A testosterone lab report typically shows a number in nanograms per deciliter (ng/dL), a reference range printed beside it, and possibly separate lines for total, free, or bioavailable testosterone. Understanding what each of these means, and why the reference range on your report might not tell the whole story, is the key to making sense of your results.
Total, Free, and Bioavailable Testosterone
All the testosterone in your blood is either bound to proteins or floating unattached. Your lab report may include one, two, or all three of the following measurements, and each one captures a different slice of that picture.
Total testosterone is the most commonly ordered test. It measures everything: testosterone bound to proteins plus testosterone circulating freely. This is the number most reference ranges and clinical guidelines are built around.
Free testosterone measures only the small fraction (roughly 2 to 3% in men) that isn’t attached to any protein. Because it’s unbound, free testosterone can enter cells and do its job directly. This number matters most when your total testosterone falls in a borderline or ambiguous range.
Bioavailable testosterone sits between the two. It includes free testosterone plus testosterone loosely attached to a protein called albumin. That loose bond breaks easily, so albumin-bound testosterone is still readily available to your tissues. The tightly bound portion, held by a protein called SHBG (sex hormone-binding globulin), is excluded because it’s essentially locked up and unavailable.
Why SHBG Changes Everything
SHBG acts like a sponge for testosterone. The more SHBG in your blood, the more testosterone gets locked up, and the less is free to actually work. This is why two people with the same total testosterone number can feel completely different: one may have low SHBG (leaving plenty of testosterone available) while the other has high SHBG (leaving very little).
Several common situations shift SHBG levels. Aging, liver disease, and hyperthyroidism tend to raise SHBG. Obesity, insulin resistance, and hypothyroidism tend to lower it. Estrogen-containing medications like oral birth control can push SHBG significantly higher in women. When any of these factors are present, free testosterone gives a more accurate picture of what your body is actually working with than total testosterone alone. Research published in the Journal of Clinical Endocrinology & Metabolism found that the percentage of testosterone that remains free is strongly tied to SHBG levels, with correlation values above 0.80 in both men and women.
If your report includes a calculated free testosterone (rather than a directly measured one), keep in mind that the calculation depends on accurate SHBG and total testosterone measurements. Unusual circumstances, like very high levels of other hormones competing for the same binding proteins, can throw calculated estimates off.
Reference Ranges for Men
Most labs print a reference range of roughly 250 to 1,100 ng/dL for adult men, but that wide window groups together 20-year-olds and 70-year-olds. Age-specific data gives a much clearer benchmark. A study published in the Journal of Urology analyzed testosterone in healthy men aged 20 to 44 and found these middle-of-the-road ranges:
- Ages 20 to 24: 409 to 558 ng/dL
- Ages 25 to 29: 413 to 575 ng/dL
- Ages 30 to 34: 359 to 498 ng/dL
- Ages 35 to 39: 352 to 478 ng/dL
- Ages 40 to 44: 350 to 473 ng/dL
Notice the gradual decline. A 40-year-old with a total testosterone of 370 ng/dL sits comfortably in the normal zone for his age, even though he’d be below average for a 25-year-old. The Endocrine Society uses 264 ng/dL as the lower cutoff for diagnosing testosterone deficiency in men, based on standardized testing in healthy, non-obese young adults. That said, the threshold is meant as a starting point, not a verdict on its own.
Testosterone Ranges for Women
Interpreting testosterone in women is trickier because there is no universally agreed-upon “normal” value. Levels are much lower than in men (typically in the range of 15 to 70 ng/dL, depending on the lab), and they decline steadily starting in the 30s. What counts as low for a 30-year-old is a different number than what counts as low for a 50-year-old.
Low testosterone in women can show up as reduced sex drive, persistent fatigue, loss of muscle tone, irregular periods, vaginal dryness, thinning hair, or difficulty sleeping. On the other end, elevated testosterone may cause acne, excess hair growth on the face or body, thinning hair on the scalp, a deeper voice, or irregular cycles. Conditions like polycystic ovary syndrome (PCOS) are a common reason testosterone runs high in women.
Units on Your Report
Labs in the United States typically report testosterone in ng/dL (nanograms per deciliter). Labs in most other countries use nmol/L (nanomoles per liter). If you’re comparing your results to a reference you found online and the units don’t match, multiply ng/dL by 0.0347 to convert to nmol/L. So a reading of 400 ng/dL equals about 13.9 nmol/L. The Endocrine Society’s 264 ng/dL cutoff, for example, converts to 9.2 nmol/L.
When Your Blood Was Drawn Matters
Testosterone follows a daily rhythm. Levels peak in the early morning and drop throughout the day, sometimes by 20 to 30% by late afternoon. For this reason, blood draws for testosterone are best done in the morning. Some providers also ask you to fast beforehand, since eating can temporarily affect hormone levels. If your blood was drawn at 3 p.m. after lunch, a borderline-low result may not reflect your actual baseline.
Clinical guidelines also call for at least two separate low readings before drawing conclusions. A single test can be thrown off by a bad night of sleep, recent illness, intense exercise, or stress. Repeating the test on a different morning confirms whether the pattern is real.
Testing Methods Aren’t All Equal
Two main laboratory techniques are used to measure testosterone: immunoassay and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Immunoassay is cheaper and works well at higher concentrations, which makes it reasonable for most men. LC-MS/MS is more accurate across a wider range of values, especially at the low end. This makes it the preferred method for women, children, and anyone expected to have low levels. If your result seems inconsistent with your symptoms, ask whether the test was run by immunoassay. A retest using mass spectrometry may give a more reliable number.
For free testosterone specifically, direct measurement by equilibrium dialysis combined with mass spectrometry is considered the reference standard. Many labs instead calculate free testosterone from your total testosterone and SHBG using a formula, which is less expensive but slightly less precise.
Numbers vs. Symptoms
A testosterone level that falls within the reference range doesn’t automatically mean everything is fine, and a number slightly outside the range doesn’t automatically mean something is wrong. The Endocrine Society’s guidelines emphasize that a diagnosis of testosterone deficiency requires both consistently low levels and symptoms that match, things like low energy, reduced sex drive, loss of muscle mass, depressed mood, or difficulty concentrating.
This matters most in the gray zone. If your total testosterone is 280 ng/dL and you feel great, that number alone isn’t a diagnosis. If it’s 310 ng/dL and you have clear symptoms along with low free testosterone, the clinical picture may point toward deficiency even though total testosterone is technically above the 264 ng/dL cutoff. Context, including your age, weight, other medical conditions, and SHBG level, shapes what the number actually means for you.