The short version: the symptoms of low testosterone are real but so nonspecific that the diagnosis depends almost entirely on the blood test — and the blood test is easy to get wrong. Testosterone peaks in the morning and declines through the day, so an afternoon sample can read low in a man whose levels are normal. One low reading is not a diagnosis; guidelines call for two morning samples on separate days. And several reversible causes should be addressed before committing to a therapy that is usually lifelong.
Below is how to get the test right, what should be measured alongside it, and what to deal with before starting treatment.
The symptoms are real but they are not specific
Fatigue, reduced libido, erectile difficulty, low mood, loss of muscle and strength, increased body fat, poor concentration, disturbed sleep. These are genuine consequences of testosterone deficiency.
They are also the consequences of depression, thyroid disease, anaemia, iron deficiency, sleep apnoea, poorly controlled diabetes, chronic stress and simply not sleeping enough. Every one of those is common, and several are more common than testosterone deficiency.
Which is why the symptoms tell you to investigate rather than what the answer is. They cannot carry the diagnosis on their own, and a questionnaire that concludes you have low testosterone without a blood test has concluded nothing.
Getting the test right
| Requirement | Why it matters |
|---|---|
| Morning sample, roughly 7am to 10am | Testosterone follows a daily rhythm peaking in the morning; reference ranges assume a morning draw |
| Two samples on separate days | Day-to-day variation is substantial; a single low value is unreliable |
| Not during acute illness | Illness temporarily suppresses testosterone and produces a false low |
| Not after a night of poor sleep or very heavy exercise | Both transiently lower levels |
| Fasting is generally preferred | Food intake can lower measured testosterone |
The most common way this goes wrong is a convenient afternoon appointment, a single reading, and a diagnosis. If you have been told your testosterone is low, check what time the sample was taken and whether it was repeated. If it was an afternoon draw done once, the result does not establish anything.
Total versus free testosterone
Most testosterone circulating in blood is bound to carrier proteins, principally sex hormone binding globulin, and in that bound state it is unavailable to tissue. Total testosterone measures the whole pool. Free testosterone estimates the fraction actually available.
Usually total testosterone is sufficient. It becomes misleading when SHBG is abnormal, which is common:
- SHBG is lowered by obesity, insulin resistance and type 2 diabetes. Total testosterone can then look acceptable while the available fraction is low.
- SHBG is raised by ageing, thyroid overactivity, liver disease and some medications. Total testosterone can then look reassuring or borderline while tissue availability is reduced.
Since obesity and insulin resistance are precisely the conditions that coexist with low testosterone symptoms, this is not an edge case.
What else belongs in the panel
Measuring testosterone alone tells you a level but not a cause.
| Test | What it tells you |
|---|---|
| LH and FSH | Whether the problem is in the testes or in the pituitary gland directing them |
| Prolactin | An elevated level can indicate a pituitary cause needing its own investigation |
| Full blood count | Baseline before treatment, which raises red cell concentration |
| Thyroid function | Produces overlapping symptoms and is far more common |
| Ferritin and iron studies | Iron deficiency causes fatigue that mimics this picture |
| HbA1c | Diabetes both contributes and produces overlapping symptoms |
| Vitamin D | Commonly low and contributes to fatigue and low mood |
| PSA where age-appropriate | Baseline before treatment |
Sleep apnoea deserves separate mention. It lowers testosterone, produces every symptom on the list, is extremely common in men with central weight gain, is frequently undiagnosed, and can be worsened by testosterone therapy. Screening for it before starting treatment is sensible rather than cautious.
Reversible causes worth addressing first
Testosterone therapy is generally a long-term commitment, so it is reasonable to attempt the reversible routes when the picture allows.
- Excess weight. Fat tissue converts testosterone to oestrogen, so significant weight loss raises testosterone in men with obesity. This is one of the few genuinely causal interventions available, and it is covered on our medically supervised weight loss page.
- Untreated sleep apnoea. Treating it improves levels and symptoms.
- Sleep duration. Most testosterone release happens during sleep; chronic short sleep measurably lowers it.
- Heavy alcohol use. Directly suppresses production.
- Medications. Opioids are a particularly common and reversible cause. Some steroids and other drugs contribute.
What treatment involves, including the downsides
Where deficiency is genuinely established and reversible causes have been addressed, treatment can make a real difference to energy, libido, mood and body composition. It is not without consequences, and these belong in the conversation before starting.
Therapy suppresses the body’s own production, which reduces sperm production and can affect fertility — important for any man who may want children, and the reason it is raised early. It raises red blood cell concentration, which requires periodic monitoring. It can worsen sleep apnoea, and may cause acne, fluid retention or breast tenderness. And because stopping returns levels to baseline or temporarily below it, this is usually an ongoing commitment rather than a course.
How we assess, what we test and how we monitor is on the hormone replacement therapy for men page, and the broader approach on the hormone optimization page.
A reasonable standard for any clinic offering this: two morning blood tests before a diagnosis, LH and FSH to establish the cause, a conversation about fertility before the first dose, and monitoring afterward. A single finger-prick test followed immediately by a prescription does not meet it.
Common questions
What time of day should testosterone be tested?
Early morning, generally between 7am and 10am. Testosterone follows a daily rhythm that peaks in the morning and falls through the day, and the reference ranges clinicians use were established on morning samples. An afternoon sample can read low in a man whose levels are entirely normal, which is one of the most common reasons for a misleading result.
Do I need more than one blood test?
Yes. Guidelines generally call for two separate morning measurements on different days before diagnosing testosterone deficiency. Levels vary day to day, and acute illness, poor sleep, recent heavy exercise and stress all temporarily suppress them. Diagnosing and treating from a single low reading is a frequent and consequential shortcut.
What is the difference between total and free testosterone?
Most testosterone in blood is bound to proteins, principally sex hormone binding globulin, and is not available to tissue. Total testosterone measures everything; free testosterone measures the unbound fraction. The distinction matters when SHBG is abnormal — obesity and insulin resistance lower it, while ageing, thyroid disease and some medications raise it — because total testosterone can then misrepresent what tissue is actually receiving.
What else should be checked alongside testosterone?
Luteinising hormone and FSH, which indicate whether the problem originates in the testes or in the pituitary; prolactin, since an elevated level can point to a pituitary cause; a blood count, because treatment raises red cell concentration; and often thyroid function, iron studies and vitamin D, as these produce overlapping symptoms. Screening for sleep apnoea is worthwhile, as it both lowers testosterone and worsens with treatment.
Can low testosterone be reversed without medication?
Sometimes, and it is worth attempting when the cause is reversible. Significant weight loss raises testosterone in men with obesity, as fat tissue converts testosterone to oestrogen. Treating sleep apnoea, improving sleep duration, reducing heavy alcohol use and reviewing medications such as opioids and some steroids can all help. These are addressed before committing to lifelong therapy where the picture allows.
What are the downsides of testosterone therapy?
It suppresses the body’s own production and can reduce sperm production and fertility, which matters for men who may want children. It raises red blood cell concentration, which needs monitoring. It can worsen sleep apnoea, cause acne and fluid retention, and in some men breast tenderness. Treatment is generally long term, since stopping returns levels to baseline or temporarily below it.
Reviewed by Daniel Moghadam, M.D., founder and medical director of Modern Aesthetica. Last reviewed October 2026. Testosterone deficiency requires biochemical confirmation and has several causes, some needing investigation in their own right. Therapy affects fertility and requires ongoing monitoring.
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