Testosterone is tested with a simple blood draw, typically from a vein in your arm, done in the early morning when levels are at their highest. The most common version is a total testosterone test, which measures all the testosterone in your blood at once. If results come back low, a second test on a separate morning is required before a diagnosis can be made.
Types of Testosterone Tests
There are three versions of the test, and they each measure something slightly different. A total testosterone test is the standard starting point. It captures all the testosterone circulating in your blood, both the portion that floats freely and the portion bound to proteins. Most of the time, this single number is enough to determine whether your levels fall within a normal range.
A free testosterone test measures only the small fraction of testosterone (roughly 2 to 3%) that isn’t attached to any protein. This unbound testosterone is what your body can actually use for things like muscle growth, bone density, and sex drive. Your doctor may order this test if your total testosterone looks normal but you still have symptoms, or if conditions like obesity, diabetes, or aging might be skewing the total number.
A bioavailable testosterone test is the least common. It measures free testosterone plus testosterone loosely bound to a protein called albumin, which can still be released for your body to use. It’s occasionally helpful when standard results don’t match a patient’s symptoms.
Why Total Testosterone Can Be Misleading
About half of the testosterone in your blood is tightly bound to a protein called SHBG (sex hormone-binding globulin). Once testosterone latches onto SHBG, it’s essentially locked up and can’t interact with your tissues. The total testosterone test can’t distinguish between this locked-up testosterone and the free testosterone your body actually uses. So you could have a normal total number but still not have enough usable testosterone, or vice versa.
Several things shift SHBG levels. Aging, liver disease, and hyperthyroidism tend to raise SHBG, which traps more testosterone and can leave you with low-T symptoms despite a “normal” total reading. Obesity, insulin resistance, and hypothyroidism tend to lower SHBG, freeing up more testosterone. When your doctor suspects SHBG is distorting the picture, they’ll order an SHBG blood test alongside total testosterone to estimate how much of your testosterone is actually available.
How to Prepare for the Test
Testosterone follows a daily rhythm, peaking in the early morning and declining throughout the day. For men under 45, this swing is substantial. One study found that men under 40 had total testosterone readings about 207 ng/dL lower in samples drawn after 9 AM compared to samples drawn between 7 and 9 AM. That’s a large enough difference to push a normal result into the “low” range, or the reverse. For this reason, guidelines recommend drawing blood before 9 AM.
The daily fluctuation becomes less dramatic with age. Men over 45 show a smaller morning-to-afternoon drop, but early-morning testing is still considered the standard across all age groups. Your provider may also ask you to fast for several hours beforehand, since food intake and blood sugar changes can influence results.
What Happens During the Blood Draw
The test itself is a standard venous blood draw. A technician wraps a band around your upper arm, inserts a needle into a vein (usually at the inside of your elbow), and collects a small tube of blood. The whole process takes a few minutes. There’s no special recovery. Results typically come back within a few days, depending on the lab.
How Labs Analyze the Sample
Not all lab methods are equally accurate, and this matters more than most people realize. The two main technologies are immunoassay and mass spectrometry (LC-MS/MS).
Immunoassay is the older, more widely available method. It works well for testosterone levels in the typical male range but becomes unreliable at low concentrations, below about 100 ng/dL. One study comparing the two methods found that immunoassay readings were 20% lower than mass spectrometry readings on average, with minimal correlation between the two at low concentrations. That’s a significant gap when the difference between “low” and “normal” determines whether someone starts treatment.
Mass spectrometry is more precise across the full range of testosterone levels, from very low to very high. It’s considered the gold standard and is increasingly preferred by endocrinologists. A validated mass spectrometry assay can achieve accuracy within about 6% of the true value across concentrations from 2.5 to 1,000 ng/dL. If your results are borderline or unexpectedly low, it’s worth asking whether the lab used mass spectrometry, particularly if you’re a woman or a man whose levels are expected to be on the lower end.
What the Numbers Mean
The American Urological Association uses 300 ng/dL as the cutoff for low testosterone in men. Below that threshold, combined with symptoms like fatigue, low libido, reduced muscle mass, or mood changes, a diagnosis of testosterone deficiency may be considered. The number alone isn’t enough. A level of 280 ng/dL without symptoms doesn’t automatically mean treatment, and a level of 310 ng/dL with clear symptoms may still warrant further investigation with free testosterone or SHBG testing.
Normal ranges vary slightly between labs, and what counts as “normal” also depends on age. Most reference ranges for adult men fall somewhere between 270 and 1,070 ng/dL, though younger men typically sit higher in that range.
Why Two Tests Are Required
A single low result isn’t considered diagnostic. Testosterone levels fluctuate day to day based on sleep, stress, illness, alcohol intake, and dozens of other variables. Up to 30% of men who test low on their first draw will have a normal result on a repeat test two to three weeks later. Because of this, guidelines require two separate early-morning blood draws showing low levels before a formal diagnosis is made.
Are Home and Saliva Tests Reliable?
Home testing kits, especially saliva-based ones, are appealing because they skip the blood draw entirely. But their accuracy doesn’t hold up well against standard blood tests. Research comparing saliva testosterone levels to serum (blood) measurements found only a weak correlation between the two, with correlation coefficients between 0.17 and 0.26, essentially near-random. Even after statistical adjustments, the correlation only reached a modest 0.44. The gold standard for measuring biologically active testosterone remains a blood test.
Finger-prick blood spot tests, offered by some at-home kits, are more reliable than saliva but still less precise than a full venous draw. They can be a reasonable screening tool if getting to a lab is difficult, but any abnormal result should be confirmed with a standard blood draw before making treatment decisions.