health. Let your provider know what you are taking before interpreting results.

When Total Testosterone Can Mislead

Total testosterone includes both bound and free fractions. When SHBG (the main carrier protein) is abnormally high or low, total testosterone can paint a misleading picture. Obese men and those with diabetes tend to have low SHBG, which drags total testosterone down even though their free (active) testosterone may be perfectly normal. These men often do not have symptoms of deficiency. Older men, those with liver disease, and those taking certain medications tend to have high SHBG, which can push total testosterone into the normal range even when free testosterone is genuinely low.

Data from a large European study found that men with low free testosterone had sexual and physical symptoms regardless of their total testosterone reading, while men with low total but normal free testosterone (typically obese men with low SHBG) did not. If your total testosterone is borderline (roughly 200 to 400 ng/dL) or you have a condition known to alter SHBG, measuring free testosterone and SHBG alongside total testosterone gives a much clearer picture.