In short
- Testosterone swings through the day. It is measured in the morning between 7 and 11 a.m., preferably fasting.
- One low value is not a diagnosis. Confirmation requires a second morning measurement on a different day.
- Total testosterone depends on SHBG. In obesity, SHBG is low. Total testosterone then looks low even though free testosterone is not.
- LH and FSH tell you where the cause is: in the testes or in the brain axis. That changes the management.
- The value is temporarily lowered by illness, lack of sleep, weight loss, opioids and overtraining. Do not measure during these.
Testosterone is the hormone that is easiest to measure wrongly. Three things go wrong most often: the time of the blood draw, relying on a single measurement, and reading total instead of free testosterone. That is why so many men end up with a number that does not mean what they think.
When measuring makes sense at all
Testosterone is not a screening test for all men. It makes sense when the signs that point to deficiency are present:
- Reduced sex drive and fewer morning erections.
- Erectile dysfunction, especially if it came on gradually.
- Loss of muscle mass and strength despite unchanged training.
- Persistent tiredness and low mood that other causes do not explain.
- Less body hair, tender breasts, smaller testes.
- Unexplained loss of bone density or a fracture from a minor force.
Tiredness on its own is a poor reason to measure testosterone. Far more often, iron, thyroid, sleep and sugar explain it. Measure all of these first.
How to measure correctly
| Rule | Why |
|---|---|
| In the morning between 7 and 11 a.m. | The value is highest in the morning and falls by up to a third by the afternoon. An afternoon measurement often shows a false deficiency. |
| Fasting | A meal, especially a sugary one, temporarily lowers the value. |
| Twice, on two different days | The value swings from day to day. A diagnosis of deficiency requires two low morning measurements. |
| Not during illness | Acute illness lowers the value markedly. Wait at least two weeks after recovery. |
| Not after a sleepless night or a heavy training week | Both temporarily lower the value. |
Which tests and what each one adds
| Test | Which question it answers | When |
|---|---|---|
| Total testosterone | How much hormone there is in the blood in total. | Always first. |
| SHBG | How much hormone is bound and therefore inactive. | With a borderline value, in obesity, thyroid disorders, liver disease. |
| Calculated free testosterone | How much hormone is available to the tissues. | Calculated from total, SHBG and albumin. More reliable than directly measured free testosterone. |
| LH and FSH | Whether the cause is in the testes or in the brain axis. | With confirmed deficiency. Changes the management. |
| Prolactin | Whether a pituitary hormone is suppressing the axis. | With low or normal LH despite low testosterone. |
| Ferritin, TSH, glucose | Whether something else explains the symptoms better. | Practically always worth doing alongside. |
Why SHBG changes the picture. In obesity and insulin resistance, SHBG is low. Total testosterone then looks low while free testosterone can be normal. The reverse is true in older men. SHBG is often high, so total looks acceptable while free is low. Reading total without SHBG is the most common mistake with this marker.
How to read the number
| Total testosterone | How it is read | What follows |
|---|---|---|
| Clearly within range | Deficiency unlikely. | Explain the symptoms elsewhere: sleep, iron, thyroid, sugar, mood. |
| Borderline low | Grey zone. On its own it does not say enough. | Repeat in the morning on another day, add SHBG and calculate free testosterone. |
| Clearly low on two morning measurements and with symptoms | Probable deficiency. | Talk to your doctor. LH and FSH show the cause. |
Cut-offs differ between laboratories and between guidelines. So in the app you always see the cut-off that was used and its source. The key point: a low number without symptoms is not a diagnosis. And symptoms without a low number are not a deficiency.
What lowers the value temporarily
- Excess weight. The most common correctable cause. Losing weight often raises the value without medicines.
- Chronic lack of sleep and untreated sleep apnoea.
- Opioid medicines and some other medicines that suppress the axis.
- A large energy deficit during weight loss or endurance training.
- Acute or chronic illness, including a recent infection.
- Past anabolic steroid use. The axis recovers slowly afterwards, sometimes incompletely.
For most men the first step is not a prescription. Weight, sleep and apnoea explain a large share of borderline values. Only once these are sorted out, and the value stays low, does a conversation about treatment make sense.
What treatment means and what it does not
Testosterone replacement therapy is a doctor's decision, not the report's. Before you decide on it, it is fair to know two things:
- It suppresses your own production and fertility. External testosterone reduces sperm production. If you are planning children, this changes the whole approach.
- It requires monitoring. During treatment, haematocrit, PSA in older men and testosterone itself are checked regularly.
Be cautious of offers that propose therapy straight away on the basis of a single afternoon measurement. The sequence is always the same: measure correctly, repeat, find the cause, fix what is correctable. Only then comes treatment.
Frequently asked questions
When should I measure testosterone?
In the morning between 7 and 11 a.m., preferably fasting. Not during illness or after a sleepless night. One value is not a diagnosis. A second morning measurement on a different day is needed.
Why do I need SHBG?
Because it determines how much hormone is available to the tissues. In obesity, SHBG is low and total testosterone looks low even though free testosterone is not. In older men it is often the other way round.
My testosterone is low but I feel fine. Is that a problem?
A low number without symptoms is not a diagnosis of deficiency. Check whether the measurement was taken in the morning, and repeat it before doing anything.
Can I raise testosterone without medicines?
For some men, yes. Losing excess weight, sorting out sleep and treating apnoea are the best-proven measures. Supplements that promise this mostly lack solid evidence.
Does treatment affect fertility?
Yes. External testosterone suppresses your own production and reduces sperm production. If you are planning children, be sure to tell your doctor before starting.
Sources: Endocrine Society — management of hypogonadism in men, morning blood draw and confirmation with a second measurement · EAU — guidelines on male sexual and reproductive health · EAA — the role of SHBG and calculated free testosterone · ESE — the effect of obesity and obstructive sleep apnoea on the axis · our knowledge base (age bands).
