The most reliable way to check your testosterone levels is a simple blood test, drawn from a vein in your arm between 7 a.m. and 10 a.m., when your levels are at their daily peak. Labs set their normal reference ranges based on samples collected during this morning window, so testing later in the day can give you an artificially low reading. Here’s what you need to know before, during, and after the test.
Why Timing Matters
Testosterone follows a daily rhythm. It peaks in the early morning and drops throughout the day, sometimes by a significant margin. If you get your blood drawn at 2 p.m. instead of 8 a.m., your result could come back lower than your actual baseline. Because labs calibrate their “normal” ranges using morning samples, a midday draw can make a normal level look borderline or low.
For adult men, the normal range for total testosterone is roughly 193 to 824 ng/dL. For adult women, it’s under 40 ng/dL. These ranges shift during puberty and adolescence, but for most adults checking their levels, the 193 to 824 window is what your result will be compared against.
Total vs. Free Testosterone
Most of the testosterone circulating in your blood is bound to proteins, primarily one called sex hormone-binding globulin (SHBG) and another called albumin. When testosterone is bound to these proteins, your body can’t easily use it. That’s actually by design: keeping most testosterone locked up prevents your body from burning through it too quickly.
The small fraction that isn’t attached to any protein is called free testosterone, and it’s the portion that’s immediately available to build muscle, maintain bone density, and support other functions. A standard blood test measures total testosterone, which includes both the bound and free forms. This is the most common test and usually the first one ordered. A free testosterone test is less routine but can be useful if your total testosterone looks normal yet you still have symptoms, since it’s possible for SHBG levels to be unusually high, leaving less testosterone available for your body to actually use.
Signs That Warrant Testing
Not every symptom people attribute to low testosterone actually points there. The most specific indicators are sexual: noticeably low sex drive, loss of morning or spontaneous erections, and difficulty getting or keeping an erection. These symptoms correlate most reliably with low testosterone levels.
Other signs that strongly suggest a hormonal issue include loss of armpit and pubic hair, shrinking testicles, hot flashes, and a very low sperm count. Less specific but still relevant symptoms include depressed mood, trouble concentrating, increased body fat, loss of muscle mass and endurance, and enlarged breast tissue in men. Any of these on their own could have a dozen causes, but a cluster of them, especially the sexual symptoms, is a good reason to get tested.
How to Prepare for the Test
Schedule your blood draw for early morning. Your provider may ask you to fast for several hours beforehand, so check with them when booking. Fasting isn’t always required, but it can affect certain hormone measurements, and the Endocrine Society specifically recommends fasting morning samples for diagnosing low testosterone.
If you take biotin supplements, be aware that biotin can interfere with hormone blood tests. Many supplements marketed for hair, skin, and nails contain biotin at doses hundreds of times higher than the 30 micrograms considered adequate for adults. The FDA has flagged this as a real problem that can skew results. Let your provider know if you’re taking biotin so they can advise you on when to stop before your draw.
What Happens at the Lab
The test itself is a standard blood draw from a vein, usually in your arm. It takes a few minutes. Results typically come back within a day or two, depending on the lab. Your report will show your total testosterone level in ng/dL alongside the lab’s reference range.
One low result isn’t enough for a diagnosis. The Endocrine Society guidelines require at least two separate morning blood draws showing consistently low levels, combined with symptoms, before diagnosing testosterone deficiency. Testosterone fluctuates day to day based on sleep, stress, illness, and other factors, so a single snapshot can be misleading.
Additional Tests Your Doctor May Order
If your testosterone comes back low, your provider will likely want to understand why. Two hormones produced by the pituitary gland, called LH and FSH, help pinpoint the source of the problem. These hormones act as signals telling the testicles (or ovaries) to produce testosterone and sperm.
If LH and FSH are high, it usually means the pituitary is working overtime trying to stimulate the reproductive glands, but those glands aren’t responding properly. This points to a problem in the testicles themselves. If LH and FSH are low, the issue is more likely in the brain, either the pituitary gland or the hypothalamus, which aren’t sending the right signals. This distinction matters because the underlying cause determines the treatment approach.
Are Home Test Kits Reliable?
Home testosterone kits, typically using a finger-prick blood spot, are widely available online. Their convenience is appealing, but their accuracy is a real concern. In one study comparing six different home testing kits, results varied between 26% and 41% in men and up to 115% in women. When those home kit results were compared against an established clinical method, the average deviation was 194% in men. That’s not a rounding error; it’s a result that could show you as critically low when you’re normal, or normal when you’re actually low.
Clinical labs, by contrast, generally stay within 20% of gold-standard methods, and certified labs must report testosterone values within 6.4% of reference samples. If you’re testing out of curiosity and want a rough sense of where you stand, a home kit can serve as a conversation starter. But if you’re experiencing symptoms or trying to make decisions about treatment, a clinical blood draw is the only result worth trusting.
Reading Your Results
For adult men (18 and older), total testosterone between 193 and 824 ng/dL falls within the normal range. For adult women, under 40 ng/dL is considered normal. Keep in mind that “normal” is a wide band. A 25-year-old at 300 ng/dL is technically in range but sits near the bottom, while an identical number in a 70-year-old is right where you’d expect it. Context matters: your symptoms, your age, and how you feel day to day all factor into whether a number on paper actually represents a problem.
If your result falls below 193 ng/dL on two separate morning fasting draws and you have symptoms, that meets the Endocrine Society’s criteria for testosterone deficiency. From there, the next step is identifying the cause through additional bloodwork, which your provider will guide based on your specific situation.