The only reliable way to know your testosterone level is a blood test, specifically a venous blood draw taken in the early morning. Symptoms like low energy, reduced sex drive, or changes in body composition can suggest your levels are off, but dozens of other conditions cause the same problems. A number on a lab report is what gives you a real answer.
That said, understanding the signs, knowing what the test actually measures, and getting the timing right all matter if you want results you can trust.
Signs That May Point to Low Testosterone
Testosterone affects far more than sex drive. In men, low levels can show up as a combination of physical and mental changes: reduced muscle size and strength, increased body fat (especially around the midsection), difficulty getting or maintaining erections, low sperm count, and bone loss over time. Sleep problems, trouble concentrating, and depression are also common. Some men with low testosterone have no obvious symptoms at all, which is one reason blood testing matters.
In women, testosterone plays a quieter but still important role. Low levels can cause persistent fatigue, loss of muscle tone, thinning hair, vaginal dryness, irregular periods, and difficulty conceiving. Depression, anxiety, and low libido are frequently reported as well. Because these symptoms overlap heavily with thyroid disorders, iron deficiency, perimenopause, and other conditions, self-diagnosis based on symptoms alone is unreliable for either sex.
What a Testosterone Blood Test Measures
Most of the testosterone in your blood is bound to proteins, which means your body can’t readily use it. A smaller fraction floats freely and is available for building muscle, maintaining bone density, and supporting other functions. This distinction matters because doctors can order different versions of the test depending on what they’re looking for.
A total testosterone test measures both the bound and free forms together. This is the standard first-line test and the one most guidelines use to define “low.” A free testosterone test measures only the unattached portion your body can actively use. It’s less commonly ordered but can help clarify the picture when total testosterone is borderline or when conditions like obesity or liver disease are affecting protein levels. A third option, the bioavailable testosterone test, captures free testosterone plus the portion loosely bound to a protein called albumin. This one is rarely ordered outside of specialty settings.
For most people, a total testosterone test is the starting point. If results are ambiguous, your doctor may add free testosterone to get a clearer read.
Normal Ranges and the Cutoff for “Low”
The American Urological Association defines healthy male testosterone as 450 to 600 ng/dL, with the clinical threshold for low testosterone set at below 300 ng/dL. Some labs report anything down to 264 ng/dL as normal, so the reference range on your lab printout may look slightly different depending on the laboratory. For adult men 18 and older, the broad normal range spans roughly 264 to 916 ng/dL.
Women have much lower levels. Premenopausal women typically fall between 10 and 55 ng/dL, while postmenopausal women range from 7 to 40 ng/dL.
A single low reading doesn’t equal a diagnosis. The AUA recommends that low testosterone be confirmed only after two separate blood draws, both taken in the early morning, ideally at the same lab using the same method. A formal diagnosis also requires the presence of symptoms alongside those low numbers. If your levels come back at 280 ng/dL but you feel fine, that’s a different clinical conversation than 280 ng/dL with fatigue, erectile dysfunction, and depressed mood.
Why Morning Testing Matters
Testosterone follows a daily rhythm. Levels peak between 7:00 and 10:00 a.m., then gradually decline throughout the day, hitting their lowest point in the evening before rising again overnight. In younger men (ages 30 to 40), morning levels run 30 to 35% higher than afternoon levels. That gap narrows with age, dropping to about 10% by age 70, but it’s still significant enough to skew results.
Current guidelines recommend testing between 8:00 and 9:00 a.m. to minimize the effect of this natural fluctuation. An afternoon blood draw could return a result that looks low simply because of timing, not because anything is actually wrong.
Do You Need to Fast?
Eating can temporarily suppress testosterone in some people, which is why many guidelines recommend fasting before the test. However, recent research has found no statistically significant difference between fasting and non-fasting testosterone levels in practice. One study comparing fasted and non-fasted samples in the same group of men found median testosterone values that were virtually identical.
The safest approach is still to fast if your doctor asks you to, since it keeps your results consistent with the reference ranges most labs use. But if you accidentally ate breakfast before your draw, it’s unlikely to invalidate the result entirely.
At-Home Test Kits: Screening, Not Diagnosis
Home testosterone kits, typically using a finger prick or saliva sample, have become widely available. They’re convenient, but they come with real accuracy limitations. Finger-prick samples show three to eight times more variability than a standard venous blood draw. The small volume of blood collected makes results more susceptible to contamination, clotting, and dilution from tissue fluid that seeps in when you squeeze your fingertip.
There’s also a specific pitfall for anyone using topical testosterone (creams or gels): residue on your fingertips can artificially inflate the result to the point of making it clinically meaningless.
Home kits can be a reasonable first step if you’re curious and want a general screening. But if a home test flags low testosterone, the next step is confirming with a proper venous draw at a lab before making any decisions about treatment.
Medications That Can Shift Your Results
Several common medications can raise or lower testosterone levels enough to affect test results. Long-term opioid use is one of the most well-documented causes of suppressed testosterone in men. Corticosteroids (often prescribed for inflammation or autoimmune conditions), certain blood pressure medications like spironolactone and verapamil, the heart drug digoxin, and some anti-seizure drugs can also push levels down.
On the other side, medications like finasteride (commonly used for hair loss or prostate enlargement), the anti-ulcer drug cimetidine, the anti-seizure medication valproic acid, and the anti-epileptic phenytoin can raise testosterone readings.
In women, barbiturates, clomiphene (a fertility drug), estrogen-containing medications, and valproic acid can all increase testosterone levels. If you’re on any of these medications, make sure your doctor knows before interpreting your results. A low or high reading may reflect the medication’s effect rather than your body’s natural production.
Getting the Most Accurate Result
To give yourself the best shot at a reliable number, schedule your blood draw for early morning, ideally between 7:00 and 10:00 a.m. Fast overnight if your doctor recommends it. Let the lab know about any medications or supplements you’re taking, including testosterone products. If the first result comes back low, expect your doctor to order a second test on a different day before drawing conclusions.
If you’re testing through a home kit, treat the result as a rough estimate. A normal result is reassuring but not definitive. A low result is worth following up on with a venous draw, not worth acting on by itself.