A total testosterone level below 300 nanograms per deciliter (ng/dL) is generally considered low. Both the American Urological Association and the Endocrine Society use this threshold, and it’s the cutoff most doctors rely on when evaluating whether symptoms might be tied to a testosterone deficiency. But the number alone doesn’t tell the whole story.
The 300 ng/dL Threshold
Normal testosterone in adult men falls between 300 and 1,000 ng/dL, with the AUA describing healthy levels as roughly 450 to 600 ng/dL. The Endocrine Society’s lower limit, calibrated against healthy, non-obese young men, lands at 264 ng/dL. In practice, most clinicians treat 300 ng/dL as the working cutoff for low testosterone.
That said, a single blood draw below 300 doesn’t automatically mean you have a deficiency. Guidelines require at least two separate blood tests, both drawn in the early morning (typically between 8 and 10 a.m.), because testosterone peaks during those hours and drops throughout the day. A test taken at 3 p.m. could read significantly lower than one taken at 8 a.m. in the same person. Your provider may also ask you to fast beforehand.
Why a Number Isn’t Enough for a Diagnosis
Low testosterone, clinically called hypogonadism, is only diagnosed when low blood levels show up alongside actual symptoms. A man with a reading of 280 ng/dL who feels fine and has no complaints would not typically receive a diagnosis or treatment. The combination of lab results and symptoms is what matters.
The symptoms doctors look for fall into three categories:
- Sexual: reduced sex drive and weaker erections
- Physical: fatigue, reduced energy, loss of muscle mass, loss of body or facial hair, decreased endurance, and weight gain
- Cognitive and emotional: depressive symptoms, poor concentration, memory problems, irritability, and reduced motivation
Many of these overlap with other conditions like depression, sleep apnea, or thyroid problems, which is one reason doctors don’t rely on symptoms alone.
Total vs. Free Testosterone
Most of the testosterone in your blood is bound to a protein called sex hormone-binding globulin (SHBG). Only a small fraction circulates “free,” meaning it’s available for your body to actually use. A standard blood test measures total testosterone, which includes both the bound and free forms, but can’t distinguish between them.
This creates a potential blind spot. If your SHBG levels are unusually high, a large share of your testosterone is locked up and unavailable to your tissues, even if your total number looks normal. You could have symptoms of low testosterone with a total reading of 400 ng/dL. The reverse is also true: low SHBG means more of your testosterone is free and active, so a total reading that looks borderline might actually be adequate. When total testosterone comes back in the gray zone or doesn’t match a patient’s symptoms, doctors will often order a free testosterone test or an SHBG test to get a clearer picture.
How Testosterone Changes With Age
Testosterone levels tend to decline by about 1 to 2 percent per year after age 30. This is a gradual process, and most men stay within the normal range well into older age. But the slow decline means that a man in his 60s or 70s is more likely to dip below 300 ng/dL than a man in his 30s. The reference range of 264 to 916 ng/dL used by major labs applies broadly to men 18 and older, without age-specific cutoffs, which is why the same 300 ng/dL threshold is used regardless of age.
Conditions That Increase the Risk
Obesity and type 2 diabetes are two of the strongest predictors of low testosterone. Among obese men without diabetes who are 45 or older, roughly 40 percent have below-normal free testosterone levels. In obese men with diabetes, that number climbs to about 50 percent. Even being overweight without obesity raises the prevalence to around 29 percent in non-diabetic men. Excess body fat increases the conversion of testosterone to estrogen and tends to raise SHBG in unpredictable ways, both of which push functional testosterone levels down.
Other conditions linked to low testosterone include chronic opioid use, obstructive sleep apnea, kidney disease, and certain pituitary disorders. Testicular injuries or infections can also reduce testosterone production directly.
Primary vs. Secondary Causes
When testosterone is confirmed low, doctors sometimes investigate where the problem originates. The distinction matters because it points to different underlying causes.
In primary hypogonadism, the testes themselves aren’t producing enough testosterone. The brain responds by ramping up its signaling hormones (called LH and FSH) to try to stimulate production, so blood tests show low testosterone alongside elevated LH and FSH. Causes include testicular injury, genetic conditions, and certain infections.
In secondary hypogonadism, the problem starts in the brain. The pituitary gland or hypothalamus isn’t sending adequate signals to the testes, so LH and FSH are low or inappropriately normal despite low testosterone. This form is more commonly linked to obesity, pituitary tumors, or the use of certain medications including opioids and anabolic steroids.
When Treatment Is Considered
Testosterone replacement therapy requires both confirmed low levels (below 300 ng/dL on two separate morning tests) and symptoms significant enough to affect quality of life. A borderline number without symptoms, or symptoms without a confirmed low reading, typically won’t lead to a prescription.
Before starting treatment, doctors also rule out reversible causes. Losing weight, improving sleep, and stopping medications that suppress testosterone can sometimes bring levels back into the normal range without hormone therapy. For men with obesity-related low testosterone, even modest weight loss can produce a measurable increase.
For those who do start treatment, the goal is to bring testosterone into the mid-normal range and relieve symptoms. Common improvements include better energy, improved mood, increased sex drive, and gradual gains in muscle mass. Results vary, and not every symptom responds equally.