Hormones . Symptoms guide
Low Testosterone in Men: When to Test
Quick answer
Symptoms of low testosterone overlap with many other conditions, which is why a blood test is the only reliable way to confirm it. The most useful first step is total and free testosterone plus DHT, taken strictly between 7:00 AM and 11:00 AM while fasting, as levels naturally peak during these hours and drop significantly following food intake. Adding a Full Blood Count and thyroid check rules out key mimics like anaemia, while measuring pituitary hormones (LH, FSH and Prolactin) is vital to identify the structural root cause if your testosterone levels are low.
This patient information is being clinically reviewed by our team. The factual content draws on UK guidance (NHS, NICE, British Association of Dermatologists, and other specialist society guidance where cited).
What this might be
- Primary hypogonadism. Testicular failure (Klinefelter, post-mumps, trauma, chemotherapy).
- Secondary hypogonadism. Pituitary or hypothalamic causes; often reversible. LH, FSH and prolactin help localise the source.
- Age-related decline. Gradual fall from late 30s onward; symptoms become noticeable when levels drop below individual threshold.
- Lifestyle drivers. Poor sleep, obesity, chronic stress, opioid use, anabolic steroid recovery.
Common features that suggest this
- Low libido
- Erectile changes
- Reduced morning erections
- Persistent fatigue not explained by sleep
- Loss of muscle bulk despite training
- Mood changes, irritability, or low motivation
- Reduced beard or body hair growth
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
Need a marker not in these panels? Build a custom panel and a GMC-registered clinician will design one for you.
Markers your clinician will commonly look at
These are the individual blood markers in the recommended panels above. Click any to read what it measures, its UK reference range, and what high or low values mean.
Testing advice
Morning appointment strictly between 7:00 AM and 11:00 AM is essential. Testosterone follows a diurnal cycle and an afternoon sample may read up to 30 percent lower, leading to a misdiagnosis. Repeat testing on two separate days is recommended before any treatment decision.
Common questions
What is a normal testosterone level?
While standard UK laboratory reference ranges span from 8 to 30 nmol/L, British clinical guidelines (BSSM, in line with the Society for Endocrinology) state that levels below 12 nmol/L frequently warrant further investigation if you are experiencing symptoms of deficiency. Free testosterone and SHBG contextualise the picture.
Do I need to fast?
Yes. You must fast (water only) for at least 8 to 12 hours before your test. Consuming food or sugary drinks in the morning can temporarily drop your testosterone levels by up to 30 percent, leading to an inaccurate result. Avoid heavy alcohol the night before.
Should I stop my supplements?
Stop over-the-counter hormone supplements like DHEA or over-the-counter booster products 2 weeks before testing. However, if you are taking prescription testosterone replacement therapy (TRT), a 2-week break will not show your natural baseline due to ongoing pituitary suppression, and pausing TRT can cause significant symptom rebound. Do not alter a prescription regimen without clinical guidance from your prescriber.
Related symptoms
Sources and further reading
- British Society for Sexual Medicine: Testosterone deficiency guidelines
- Society for Endocrinology: Male hypogonadism
This page provides general information only and is not a substitute for medical advice. A GMC-registered clinician will review your results and tailor any recommendations to you personally.