Testosterone is tested with a simple blood draw, typically from a vein in your arm, and the most common version is a total testosterone test. But getting an accurate result depends heavily on when you test, whether you’ve eaten, and which type of test your provider orders. Here’s what you need to know to get a reliable reading.
Total, Free, and Bioavailable Tests
There are three types of testosterone measurements, and they each tell a different story. A total testosterone test measures all the testosterone in your blood, both the portion floating freely and the portion bound to proteins. This is the standard first test most providers order.
A free testosterone test measures only the small fraction of testosterone that isn’t attached to any protein. This unbound testosterone is what your body can actually use in tissues and muscles. A bioavailable testosterone test captures free testosterone plus testosterone loosely attached to a protein called albumin, which can also become active in your tissues. It excludes testosterone tightly bound to a carrier protein called SHBG (sex hormone-binding globulin), which locks testosterone away so your body can’t easily use it.
For most people, total testosterone is the starting point. But total testosterone alone can be misleading. You could have a normal total level while most of it is locked up by SHBG, leaving too little free testosterone available. This is why providers often order an SHBG test alongside total testosterone to estimate how much is actually active. If your SHBG is high, your tissues may not be getting enough testosterone even though the total number looks fine. If SHBG is low, more testosterone is free and available than the total number suggests.
When and How to Get Tested
Testosterone follows a predictable daily rhythm. Levels peak between 7:00 and 10:00 a.m., drop to their lowest point in the evening, then begin climbing again overnight. In men aged 30 to 40, morning levels run 30 to 35% higher than levels measured in the mid to late afternoon. That’s a massive swing from the same person on the same day.
To minimize this variability, current guidelines recommend drawing blood between 8:00 and 9:00 a.m. Testing later in the day can produce artificially low results that don’t reflect your true baseline. Food intake also suppresses testosterone temporarily, so fasting before your morning draw gives the most accurate reading. Leading clinical recommendations call for an early morning, fasting blood draw, and repeating it on a separate day to confirm the result before any diagnosis is made.
What the Numbers Mean
The American Urological Association uses 300 ng/dL as the cut-off for low testosterone in men. A total testosterone level below that threshold, confirmed on at least two separate morning tests, supports a diagnosis of testosterone deficiency. Labs may list slightly different reference ranges, but 300 ng/dL is the widely accepted clinical benchmark.
For women, normal total testosterone ranges are much lower and decline gradually with age. A woman in her 20s typically falls between about 5 and 21 ng/dL, while a woman in her 60s ranges from roughly 3.7 to 14 ng/dL. By the 80s, the range narrows to approximately 2.9 to 10.5 ng/dL. These numbers matter because testosterone plays a role in energy, bone density, and libido in women too, though it’s tested less routinely.
Keep in mind that reference ranges vary between labs because different testing methods produce slightly different results. Always compare your number to the specific range printed on your lab report rather than to a generic chart online.
At-Home Saliva and Finger-Prick Kits
Mail-order testosterone kits have become popular, and most use either a saliva sample or a finger-prick blood spot. They’re convenient, but accuracy varies. Saliva tests measure a form of testosterone that doesn’t directly correspond to the free testosterone measured in blood. Testosterone binds to proteins in saliva itself, which inflates the reading, particularly in women where it can produce values more than double the expected free testosterone level.
Collection method also matters. Passive drooling into a tube produces a much stronger correlation with lab-grade blood results than using an absorbent swab (like a Salivette). Even with the better collection method, the correlation with gold-standard blood testing is moderate, not strong. Saliva kits can give you a rough directional signal, but they aren’t precise enough to diagnose a deficiency or guide treatment decisions. A standard venous blood draw at a lab remains the most reliable option.
Supplements and Medications That Skew Results
Biotin is the most common supplement that interferes with testosterone testing. Many people take it for hair, skin, or nail health, and it’s included in numerous multivitamins. At doses of 5 mg per day or higher, biotin can cause the immunoassay machines labs use to produce falsely elevated testosterone readings. The interference isn’t biological; it’s an artifact of how the test chemistry works.
If you take biotin supplements, stop them at least one to three days before your blood draw. Higher doses or impaired kidney function can extend the time needed to clear biotin from your system, so a longer washout period is safer if you’ve been taking large amounts. This is easy to overlook because biotin is in so many over-the-counter products, and most people don’t realize it can affect lab work.
Getting the Most Accurate Result
A few straightforward steps make a real difference in the reliability of your results:
- Test early. Schedule your blood draw between 7:00 and 10:00 a.m., ideally around 8:00 to 9:00.
- Fast overnight. Avoid eating or drinking anything besides water after midnight the night before.
- Pause biotin. Stop biotin-containing supplements at least two days before testing.
- Repeat the test. A single low result isn’t enough for a diagnosis. Confirm it with a second fasting morning draw on a different day.
- Request SHBG if symptoms persist. If your total testosterone is in the normal range but you still have symptoms like fatigue, low libido, or mood changes, an SHBG test can reveal whether enough testosterone is actually available to your body.
Testosterone levels naturally fluctuate from day to day and even hour to hour. Controlling for as many variables as possible, especially timing and fasting, gives you the clearest picture of where you actually stand.