Low Testosterone: How It Is Properly Diagnosed, and How Treatment Is Monitored

More men than ever are ordering a testosterone test, seeing one number below a lab range, and concluding they need treatment. Sometimes they are right. Often the picture is more complicated, because low testosterone is a clinical diagnosis that combines symptoms with correctly measured, confirmed blood levels, and because starting treatment without the right checks and follow-up is where people get into trouble. Here is how it is actually done, based on the guidelines that specialists work from.

Low testosterone is a diagnosis, not a number

Testosterone deficiency, or male hypogonadism, is defined as persistently low testosterone together with symptoms that fit.¹ That second half matters. Plenty of men sit slightly below a reference range and feel perfectly well, and plenty of the symptoms blamed on low testosterone, low energy, low mood, poor concentration, reduced libido, loss of muscle and gain in body fat, have several possible causes. A diagnosis is made when the symptoms and the biochemistry point the same way, not when a single figure looks low on a screen.¹²

How the diagnosis is actually confirmed

The blood side of the diagnosis follows a specific method:

• A fasting, morning sample. Testosterone runs on a daily rhythm and peaks in the morning, so that is when it is measured for an accurate reading.¹
• Confirmed on a repeat. A single low result can be a blip. Both the Endocrine Society and the American Urological Association define deficiency as a total testosterone below 300 ng/dL (about 10.4 nmol/L), confirmed on a second morning test before any diagnosis is settled.¹³
• Free testosterone when the total is borderline. When the total testosterone sits near the lower limit, or when the carrier protein SHBG is high or low, free testosterone estimated by a validated method gives a truer read than the total alone.¹
• LH and FSH to find the cause. These pituitary hormones separate the two very different forms of the condition, which is the next section.¹

Why the cause matters: primary versus secondary

Two men can have the same low testosterone for opposite reasons, and the difference changes the right course of action.¹ In primary hypogonadism, the testes themselves are underproducing, and the brain responds by driving LH and FSH high in an attempt to compensate. In secondary hypogonadism, the signal from the brain and pituitary is the problem, so LH and FSH are low or normal despite the low testosterone. When those pituitary hormones are low, further evaluation, such as a prolactin level, is used to look for a treatable cause. Identifying which form is present is not academic: it guides whether replacement is appropriate, whether fertility can be protected, and whether something else needs treating first.¹

What has to be checked before starting treatment

Testosterone therapy is not started on the strength of a low result alone. A proper baseline includes a hematocrit, the proportion of your blood made up of red cells, because testosterone can raise it, and a PSA in men 40 and older, because prostate health has to be accounted for.¹ A baseline hematocrit above 48% is a reason not to start.¹ Treatment is also generally avoided in men who are planning to conceive in the near future, since testosterone therapy suppresses natural sperm production, and in men with recent heart attack or stroke, untreated severe obstructive sleep apnea, or known prostate or breast cancer.¹ This is the assessment that a home test kit cannot do for you, and skipping it is how avoidable harm happens.

What treatment does, and does not, reliably do

Honesty about the benefits is part of good care. In properly diagnosed men, testosterone therapy has been shown to improve sexual function and depressive symptoms, and to increase bone density and lean body mass.¹ It is also honest to say where the evidence is weaker: large trials found benefit for sexual function and some benefit for mood, but no clear benefit for vitality or walking distance, and the American College of Physicians advises discussing treatment mainly to improve sexual function rather than for energy, physical function, or cognition.¹⁴ On the safety question that worries most men, the large TRAVERSE trial found testosterone was noninferior to placebo for major cardiac events in men at high cardiovascular risk, though it recorded more atrial fibrillation and pulmonary embolism in the treated group.⁵ We cover that cardiovascular evidence in depth in Is Testosterone Therapy Safe?

How a properly monitored protocol works

This is the part that separates a considered protocol from a prescription handed over and forgotten. The goal is to bring testosterone into the mid-normal range and, above all, to improve how you actually feel, while watching for the predictable effects of treatment.¹ In practice that means rechecking serum testosterone and hematocrit at around 3 to 6 months and then at least once a year, with PSA reassessed after starting and at least annually in older men.¹ A hematocrit that climbs too high is the effect watched most closely: a value above 54% is a signal to pause treatment and involve a blood specialist.¹ None of this is exotic, but it has to be done consistently, and it is the reason testosterone is best managed as an ongoing, supervised relationship rather than a one-off script.

Everything above starts with reading the right markers correctly in the first place, which we cover in What a Proper Men's Health Blood Panel Actually Measures, and it is worth knowing who is best placed to oversee testosterone treatment before you begin.

A candid word on the noise around testosterone. There is no shortage of confident advice about it online, from influencers, coaches, and forums, much of it from people who will also sell you a protocol or the vials themselves. Naming the compounds and reciting doses is the easy part, and plenty of people do it with great confidence. What a physician brings is different in kind: a real understanding of the physiology, of who genuinely needs treatment and who does not, and the training to recognize, diagnose and treat what can go wrong, a climbing hematocrit, blood pressure, fertility, estrogen, cardiovascular strain. That is the whole point, because it is precisely the moment the confident voices tend to fall quiet and tell you to see a doctor. We would simply rather be the doctor who set it up properly than the one you are sent to once something has already gone wrong.