Low Testosterone Symptoms in Men: Diagnosis, Causes and Next Steps
Updated: Aug 18
Key point: low testosterone—or male hypogonadism—is diagnosed when compatible symptoms occur with consistently low testosterone measured correctly. Fatigue, low mood or one low blood result alone is not enough because each can have many other causes.
Which symptoms are most suggestive of low testosterone?
Sexual symptoms are usually the most specific: reduced sexual desire, fewer spontaneous or morning erections and erectile difficulty. Other possible features include reduced energy, low mood, reduced muscle strength, increased body fat, reduced body hair, hot flushes, infertility or low bone density.
These symptoms are not unique to testosterone deficiency. Poor sleep, depression, thyroid disease, anaemia, diabetes, obesity, chronic illness, medicines and relationship or psychological factors can produce a similar picture.
What causes testosterone deficiency?
Primary hypogonadism begins in the testes. Possible causes include genetic conditions, previous undescended testes, testicular injury or infection, chemotherapy, radiotherapy and some systemic diseases.
Secondary hypogonadism results from reduced pituitary or hypothalamic stimulation. Causes include pituitary disease, high prolactin, some medicines—particularly opioids—previous anabolic-steroid use and certain genetic or chronic conditions.
Testosterone can also be functionally suppressed by obesity, poor sleep, acute illness, uncontrolled metabolic disease or other health stressors. Identifying the cause matters because a reversible contributor may improve without lifelong replacement therapy.
How should testosterone be tested?
EAU guidance recommends measuring total testosterone between 07:00 and 10:00 while fasting, using a reliable laboratory assay. A low value should be repeated on a separate morning before diagnosis or treatment.
The EAU uses total testosterone below 12 nmol/L as a practical threshold in symptomatic men, but the number is never interpreted alone. Timing, illness, laboratory method, symptoms and conditions that alter sex hormone-binding globulin all affect interpretation.
Which additional blood tests may be needed?
LH and FSH help distinguish a testicular cause from a pituitary or hypothalamic cause. SHBG and calculated free testosterone can help when total testosterone and symptoms do not match, or when obesity, ageing, liver disease, thyroid disease or medicines may alter SHBG.
Prolactin is considered when secondary hypogonadism, low sexual desire or pituitary disease is suspected. Full blood count, glucose or HbA1c, lipids, thyroid tests and other investigations are selected according to the clinical picture. Severe secondary deficiency, new headaches or visual-field symptoms may require pituitary imaging.
Low testosterone, erectile dysfunction and general health
Testosterone deficiency can contribute to reduced desire and milder erectile problems, but erectile dysfunction is often multifactorial. Blood pressure, diabetes, lipids, smoking, medicines, sleep, vascular health and psychological factors should also be reviewed.
If morning erections are the main concern, read No Morning Erections: When Should You Be Concerned?.
The fertility warning before TRT
External testosterone can markedly reduce or stop sperm production. It should not be used to treat male infertility and should not be started in a man actively trying to conceive. Fertility goals must be discussed before gels or injections are prescribed.
See the guide to male fertility signs and testing.
What happens after diagnosis?
Treatment depends on symptoms, cause, fertility plans, health risks and preference. Reversible contributors such as obesity, poor sleep, uncontrolled diabetes or a relevant medicine may need treatment first or alongside hormone care.
Testosterone replacement may be considered when symptoms and repeat results confirm hypogonadism and there is no contraindication. It is not an anti-ageing, bodybuilding or general vitality treatment for men with normal testosterone.
For benefits, contraindications, formulations and monitoring, read Low Testosterone Treatment in London: Diagnosis, TRT and Fertility.
Frequently asked questions
Can low testosterone be diagnosed from symptoms alone?
No. Symptoms guide testing, but diagnosis requires consistently low, correctly timed testosterone results and assessment of other possible causes.
Is one low result enough?
Usually not. Testosterone varies with time of day, meals, sleep and illness. A low fasting morning value should be repeated on another morning.
Does ageing automatically mean I need TRT?
No. Testosterone may decline with age, but treatment is based on clinically relevant symptoms, confirmed deficiency, cause and individual risk—not age alone.
Can low testosterone cause infertility?
Some causes of hypogonadism can impair sperm production. External testosterone can suppress it further, so fertility-focused assessment is essential before treatment.
When should symptoms be assessed urgently?
Urgent review is appropriate for a new testicular lump, sudden severe testicular pain, or severe headache and visual symptoms with suspected pituitary disease. Otherwise, persistent sexual or systemic symptoms merit a planned clinical assessment.
Low testosterone assessment in London
A consultant-led assessment can review symptoms, repeat correctly timed tests, identify the cause and plan treatment while protecting fertility. Book a confidential appointment or email info@holisticandrology.com.
Clinical source
About the author
Prof Fabio Castiglione, MD, PhD, FECSM, FEBU, Urologist (ITA). Consultant Urologist and Andrologist — King’s College Hospital NHS Foundation Trust; Hon. Reader, King’s College London, UK; Academic Lead of Urology; GMC 7542824; Director and Founder of Holistic Andrology.
Medical information is educational and does not replace an individual consultation, examination or diagnosis.
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