Low Testosterone: What the Number Means, and How It Is Properly Diagnosed

There is a real medical condition here, it has a proper definition, and it is diagnosed in a specific way that most of the clinics advertising to you do not follow. Knowing the difference is worth more than anything else on this page.

What testosterone level counts as low?

The American Urological Association’s guideline sets the threshold plainly: a total testosterone below 300 ng/dL is a reasonable cut-off supporting a diagnosis of low testosterone. That is a moderate recommendation on Grade B evidence: a sensible line, not a law of nature.

The next statement is the one that matters more, and it carries the guideline’s strongest rating. Diagnosis requires two total testosterone measurements, taken on separate occasions, both in the early morning. Strong recommendation, Grade A evidence.

There is a straightforward physiological reason. Testosterone follows a daily rhythm, peaking in the early morning and falling through the day. A blood draw at four in the afternoon can put a perfectly normal man under 300 ng/dL. Levels also swing day to day in the same individual. One test tells you about one moment.

If a clinic tested you once, at whatever time you happened to walk in, and then offered you treatment, they did not diagnose you. They measured you.

Can you diagnose low T from symptoms?

The guideline’s third statement requires low testosterone combined with symptoms or signs. Both halves are necessary, and the reason is that the symptom list is almost uselessly non-specific on its own.

Low energy. Reduced libido. Difficulty concentrating. Low mood. Loss of muscle, gain of fat. Poor sleep.

Every one of those is also produced by depression, sleep apnoea, thyroid disease, anaemia, a demanding job, a new baby, or simply being tired. The entire “low T” marketing category rests on the fact that this list describes a very large share of men over forty at any given moment. Recognising yourself in it is not evidence of anything.

The reverse is also true and less often said: a man can have a testosterone of 250 ng/dL and no symptoms, and the guideline does not consider that a condition requiring treatment.

What should be checked before starting treatment?

Two things, and both are strong recommendations rather than optional extras.

Haemoglobin and haematocrit. Testosterone stimulates red blood cell production, and a meaningful number of men on treatment develop polycythaemia: blood that is too thick. The guideline requires measuring these before starting and informing the patient of the risk. Strong recommendation, Grade A.

PSA, in men over 40. A clinical principle, to exclude an existing prostate cancer before starting. This is not the same as saying testosterone causes prostate cancer. The modern evidence does not support that, but you do not want to begin treatment with an undiagnosed cancer already present.

Once on treatment, levels should be measured every six to twelve months.

What does testosterone treatment actually fix?

The most useful evidence here comes from the Testosterone Trials: 790 men aged 65 and over, across twelve US sites, in a coordinated set of randomised trials. The results were mixed in a way that is genuinely informative.

That pattern is worth sitting with, because it is close to the inverse of how testosterone is marketed. The thing it reliably improved was libido. The things it did not improve were energy and physical capability, which are precisely what the advertising promises.

When the trials’ data were pooled, walking speed and distance did show some improvement, and there was some benefit for mood and depressive symptoms. But the individual trials designed to answer those questions came back negative, and that is the more conservative reading.

What testosterone does for erections specifically is a narrower question with a clearer answer, covered in testosterone, libido and erections.

Is testosterone therapy bad for your heart?

For years the honest answer was that nobody knew. The AUA guideline still reflects that, requiring clinicians to counsel patients that it cannot be stated definitively whether testosterone therapy increases or decreases cardiovascular risk.

Then the TRAVERSE trial reported. It randomised 5,204 men aged 45 to 80, all with symptomatic hypogonadism confirmed by two fasting morning measurements under 300 ng/dL, and all with existing cardiovascular disease or high risk of it. Dosing targeted 350 to 750 ng/dL. Mean follow-up was 33 months.

The primary result: major adverse cardiac events occurred in 7.0% on testosterone against 7.3% on placebo: a hazard ratio of 0.96, meeting the criteria for non-inferiority. On the specific question of heart attacks and strokes, testosterone did not make things worse.

Three other findings were less reassuring and get quoted far less often:

• Atrial fibrillation: 3.5% on testosterone versus 2.4% on placebo
• Acute kidney injury: 2.3% versus 1.5%
• Pulmonary embolism: 0.9% versus 0.5%

And there is a boundary on what the trial can tell you. It studied men with a confirmed diagnosis, on carefully monitored doses aimed at a normal range. It says nothing about younger men, men without hypogonadism, athletes using supraphysiological doses, or anyone taking testosterone without the monitoring the trial provided. A result obtained under strict conditions does not transfer to a clinic that skips them.

Does testosterone therapy affect fertility?

Exogenous testosterone suppresses your body’s own production, and with it, sperm production. This is not a rare side effect. It is the mechanism, testosterone was studied as a male contraceptive for exactly this reason.

The guideline is unambiguous. The long-term impact on sperm production must be discussed with any patient interested in future fertility, and testosterone should not be prescribed to men currently trying to conceive. Both are strong recommendations on Grade A evidence.

Recovery data offer some reassurance, with caveats. In men who had normal fertility to begin with, the likelihood of returning to a sperm concentration of 20 million per millilitre was 67% at six months after stopping, 90% at twelve months, and 100% at twenty-four. But those figures come from contraception studies in men with normal baseline function. Among men who became azoospermic while on testosterone therapy, roughly 65% recovered.

If you might want children, this belongs in the conversation before the first injection, not after.

How do you tell a real assessment from a sales funnel?

Four questions answer it.

Did they test twice, both times in the early morning? If not, there is no diagnosis, whatever the paperwork says.

Did they check haematocrit and, if you are over 40, PSA, before prescribing? The guideline requires it.

Did anyone ask whether you want children? A prescriber who does not ask is not following the guideline.

Did anyone look for a cause? Obesity, poor sleep, alcohol and opioids all lower testosterone, and several of them are reversible. If you are carrying significant excess weight, losing it raises testosterone measurably, see what actually raises testosterone naturally, where the numbers are larger than most men expect.

And if you are considering a supplement instead, the testing on testosterone boosters is not encouraging.

This article is for information only and is not medical advice. It cannot account for your individual circumstances. Talk to a doctor about your own situation, particularly before starting or stopping any prescription medication.