Education
What Is Low Testosterone?
Written and reviewed by Dr. Slava Fuzayloff, DO · Board-Certified Internal Medicine · Last updated: July 2026
Education
Written and reviewed by Dr. Slava Fuzayloff, DO · Board-Certified Internal Medicine · Last updated: July 2026
What is low testosterone? Low testosterone (also called "low T") means your body doesn't make enough testosterone, the main male sex hormone. Most guidelines mark the line at a total testosterone under 300 nanograms per deciliter (ng/dL). But the number alone isn't the whole story — how you feel matters too.
Testosterone controls sex drive, energy, muscle, mood, and bone strength. Levels drop slowly with age, so low T is common. The medical name for it is hypogonadism. In plain terms, the low testosterone meaning is simple: not enough usable testosterone to keep your body running the way it should. A single low reading doesn't settle it, and — as you'll see below — a "normal" total number can still hide a real problem.
Total testosterone is all the testosterone in your blood. Free testosterone is the small part — usually 2–3% — that isn't attached to proteins and is the part your body can actually use. Most of your testosterone is bound up and unavailable, so the free number often tells you more than the total.
| Total testosterone | Free testosterone | |
|---|---|---|
| What it measures | All testosterone in your blood | Only the unbound, usable part (about 2–3%) |
| Bound to proteins? | Includes bound and unbound amounts | No — this is the free portion |
| Why it matters | The standard first test | Often a better match for how you feel |
Most of your testosterone is stuck to a protein called SHBG (sex hormone-binding globulin) and can't be used. When SHBG is high, it locks up more testosterone — so your total can look fine while the free, usable amount is low.
Yes. You can have a total testosterone that looks normal on paper and still have low free testosterone — the part your body uses. This usually happens when SHBG is high and binds up too much of your testosterone. It's the most-missed cause of low T, and it's why a "normal" result doesn't always rule the problem out.
Because of this, the Endocrine Society recommends checking free testosterone when the total sits near the low end of normal, or when SHBG may be off — such as in men who are older, obese, or have diabetes or thyroid disease. If your total came back "normal" but you still have symptoms, a free testosterone test is the next step.
How is low testosterone diagnosed? It takes two things together: a genuinely low lab result and real symptoms. The number alone isn't enough. Many men with low readings feel fine, and treatment is only appropriate when low levels and symptoms line up.
This cuts both ways. A low number with no symptoms usually isn't treated. Symptoms with a truly low, confirmed number point to low T. That's why a good evaluation looks at the labs and how you actually feel — not one without the other.
One low result doesn't confirm low testosterone. Levels swing during the day and peak in the morning, so a single reading — especially an afternoon one — can be misleading. Doctors confirm low T with at least two morning blood draws before making the diagnosis.
Testosterone follows a daily rhythm: highest early, lower by evening. A reliable test is drawn in the morning, and it's repeated on a separate day to rule out a one-off dip. If both morning draws come back low and you have symptoms, that's a real diagnosis.
Low free testosterone comes from either making less testosterone or binding up too much of it. High SHBG is a leading cause of a normal total but low free — and SHBG rises with age, thyroid problems, and liver conditions. Aging, obesity, diabetes, and chronic illness also lower usable testosterone.
Because a "normal" number can still hide low T, it's worth having your full picture read by a physician. Dr. Slava Fuzayloff, DO personally evaluates every new patient in person and reviews your total, free, and SHBG together with how you feel. Book online or call (212) 696-5900.
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