Low Testosterone Symptoms: When to Get a Blood Test

Low testosterone affects an estimated 1 in 4 men at some point in their lives, yet the majority never receive a diagnosis. A UK cross-sectional survey found that nearly half of men screened showed a high likelihood of testosterone deficiency, but only 5% had been formally diagnosed. The symptoms creep in gradually — a little more fatigue, slightly lower motivation, a reduced sex drive — and are often dismissed as “just getting older.”

They shouldn’t be. Low testosterone symptoms are clinically significant, measurable through a simple blood test, and in many cases treatable. This guide explains what to look for, what the blood tests reveal, and when it’s time to act.

What Is Low Testosterone?

Testosterone is the primary male sex hormone, produced mainly in the testes. It governs sex drive, sperm production, bone density, muscle mass, fat distribution, red blood cell production, and mood regulation. Women also produce testosterone (in the ovaries and adrenal glands), though at roughly one-tenth the concentration.

Low testosterone — clinically termed testosterone deficiency or hypogonadism — occurs when blood levels fall below the reference range AND symptoms are present. The BSSM emphasises that abnormal biochemistry alone is not sufficient for diagnosis: you need both low levels and clinical symptoms.

In the UK, the prevalence sits between 8% and 12% of men over 40, rising with age and comorbidities such as type 2 diabetes and obesity.

Low Testosterone Symptoms in Men

The symptoms of low testosterone are wide-ranging because testosterone receptors exist throughout the body. Symptoms typically develop gradually, which is partly why they are so often overlooked.

1. Persistent Fatigue and Low Energy

Not ordinary tiredness after a poor night’s sleep — but a deep, unrelenting fatigue that does not resolve with rest. Men with low testosterone frequently report feeling exhausted by mid-afternoon, regardless of how much sleep they had. This fatigue can also be driven by low ferritin, anaemia, or thyroid dysfunction, which is why a comprehensive blood panel matters.

2. Low Libido

A marked decline in sexual desire is one of the hallmark low testosterone symptoms. This goes beyond occasional dips — it is a sustained loss of interest that often affects relationships and self-confidence.

3. Erectile Dysfunction

While testosterone is not the only factor in erectile function, it plays a crucial role. Low levels reduce nitric oxide signalling, making erections harder to achieve and maintain. It is worth noting that erectile dysfunction can also be an early marker for cardiovascular disease, reinforcing the value of a full health screen.

4. Brain Fog and Poor Concentration

Difficulty concentrating, memory lapses, and a general sense of mental cloudiness are commonly reported. Testosterone influences cognitive function through its effects on neurotransmitter activity and cerebral blood flow. Low vitamin D can produce similar cognitive symptoms and is often found alongside low testosterone.

5. Mood Changes, Irritability, and Low Motivation

Depression, irritability, anxiety, and a noticeable drop in motivation or drive are frequently linked to testosterone deficiency. Some studies suggest that low testosterone doubles the risk of depressive symptoms in older men. These mood changes are often the symptom that finally prompts men to seek help.

6. Loss of Muscle Mass and Strength

Testosterone is anabolic — it drives muscle protein synthesis. When levels drop, men notice decreased muscle mass and strength, even when maintaining their usual exercise routine. This can create a vicious cycle: less muscle means lower metabolic rate, which contributes to weight gain.

7. Increased Body Fat (Especially Abdominal)

Low testosterone is associated with increased visceral fat, particularly around the abdomen. Elevated oestradiol (the primary oestrogen) often accompanies this — fat tissue contains aromatase, an enzyme that converts testosterone to oestrogen, further depleting testosterone levels.

8. Poor Sleep Quality

Testosterone and sleep have a bidirectional relationship. Low testosterone disrupts sleep architecture, and poor sleep further suppresses testosterone production. Men may experience insomnia, lighter sleep, or increased waking during the night.

9. Reduced Bone Density

Though less immediately noticeable, testosterone deficiency accelerates bone mineral loss. Over time, this increases fracture risk — a serious concern for men over 50.

Normal Testosterone Ranges by Age

Understanding reference ranges is essential for interpreting your results. The table below shows typical total testosterone ranges for men by age group, measured in nmol/L (the standard unit used in UK laboratories).

Age Group	Typical Total Testosterone (nmol/L)	Average (nmol/L)
18–29	12.0–31.0	17.5
30–39	10.0–28.0	16.5
40–49	8.5–25.5	15.5
50–59	7.5–24.0	14.5
60–69	6.5–23.0	13.5
70+	6.0–21.5	12.5

Important: A level within the “normal” range does not automatically mean everything is fine. BSSM guidelines highlight the grey zone between 8 and 12 nmol/L where men are symptomatic and may benefit from treatment. Similarly, a man whose testosterone was 25 nmol/L at age 25 may feel significantly different at 13 nmol/L in his 40s, even though both values fall within the reference range.

BSSM Clinical Thresholds

Level	Total Testosterone	Clinical Interpretation
Below 8 nmol/L	< 8 nmol/L	Likely testosterone deficiency — treatment usually recommended
8–12 nmol/L	8–12 nmol/L	Grey zone — check free testosterone; treatment may be warranted if symptomatic
Above 12 nmol/L	> 12 nmol/L	Generally sufficient — investigate other causes for symptoms

Total vs Free Testosterone: Why Both Matter

Most testosterone in the blood is bound to proteins — approximately 60–70% to sex hormone-binding globulin (SHBG) and 25–35% to albumin. Only 1–3% circulates as free testosterone, which is the biologically active form that enters cells and exerts effects.

This distinction matters clinically because SHBG levels vary considerably between individuals. Conditions that raise SHBG — ageing, liver disease, hyperthyroidism, and certain medications — can push total testosterone into the normal range while free testosterone is genuinely low.

BSSM guidelines recommend: If total testosterone falls between 8 and 12 nmol/L, free testosterone should always be measured. Free testosterone below 0.225 nmol/L supports a diagnosis of testosterone deficiency in symptomatic men.

This is precisely why a panel that includes both total testosterone, free testosterone, and SHBG is more informative than a single total testosterone reading.

When to Get Tested: Timing Matters

Testosterone follows a circadian rhythm, peaking in the early morning and declining throughout the day. Getting the timing wrong can produce a misleadingly low result. BSSM guidelines are specific:

• Time: Blood sample should be taken between 7 am and 11 am
• Fasting: Ideally fasting (or at least avoid a high-carb or high-fat meal beforehand) — eating can temporarily suppress testosterone by up to 30%
• Repeat testing: A single low reading is not diagnostic. BSSM requires at least two low readings, ideally 4 weeks apart
• Avoid acute illness: Do not test during periods of acute illness, high stress, or sleep deprivation — all temporarily lower testosterone

Home blood tests offer the advantage of sampling at the optimal time. With a finger-prick collection taken first thing in the morning before eating, you control the conditions in a way that is difficult in a GP surgery with limited early appointments.

What Causes Low Testosterone?

Understanding the underlying cause determines the right course of action. Causes are broadly divided into primary (testicular), secondary (pituitary/hypothalamic), and functional (lifestyle-driven).

Age-Related Decline

Testosterone declines by approximately 1–2% per year after age 30. By age 50, a man may have 20–40% less testosterone than in his twenties. However, age-related decline is not inevitable in all men — those who maintain a healthy weight, exercise regularly, and sleep well often preserve higher levels.

Obesity and Metabolic Syndrome

Excess body fat, particularly visceral fat, is one of the strongest modifiable predictors of low testosterone. Fat tissue contains aromatase, which converts testosterone to oestradiol. Higher oestradiol suppresses LH production from the pituitary, further reducing testosterone output. Insulin resistance (measurable via HbA1c) also directly impairs Leydig cell function.

Chronic Stress and Cortisol

Sustained high cortisol directly suppresses the hypothalamic-pituitary-gonadal (HPG) axis. Chronic stress from work, poor relationships, financial pressures, or overtraining can all contribute. Elevated CRP (a marker of systemic inflammation) often accompanies chronic stress and can further suppress testosterone production.

Sleep Deprivation

The majority of daily testosterone release occurs during sleep. Research shows that sleeping only 5 hours per night for one week can reduce testosterone levels by 10–15%. Quality matters as much as quantity — disrupted sleep and sleep apnoea are significant contributors.

Medications

Opioid painkillers, corticosteroids, some antidepressants, and 5-alpha reductase inhibitors (used for hair loss and prostate conditions) can all suppress testosterone. If you suspect a medication is contributing, discuss alternatives with your GP — do not stop prescribed medication without medical advice.

Other Medical Causes

Conditions affecting the testes directly (Klinefelter syndrome, undescended testes, mumps orchitis, testicular injury) or the pituitary gland (tumours, head injury, haemochromatosis) can cause testosterone deficiency. Measuring LH and FSH alongside testosterone helps distinguish between primary (testicular) and secondary (pituitary) causes.

What a Testosterone Blood Test Reveals

A single testosterone number tells you very little on its own. A comprehensive male hormone panel provides the context needed to understand why testosterone is low and what to do about it. Here is what each key biomarker adds:

Biomarker	What It Tells You
Total Testosterone	Overall testosterone production — the first-line screening marker
Free Testosterone	The biologically active fraction — what your body can actually use
SHBG	How much testosterone is bound and unavailable. High SHBG = less free testosterone even if total is normal
LH	Pituitary signal to the testes. High LH + low testosterone = primary (testicular) failure. Low LH + low testosterone = secondary (pituitary) cause
FSH	Supports LH interpretation and assesses fertility impact
Oestradiol	Testosterone-to-oestrogen conversion. Elevated oestradiol suggests excess aromatase activity (often linked to body fat)
DHT	The most potent androgen. Relevant to hair loss, prostate health, and overall androgen activity
TSH	Thyroid function screen. Hypothyroidism mimics many low testosterone symptoms (fatigue, weight gain, brain fog)
HbA1c	3-month average blood sugar. Insulin resistance is both a cause and consequence of low testosterone
Vitamin D	Deficiency is linked to lower testosterone levels and is extremely common in the UK (estimated 40% of adults)
Ferritin	Iron stores. Low ferritin causes fatigue and can mimic low testosterone symptoms. High ferritin may indicate haemochromatosis, a cause of secondary hypogonadism
CRP	Systemic inflammation marker. Chronic inflammation suppresses testosterone production

Low Testosterone in Women

While the focus of this article is on men, it is important to note that women also experience low testosterone — particularly during and after menopause. Symptoms include:

• Reduced libido and sexual satisfaction
• Persistent fatigue and low energy
• Low mood, anxiety, and irritability
• Loss of muscle tone and bone density
• Difficulty concentrating and memory lapses

NICE menopause guidelines recommend testosterone supplementation for women experiencing low sex drive when HRT alone is insufficient. In the UK, testosterone for women is prescribed “off-label” as the licence was withdrawn in 2012 for commercial rather than safety reasons.

Women experiencing these symptoms should discuss testing with their GP or consider a female hormone panel that includes testosterone, SHBG, and free testosterone.

Next Steps If Your Testosterone Is Low

If your blood test confirms low testosterone, the appropriate next steps depend on the cause and severity.

Lifestyle Interventions (First-Line for Functional Hypogonadism)

• Weight loss: Losing 10% of body weight can increase testosterone by 2–3 nmol/L. This is the single most effective intervention for overweight men with low testosterone.
• Resistance training: Compound exercises (squats, deadlifts, bench press) stimulate testosterone production. Aim for 3–4 sessions per week.
• Sleep optimisation: Prioritise 7–9 hours per night. Address snoring or suspected sleep apnoea — both significantly suppress testosterone.
• Stress management: Chronic cortisol elevation directly impairs testosterone production. Regular exercise, mindfulness, and work-life balance all help.
• Nutritional support: Ensure adequate vitamin D, zinc, and magnesium — all cofactors in testosterone synthesis.

Discuss with Your GP

Take your blood test results to your GP. A total testosterone below 12 nmol/L on two separate morning samples, combined with symptoms, meets BSSM criteria for further investigation. Your GP may refer you to an endocrinologist.

Testosterone Replacement Therapy (TRT)

Testosterone replacement therapy is recommended by BSSM for men with confirmed testosterone deficiency who do not respond to lifestyle interventions, or where levels are significantly low (below 8 nmol/L). TRT options in the UK include topical gels (Testogel, Tostran), injections (Sustanon, Nebido), and patches.

TRT is not appropriate for all men — it suppresses natural production and fertility, and requires ongoing monitoring of haematocrit, PSA, and liver function. Regular blood testing is essential both before starting and during treatment. Read our full guide to TRT and blood testing for more detail.

Frequently Asked Questions