Testosterone Explained: What It Does, Symptoms of Low Testosterone and How Testing Works

You open a testosterone report and see one number beside a wide range. It is easy to read that number as a verdict on energy, sex drive or ageing. In practice, it is only the start of the investigation. The result cannot explain a symptom, identify its cause or tell you whether treatment would help.

Testosterone levels shift during the day. Sleep, food, illness, medicines, body composition and the laboratory method can also change the reading. A low result on one morning may look different when it is checked again under the right conditions.

Testosterone is often reduced to sex drive and muscle, but its job is broader. In adult men it also supports sperm production, bone, red blood cells and several aspects of physical function. The testing guidance below is for adult men.

What Is Testosterone?

Testosterone is an androgen, a group of hormones involved in male sexual development and reproductive function. The testes make most of it, but production begins with a chain of signals from the brain.

• The hypothalamus releases gonadotropin-releasing hormone, or GnRH.

• GnRH prompts the pituitary gland to release luteinising hormone (LH) and follicle-stimulating hormone (FSH).

• LH tells cells in the testes to make testosterone. FSH works with testosterone to support sperm production.

• Rising testosterone sends feedback to the brain, which adjusts further production.

The combination of testosterone and LH can help locate a problem. Low testosterone with raised LH can point towards the testes. Low testosterone with low or unexpectedly normal LH can point towards the hypothalamus or pituitary, or towards temporary suppression caused by illness or medicine (Bhasin et al., 2018).

##

What Does Testosterone Do In Men?

During puberty, testosterone helps drive male sexual development. In adult men, its established roles include:

• sexual desire and normal erectile physiology

• sperm production and fertility

• maintenance of muscle mass and strength

• bone formation and bone density

• red blood cell production

• facial and body hair and other male secondary sexual characteristics

Mood, motivation and concentration are harder to pin on testosterone. Low mood, fatigue and poor concentration can occur with a low level, but they also have many other causes. It is better to speak with a doctor before making a snap assumption or starting hormones or supplements.

What Are The Symptoms Of Low Testosterone?

Low testosterone has no single tell-tale symptom. Sexual and reproductive changes are more closely associated with it than tiredness or low mood, but even the more specific symptoms can have other causes (Bhasin et al., 2018).

Sexual And Reproductive Symptoms

• a sustained fall in sexual desire

• fewer spontaneous or morning erections

• erectile difficulties

• reduced sperm production or fertility problems

Physical Signs And Longer-Term Effects

• loss of muscle mass or strength over time

• reduced body hair or smaller testes in prolonged or severe cases

• hot flushes in more marked deficiency

• low bone density or fractures in severe, long-standing deficiency

• unexplained anaemia

Less Specific Symptoms

• fatigue or reduced exercise tolerance

• low mood or irritability

• poor concentration

• weight change

A cluster of changes carries more information than one symptom. A persistent fall in sexual desire, fewer morning erections and repeatedly low testosterone is more suggestive than tiredness alone. Erectile difficulties still need a broad assessment because diabetes, vascular disease, smoking, medicines, sleep problems and psychological or relationship factors can all contribute.

What Can Cause Low Testosterone?

A lot of things can produce a low testosterone result. To start, it helps to understand hypogonadism. This means the testes are not making enough testosterone because of a problem in the testes themselves or in the hormonal signals that control them. Doctors diagnose it from compatible symptoms or signs together with consistently low results, then use other hormone tests to work out where the problem begins (Bhasin et al., 2018).

Primary hypogonadism begins in the testes. Testicular injury or infection, chemotherapy, radiotherapy and some genetic conditions can reduce testosterone production. LH often rises because the brain is sending a stronger signal but the testes cannot respond adequately.

Secondary hypogonadism begins in the hypothalamus or pituitary, the parts of the brain that send hormonal instructions to the testes. Pituitary disease, high prolactin, iron overload and medicines such as long-term opioids or glucocorticoids can interrupt those signals. LH may be low or unexpectedly normal.

Not every low result reflects lasting damage. Acute illness, severe calorie restriction, obesity, poorly controlled type 2 diabetes and recent withdrawal from anabolic steroids can suppress the hormonal system. Some of these effects may improve when the underlying condition changes, so a test taken during acute illness may not reflect a person’s usual level.

Do Testosterone Levels Fall With Age?

Older groups tend to have lower average testosterone than younger groups. Individual changes vary widely. Health, body composition, medicines and chronic illness can influence the result as much as age itself.

Figures such as a 1% fall per year describe an average across a population, not a personal countdown. Some men remain within their laboratory’s reference interval much later in life. Others develop symptoms or low results earlier because of an underlying condition.

Indian evidence also comes from selected populations. Studies have examined men over 40 attending a tertiary hospital and men receiving care for type 2 diabetes. They are useful for understanding those groups, but they do not establish the prevalence of testosterone deficiency among all Indian men. India also does not yet have a standardised national guideline for male hypogonadism (Kalra et al., 2023; Unnikrishnan et al., 2024; Yadav et al., 2019).

What Do Total, Free And Bioavailable Testosterone Mean?

Most testosterone in the bloodstream travels attached to proteins. A report may therefore describe total, free or bioavailable testosterone. They are related measurements, not interchangeable names for the same result.

Total Testosterone

Total testosterone includes protein-bound testosterone and the small amount that circulates unbound. It is usually the first blood test ordered when testosterone deficiency is suspected.

Free Testosterone

Free testosterone is the small fraction that is not attached to protein. It may help when total testosterone is close to the lower limit or when sex hormone-binding globulin is likely to be unusually high or low. Free testosterone can be calculated from total testosterone, SHBG and albumin, or measured by equilibrium dialysis in a specialist laboratory.

Sex Hormone-Binding Globulin

Sex hormone-binding globulin, or SHBG, is the main protein that carries testosterone. Low SHBG, which is common with obesity and insulin resistance, can make total testosterone appear low while free testosterone is less affected. High SHBG can produce the opposite pattern. Thyroid disorders, liver disease, age and several medicines can also alter SHBG.

Bioavailable Testosterone

Bioavailable testosterone combines free testosterone with the portion loosely attached to albumin. Some laboratories calculate or report it, but it is not the standard first test everywhere.

Which Testosterone Tests Are Used In India?

Blood is the standard sample. The first test usually measures total testosterone. If the result is borderline, or if SHBG is likely to be altered, a clinician may consider SHBG and calculate free testosterone. LH, FSH and prolactin are different hormones. They are follow-up tests that can help locate the cause after low testosterone has been confirmed.

Saliva and urine tests are not routinely used to diagnose testosterone deficiency in adult men. Clinical thresholds and assay performance are much better established for serum blood tests, which are also the basis of Indian expert recommendations and international guidance.

Laboratories do not all measure testosterone in the same way. Liquid chromatography-tandem mass spectrometry, or LC-MS/MS, is the most accurate method for measuring sex steroids. Automated immunoassays are more widely available and can be suitable for total testosterone. Direct immunoassays for free testosterone are not considered accurate enough for diagnosis. Results from different laboratories may therefore differ even when the samples were taken under similar conditions (Bhasin et al., 2018).

How Is Low Testosterone Diagnosed?

There is no age at which every man automatically needs a testosterone test. Testing is appropriate when symptoms, medical history, fertility concerns or physical findings raise a clinical question.

An assessment commonly includes:

• reviewing symptoms, medical history, medicines, fertility plans and relevant physical signs

• measuring total testosterone in a fasting morning blood sample, generally between 7 am and 10 am

• repeating the morning measurement on a separate day when the first result is low

• checking SHBG and free testosterone when total testosterone is borderline or SHBG may be altered

• using LH, FSH, prolactin or other tests to investigate the cause after low testosterone is confirmed (Bhasin et al., 2018)

Morning sampling reduces one avoidable source of variation. In one study, testosterone in men aged 30 to 40 was 20% to 25% lower at 4 pm than at 8 am. The daily swing was smaller in older men but could still change how a result was classified. Shift workers may need testing after an adequate sleep period rather than by the clock alone (Brambilla et al., 2009).

What Is A Normal Testosterone Range?

A laboratory reference interval shows the values found in a comparison population using a particular testing method. A diagnostic threshold is a decision aid that clinicians use alongside symptoms and other evidence. Neither number can define an individual’s health on its own.

Guidelines do not use exactly the same threshold. The Endocrine Society cites a harmonised lower limit of about 264 ng/dL in healthy, non-obese young men when the assay is accurate and standardised. The EAU uses 12 nmol/L, about 346 ng/dL, for late-onset hypogonadism when relevant symptoms are present. These figures come from different populations, assays and clinical purposes, so they should not be treated as interchangeable cut-offs (Bhasin et al., 2018; European Association of Urology, 2026).

FOXO uses normal and optimal as two different lenses. Normal means the result sits within the reporting laboratory’s reference interval. Optimal is a FOXO interpretation band used to ask whether the result deserves a closer look alongside age, symptoms, previous results and related markers. It is not a diagnosis, a treatment target or a reason to take testosterone. The laboratory method and the person’s clinical context still come first.

Why Is A Repeat Testosterone Test Important?

Testosterone changes during the day and from one day to another. Food, recent sleep, acute illness and laboratory methods can also shift the reading. A low first result is therefore usually checked with one more fasting morning sample on a different day. The second sample may be taken within days or later, depending on illness, recovery and the reason for testing.

An Indian multicentre study makes the process easier to picture. Men with type 2 diabetes who had screened positive for symptoms gave one fasting morning sample between study days 5 and 7. Those with a low result returned for one more fasting morning sample between days 9 and 14. They did not give blood every day. The proportion below 300 ng/dL fell from 18.4% at the first test to 8.6% on confirmation. The study does not represent all Indian men, but it shows how much the answer can change after one repeat test (Unnikrishnan et al., 2024).

Does A Low Result Mean You Need Testosterone Therapy?

No. Treatment is considered only after the result has been confirmed, symptoms have been assessed and the likely cause has been investigated. Testosterone therapy can help some men with established hypogonadism. It is not a general treatment for tiredness, low mood, erectile difficulties or ageing (Bhasin et al., 2018).

Trying to conceive changes the treatment discussion. Testosterone taken from outside the body tells the brain that enough hormone is already circulating. The brain then reduces LH and FSH, and the testes may make far less sperm. Men who want to preserve or restore fertility should discuss alternatives with an endocrinologist, urologist or fertility specialist. The Urological Society of India advises against using testosterone replacement to treat male infertility (Priyadarshi et al., 2023).

What Should You Do With A Testosterone Result?

First, check how the sample was taken: the time, whether you had eaten, recent illness, sleep schedule, unit and the laboratory’s reference interval. If the result is low or borderline, ask whether it should be repeated and whether SHBG or free testosterone would alter the interpretation.

At the appointment, mention symptoms, medicines, diabetes, thyroid function, recent weight change, sleep, alcohol use and fertility plans. A clinician can then judge whether the pattern suggests a persistent deficiency, temporary suppression or another explanation for the symptoms.

FOXO reads a testosterone result alongside related markers, symptoms, history and previous results. If you want help making sense of your own report, you can book an exploratory session with a FOXO Doctor or join<u> </u><u>FOXO Primer</u>. Primer brings these pieces together in a personalised playbook reviewed with a FOXO Doctor.

Frequently Asked Questions