Testosterone blood test: what it measures and what can change it
Testosterone is the main male sex hormone, made mostly in the testicles. It is highest in the morning and lower after food, poor sleep or illness.
General information about the test, from Hea's guide and the NHS · Last reviewed 5 November 2026
What it measures, and why GPs check it
Testosterone is the main male sex hormone, made mostly in the testicles. It is highest in the morning and lower after food, poor sleep or illness.
It is measured when a man has symptoms such as a lower sex drive or erection problems; guidelines advise against testing men without symptoms.
Levels in UK guidance
Ranges differ between labs — your report shows your lab's range.
- UK laboratory guidance uses a morning, fasting sample taken when a man is well: a result after 11am, after food or during an acute illness is not used to diagnose low testosterone. Society for Endocrinology and ACB position statement 2023 (PMID 37391940), Panel 1
- A single low result is not enough: about 30% of men with a low first result have a normal one on repeat, so guidelines ask for two morning samples. Endocrine Society 2018 (PMID 29562364) 1.1; BSSM 2023 (PMID 36876744); EAU 2026, 3.3.5
- Sources differ on the level that counts as low in a man with symptoms: below 8 nmol/L, with 8–12 nmol/L a grey zone (UK position statement); below 12 nmol/L (other British and European guidelines). UK laboratories print lower limits from 4.9 to 11 nmol/L. Society for Endocrinology and ACB position statement 2023 (PMID 37391940), Panel 1; BSSM 2023, Table 4; EAU 2026, 3.3.5
- Obesity, type 2 diabetes, opioid painkillers, long-term steroid tablets and anabolic steroids lower testosterone; with obesity or diabetes the total can read low while free testosterone is normal. Endocrine Society 2018 (PMID 29562364), Tables 1 and 2; Society for Endocrinology 2022 (PMID 34811785), 2.11–2.17
What can shift the number
Before the test
- Ate in the 8 hours before. Food lowers testosterone: a result after a meal can read lower, and UK laboratory guidance asks for a fasting morning sample. Society for Endocrinology and ACB position statement 2023 (PMID 37391940), Panel 1; BSSM 2023 (PMID 36876744)
- A short night before the test, or I work night shifts. Testosterone follows sleep, not the clock: it reads lower after a short night, and night-shift workers may not have the morning peak. Society for Endocrinology and ACB position statement 2023 (PMID 37391940)
Now or in the last 3 months
- An infection or illness in the 6 weeks before. Testosterone falls during an acute illness: guidelines advise against testing a man who is ill or still recovering. Society for Endocrinology and ACB position statement 2023 (PMID 37391940), Panel 1; Endocrine Society 2018 (PMID 29562364) 1.1
Some medicines and supplements can change this result too. When you add your results, Hea asks which ones you take.
What a GP reads it with
Read together with: SHBG, LH, FSH, Prolactin. Society for Endocrinology and ACB position statement 2023 (PMID 37391940); Endocrine Society 2018 (PMID 29562364) 1.3, 1.4
A GP usually repeats it on a morning before breakfast with LH, FSH, SHBG and prolactin, asks about symptoms, weight, sleep and medicines, and refers to an endocrinologist when low testosterone is suspected.
Questions to ask your GP
- Was this sample taken at the right time of day, and fasting, for the result to count?
- Should it be repeated, together with LH, FSH, SHBG and prolactin?
- Could my weight, sleep or a medicine I take explain this result?
Safety first
If your lab or GP has flagged your result as urgent, follow their advice first.
Not for emergencies: call 999 or NHS 111.
Questions people ask
Why would a GP do a testosterone test?
A GP may check testosterone when a man has symptoms such as low sex drive, erection problems, low mood or a lack of energy. These symptoms often have other causes, such as stress, anxiety, depression, poor sleep or alcohol. So the GP usually asks about your work and personal life as well.
NHS: The 'male menopause', Page last reviewed 13 October 2022Do testosterone levels drop with age?
Yes, but slowly. The NHS says testosterone falls by about 1% a year from around the age of 30 to 40, and this is unlikely to cause problems on its own. A real deficiency later in life, called late-onset hypogonadism, is uncommon and does not come with age alone.
NHS: The 'male menopause', Page last reviewed 13 October 2022What time of day should a testosterone test be done?
In the morning. Testosterone is highest in the morning and lowest in the late afternoon and evening. So your doctor may ask for the sample early in the morning, at about 9am.
Lab Tests Online UK: Testosterone test, Page updated 23 March 2026What happens after a low testosterone result?
Your GP reads the result together with your symptoms. If the results suggest a deficiency, the NHS says you may be referred to an endocrinologist, a specialist in hormones. If the specialist confirms it, you may be offered treatment to replace the hormone.
NHS: The 'male menopause', Page last reviewed 13 October 2022How can I increase my testosterone levels?
Start with your GP, who looks for the cause of your symptoms first. The NHS lists lack of sleep, a poor diet, too little exercise, too much alcohol, smoking and stress among the common causes of the same symptoms. Low testosterone later in life is more common in men who are obese or have type 2 diabetes. Hormone treatment may be offered if a specialist confirms a deficiency.
NHS: The 'male menopause', Page last reviewed 13 October 2022Got your result? Start with this question in your AI.
Join Hea, add it to Claude or ChatGPT, and your chat opens with this question ready. Hea shows what the lab printed, your past results and what can shift a number; your GP decides what it means for you.
Hea, my testosterone result came back — help me understand it with my history
Closed beta for adults (18+) living in the UK. Free in the beta.
Sources
Each line about the test above names the guideline it comes from, as Hea's guide cites it. The answers to the questions come from:
- NHS: The 'male menopause', Page last reviewed 13 October 2022
- Lab Tests Online UK: Testosterone test, Page updated 23 March 2026