The only reliable way to know your testosterone level is through a blood test, typically ordered by a doctor or purchased through a direct-to-consumer lab. The standard test measures total testosterone, and results below 300 ng/dL are generally considered low by major medical guidelines. But getting an accurate number involves more than just showing up for a blood draw. Timing, test type, and even what your body does with testosterone all affect what the results actually mean.
What a Testosterone Blood Test Measures
Most of the testosterone in your blood is bound to proteins, mainly one called sex hormone-binding globulin (SHBG). Only a small fraction floats freely. The three types of testosterone tests reflect this:
- Total testosterone measures both bound and free testosterone combined. This is the standard first test and the one most labs run by default.
- Free testosterone measures only the unattached portion. It’s less commonly ordered but can be useful when total testosterone looks normal yet symptoms persist.
- Bioavailable testosterone measures free testosterone plus the portion loosely bound to a second protein (albumin), which the body can still use. This test is rarely ordered on its own.
For most people, total testosterone is enough to get a clear picture. Free testosterone becomes important in specific situations, particularly when SHBG levels are unusually high or low. Conditions like obesity, liver disease, thyroid disorders, and estrogen use can all shift SHBG levels, which in turn makes total testosterone a less reliable indicator of what your body actually has available. SHBG also tends to rise with age, meaning your free testosterone can drop even when your total number looks fine.
When and How to Get Tested
Testosterone follows a daily cycle. Levels peak in the early morning, between about 7:00 and 10:00 a.m., then drop to their lowest point in the evening before rising again overnight. Current clinical recommendations call for a blood draw between 8:00 and 9:00 a.m. to capture your peak and minimize the effect of this natural fluctuation. A test taken at 3:00 p.m. could read significantly lower than one taken at 8:00 a.m., not because anything is wrong, but because of normal biology.
You have a few options for getting the test done. Your primary care doctor or a specialist can order standard lab work. You can also use direct-to-consumer lab services that let you order a blood test online and visit a local lab for the draw. At-home kits that use saliva or a finger-prick blood spot are the most convenient option, but they come with tradeoffs. Blood testing is more precise and can measure both total and bound hormone levels, while saliva tests may not detect subtle changes and are more vulnerable to contamination or timing errors. If you’re looking for a number you can trust and potentially act on, a standard blood draw at a lab is the better choice.
Why One Test Isn’t Enough
Testosterone levels fluctuate from day to day. Stress, poor sleep, illness, and even a heavy meal can temporarily push your number up or down. Because of this variability, a single low reading doesn’t confirm a problem. The American Urological Association recommends confirming a low result with at least one additional morning blood test on a separate day before considering a diagnosis of testosterone deficiency. Two consistent readings below 300 ng/dL, combined with symptoms, form the basis for that diagnosis.
How Lab Accuracy Varies
Not all labs process testosterone samples the same way. The most accurate method, sometimes called mass spectrometry, provides consistently high precision across the full range of clinically relevant concentrations. The CDC has validated this approach, showing it maintains accuracy within about 4 to 5 percent across low, mid, and high testosterone levels. Many standard labs use a faster, cheaper method called an immunoassay, which is reasonably accurate for men with levels in the normal range but can be less reliable at very low or very high concentrations. If your results come back borderline or unexpected, it’s worth asking which method your lab used.
Signs That Suggest Testing Is Worthwhile
Some men with low testosterone have no noticeable symptoms at all. Others experience a combination of physical, sexual, and cognitive changes that can develop so gradually they’re easy to dismiss. Common signs include low sex drive, difficulty getting or maintaining erections, decreased muscle size and strength, increased body fat (especially around the midsection), bone loss, sleep problems like insomnia, trouble concentrating, and depression. None of these symptoms are unique to low testosterone, which is exactly why a blood test is the only way to confirm whether testosterone is actually the issue.
Making Sense of Your Results
The American Urological Association uses 300 ng/dL as the clinical cutoff for low testosterone in men. But “normal” ranges on lab reports typically span from roughly 300 to 1,000 ng/dL, and where you fall within that range matters less than how you feel and whether your level is consistent over time. A man at 320 ng/dL with significant symptoms may benefit from further evaluation, while another at 350 ng/dL with no complaints may not need any intervention.
If your total testosterone comes back in the low-normal range but you’re still experiencing symptoms, your doctor may check free testosterone or SHBG levels to see whether enough testosterone is actually reaching your tissues. This is especially relevant if you’re over 50, carry significant extra weight, or have a condition that affects the liver or thyroid. SHBG levels rise with age, and higher SHBG means more testosterone gets locked up and unavailable, even when the total number looks adequate on paper.
Context also matters for women, who produce testosterone in smaller amounts. Normal ranges for women are much lower, typically between 15 and 70 ng/dL, and testing may be done to investigate symptoms like irregular periods, excess hair growth, or fertility issues. The same principles apply: morning blood draw, repeat testing to confirm, and attention to SHBG when results are ambiguous.
How to Prepare for the Test
Schedule your blood draw for early morning, ideally between 8:00 and 9:00 a.m. Get a normal night’s sleep beforehand, since sleep deprivation can temporarily lower testosterone. If you take biotin supplements (common in hair and nail vitamins), mention this to your provider, as high-dose biotin can interfere with some hormone assays. Let your doctor know about any medications you’re taking, particularly opioids, steroids, or hormone-related treatments, since these can directly affect your results. Some labs recommend fasting, though this isn’t universally required for testosterone specifically. Check with your lab ahead of time.