?Written by: London Blood Tests Editorial Team
Published: 31st of July 2026
Low energy, reduced sexual desire, erectile difficulties and loss of strength are sometimes associated with low testosterone. However, these symptoms are not specific to testosterone deficiency. Poor sleep, stress, depression, obesity, medication and several underlying health conditions can produce a similar pattern.
For adult men being investigated for possible testosterone deficiency, a testosterone blood test should generally be collected between 7:00 am and 11:00 am, preferably while fasting and when the person is otherwise well.
One low result is not normally enough to diagnose testosterone deficiency. The diagnosis requires compatible symptoms together with consistently low testosterone concentrations, usually confirmed through at least two properly timed morning samples.
Testosterone testing at a glance
- Arrange an initial diagnostic test between 7:00 am and 11:00 am.
- Use a fasting sample where possible.
- Do not test during an acute illness or infection.
- Do not diagnose testosterone deficiency from one result.
- Total testosterone is normally assessed first.
- SHBG and calculated free testosterone may help when total testosterone is borderline or SHBG is likely to be abnormal.
- London Blood Tests does not provide a standalone directly measured free testosterone test.
- Free Androgen Index should not be treated as equivalent to calculated free testosterone in men.
- LH, FSH and prolactin may be needed to investigate why testosterone is low.
- Initial assessment and treatment monitoring serve different purposes.
A joint UK position statement from the Society for Endocrinology and the Association for Laboratory Medicine states that non-fasting samples, samples collected after 11:00 am and results obtained during acute illness should not be used to diagnose male hypogonadism.
What does testosterone do?
Testosterone is an androgen hormone produced mainly by the testes in men. Smaller quantities are produced by the adrenal glands and, in women, the ovaries.
In adult men, testosterone contributes to:
- Sexual desire
- Erectile and reproductive function
- Sperm production
- Muscle mass and strength
- Bone health
- Red blood cell production
- Facial and body hair
- Mood and energy regulation
Testosterone concentrations may change with age, but symptoms should not automatically be attributed to an age-related hormonal decline.
The NHS describes “male menopause” as a potentially misleading expression because men do not usually experience the sudden hormonal transition associated with menopause in women. Symptoms such as low mood, reduced libido and fatigue may instead relate to stress, sleep, anxiety, depression, alcohol, smoking, obesity or another health condition.
When should testosterone be tested?
For adult men, the blood sample should normally be collected between 7:00 am and 11:00 am.
Testosterone follows a daily rhythm. Concentrations are generally highest earlier in the day and fall later, although the variation may be less pronounced in older men.
Correct timing is particularly important when:
- Testosterone deficiency is being investigated.
- A previous result was low or borderline.
- Results taken on different dates are being compared.
- A treatment decision may depend on the result.
- The patient is younger and daily variation is likely to be more pronounced.
The British Society for Sexual Medicine recommends measuring testosterone during the morning on at least two separate occasions, preferably several weeks apart and outside periods of acute illness.
What about night-shift workers?
A conventional morning appointment may not represent the biological morning of someone who regularly works overnight.
Shift work, disrupted sleep and irregular sleeping patterns can alter testosterone concentrations and complicate interpretation. Tell the test provider about your normal working and sleeping hours before booking.
A clinician may need to interpret the result in relation to your sleep pattern rather than relying only on the time shown on the clock.
Should you fast before a testosterone test?
A fasting morning sample is preferred for the initial investigation of possible testosterone deficiency.
Food intake can temporarily reduce measured testosterone, potentially creating a result that appears lower than it would under fasting conditions. Fasting also allows related metabolic markers to be collected under standardised conditions when they are required.
If fasting is requested:
- Avoid food for the instructed period, commonly 8–12 hours.
- Drink plain water.
- Avoid heavy alcohol intake beforehand.
- Avoid unusually strenuous exercise immediately before the appointment.
- Continue prescribed medicines unless your clinician advises otherwise.
- Tell the provider about supplements, hormones and non-prescribed products.
Do not stop prescribed medication solely to prepare for the test.
Avoid testing during an acute illness
Testosterone can temporarily fall during an infection, inflammatory illness, hospital admission or period of significant physical stress.
A low result obtained while you are acutely unwell may not represent your usual hormone status. Unless the test is urgently required for another clinical reason, it is generally preferable to wait until the illness has resolved.
Other factors that may temporarily affect testosterone include:
- Poor or insufficient sleep
- Significant calorie restriction
- Rapid weight loss
- Heavy alcohol consumption
- Intensive physical exertion
- Opioid medication
- Certain psychiatric or anticonvulsant medicines
- Anabolic steroid use
- Withdrawal from anabolic steroids or testosterone
Is one low testosterone result enough?
No. A diagnosis should not be made from one isolated measurement.
A proper diagnosis generally requires:
- Symptoms or signs compatible with testosterone deficiency; and
- Consistently low testosterone concentrations confirmed under appropriate collection conditions.
The Endocrine Society recommends repeating a morning fasting total testosterone measurement to confirm a suspected diagnosis. It also advises against routine population screening in men who do not have compatible symptoms or signs.
In a public statement issued on 16 July 2026, the Endocrine Society reiterated that symptoms alone are not diagnostic and that at least two early-morning fasting tests should form part of an accurate assessment.
How are testosterone results interpreted?
The result must be interpreted using the units and reference interval printed on the laboratory report.
In UK practice, assay methods and laboratory reference intervals vary. One universal cut-off should therefore not be applied without considering the method used, symptoms and wider clinical picture.
A joint UK position statement provides the following general action ranges for symptomatic adult men using properly collected morning fasting samples:
Total testosterone result | General interpretation |
Below 8 nmol/L on two occasions | Testosterone deficiency is more likely and the underlying cause should be investigated |
8–12 nmol/L | Borderline range requiring clinical correlation and sometimes further assessment |
Above 12 nmol/L | Testosterone deficiency is usually less likely |
These are clinical action points rather than universal laboratory reference intervals. A result must still be considered alongside symptoms, SHBG, medication, health conditions and the laboratory method.
Which London Blood Tests option should you choose?
London Blood Tests currently offers two relevant products with different purposes.
Test | What it assesses | Main purpose |
Testosterone Check | Total testosterone | Initial or standalone testosterone measurement |
Testosterone Monitoring | Total testosterone, SHBG, albumin and calculated androgen measures | Broader assessment of testosterone availability or monitoring |
Testosterone Check
The Testosterone Check measures total testosterone.
It may be suitable when:
- Testosterone is being measured for the first time.
- A healthcare professional has requested total testosterone.
- A previous result needs to be repeated.
- A baseline total testosterone measurement is required.
For the investigation of possible testosterone deficiency in an adult man, the sample should be fasting and collected before 11:00 am, even where more general product preparation instructions provide a wider appointment window.
Testosterone Monitoring
The Testosterone Monitoring panel includes:
- Total testosterone
- Sex hormone-binding globulin
- Albumin
- Calculated free testosterone
- Free Androgen Index
London Blood Tests does not currently offer a standalone directly measured free testosterone test. The calculated free testosterone result is estimated from total testosterone, SHBG and albumin. The product page lists five reported androgen-related markers and describes the panel as suitable for monitoring or a broader assessment.
The Testosterone Monitoring panel may provide useful context when:
- Total testosterone is borderline.
- SHBG may be unusually high or low.
- The total testosterone result does not correspond with the clinical picture.
- Prescribed testosterone treatment is being monitored.
However, it is not a complete investigation into the cause of low testosterone. If testosterone is repeatedly low, LH, FSH, prolactin and further clinical assessment may still be required.
Total testosterone and calculated free testosterone
Most testosterone in the bloodstream is attached to proteins.
Circulating testosterone consists of:
- Testosterone strongly bound to SHBG
- Testosterone more loosely bound to albumin
- A small unbound fraction
Total testosterone
Total testosterone measures testosterone across all three circulating forms. It is normally the first biochemical marker used when investigating possible testosterone deficiency.
The meaning of a total testosterone result depends on:
- Collection time
- Fasting status
- Symptoms
- SHBG concentration
- Current medication
- Recent illness
- General health
- Previous results
A result should not be compared with a random range found online. Use the reference interval and units shown on the laboratory report.
Calculated free testosterone
Direct free testosterone measurement is technically demanding. Equilibrium dialysis followed by mass spectrometry is regarded as a reference method, but it is not routinely available in UK clinical practice.
Other direct laboratory methods may be inaccurate. For this reason, testosterone availability is often estimated using a validated calculation based on:
- Total testosterone
- SHBG
- Albumin
Calculated free testosterone can be useful when total testosterone is borderline or SHBG is outside its reference interval.
When SHBG is within its expected range, calculated free testosterone may add little diagnostic information beyond total testosterone. When SHBG is high, it may help identify reduced testosterone availability despite a satisfactory total result. When SHBG is low, it may help show that testosterone availability is less reduced than the total result suggests.
What is the Free Androgen Index?
The Free Androgen Index, or FAI, is calculated from total testosterone and SHBG:
Total testosterone ÷ SHBG × 100
It is an index rather than a direct measurement of unbound testosterone.
Although FAI may appear on laboratory reports and is commonly used when assessing androgen excess in women, it should not be treated as equivalent to a validated calculated free testosterone result in men.
Research has shown that FAI can be strongly distorted when SHBG is unusually high or low. A mass-action calculation that incorporates total testosterone, SHBG and albumin is generally more appropriate for estimating free testosterone in men.
The FAI value reported by the Testosterone Monitoring panel should therefore be reviewed in context and should not be used alone to diagnose male testosterone deficiency.
Why is SHBG important?
Sex hormone-binding globulin, or SHBG, is a protein produced mainly by the liver. It binds strongly to testosterone and affects the amount available to tissues.
High SHBG
When SHBG is unusually high, total testosterone may appear satisfactory while calculated free testosterone is lower.
High SHBG may be associated with:
- Increasing age
- An overactive thyroid
- Some liver conditions
- Oestrogen exposure
- Certain medicines
Low SHBG
When SHBG is low, total testosterone may appear reduced while calculated free testosterone remains less affected.
Low SHBG may be associated with:
- Obesity
- Insulin resistance
- Type 2 diabetes
- An underactive thyroid
- Some metabolic conditions
UK laboratory guidance recommends checking SHBG when total testosterone is borderline or a condition likely to alter SHBG is present.
Why is albumin included?
Albumin is a protein produced by the liver. Testosterone binds to albumin less strongly than it binds to SHBG.
The albumin measurement can be included with total testosterone and SHBG when calculating estimated free testosterone.
Albumin also provides broader information about liver protein production, kidney protein loss, inflammation, hydration and nutrition. However, albumin alone cannot diagnose testosterone deficiency.
Which tests may help explain a low result?
A low testosterone measurement describes a biochemical finding. It does not explain why the concentration is low.
Further tests may help distinguish reduced testicular production from reduced signalling by the pituitary gland or hypothalamus.
Luteinising hormone
Luteinising hormone, or LH, is produced by the pituitary gland and stimulates the testes to produce testosterone.
Broadly:
- Low testosterone with raised LH may suggest a primary testicular problem.
- Low testosterone with low or inappropriately normal LH may suggest reduced pituitary or hypothalamic signalling.
The Endocrine Society recommends measuring LH and FSH to distinguish primary testicular hypogonadism from secondary pituitary–hypothalamic hypogonadism.
Follicle-stimulating hormone
Follicle-stimulating hormone, or FSH, contributes to testicular function and sperm production.
FSH may be particularly relevant where there are:
- Fertility concerns
- Abnormal semen analysis results
- Suspected testicular dysfunction
- A history of testicular injury or surgery
- A need to distinguish primary from secondary hypogonadism
A testosterone result is not a replacement for semen analysis when fertility is the main concern.
Prolactin
Prolactin is produced by the pituitary gland. Raised prolactin can interfere with reproductive hormone signalling and contribute to lower testosterone.
Prolactin may be considered where low testosterone occurs with:
- Low or inappropriately normal LH and FSH
- Reduced libido
- Erectile dysfunction
- Infertility
- Breast discharge
- Headaches
- Visual symptoms
- Suspected pituitary disease
Stress, medication and collection conditions can also raise prolactin. One abnormal result does not automatically indicate a pituitary tumour.
Oestradiol
An oestradiol blood test is not required for every man undergoing testosterone testing.
It may be considered where there is:
- Breast enlargement or tenderness
- Significant obesity
- Liver disease
- Prescribed testosterone use
- A specific concern about excess oestrogen activity
Oestradiol should be included only where it addresses a defined clinical question.
Other conditions can cause similar symptoms
Low energy, low mood, reduced libido and changes in body composition are not always caused by testosterone deficiency.
Assessment | Why it may be relevant |
HbA1c | Investigates longer-term blood glucose and possible diabetes |
Thyroid function | Thyroid dysfunction can affect energy, weight, sexual function and SHBG |
Full blood count | May identify anaemia and provides a baseline before some treatments |
Liver function | Liver health can influence SHBG and hormone metabolism |
Medication review | Opioids, steroids and other medicines can suppress testosterone |
Sleep assessment | Poor sleep and sleep apnoea may affect symptoms and hormone concentrations |
Mental health assessment | Anxiety and depression can affect energy, motivation and sexual function |
An HbA1c blood test may be relevant where obesity, insulin resistance, diabetes symptoms or metabolic risk are present.
Liver function tests may be useful where alcohol intake, medication, liver disease or abnormal SHBG is part of the clinical picture.
Testing should be selected according to symptoms and risk factors rather than ordering every possible marker.
Initial testing and treatment monitoring are different
An initial testosterone blood test asks whether testosterone is consistently low under appropriate collection conditions.
Treatment monitoring asks different questions:
- Is the prescribed treatment producing the intended testosterone level?
- Was the sample timed correctly in relation to the latest dose?
- Are symptoms improving?
- Is haemoglobin or haematocrit rising?
- Are there adverse effects?
- Is prostate assessment required?
- Does the dose or formulation need clinical review?
Sample timing depends on whether treatment is given as a gel, short-acting injection, long-acting injection or another formulation. People receiving prescribed testosterone should follow the timing and monitoring plan supplied by their clinician.
Do not start, stop or change testosterone treatment using a private laboratory result alone.
Testosterone treatment and fertility
External testosterone can suppress LH and FSH, reducing or stopping sperm production.
This is particularly important for younger men and anyone who may wish to conceive. The Endocrine Society recommends against beginning testosterone therapy in men who are planning fertility in the near term.
Before beginning treatment, tell the prescribing clinician about:
- Current fertility plans
- Possible future fertility
- Previous semen analysis results
- Testicular injury or surgery
- Previous anabolic steroid use
A fertility specialist or endocrinologist may need to consider alternatives that do not suppress sperm production in the same way.
Can women have a testosterone test?
Women also produce testosterone, but at much lower concentrations. Testing is used for different clinical questions and requires different reference intervals.
A testosterone test may be considered when investigating:
- Excess facial or body hair
- Acne
- Irregular periods
- Polycystic ovary syndrome
- Suspected androgen excess
- Certain ovarian or adrenal conditions
- Prescribed testosterone use during menopause care
The adult male morning-testing pathway and male diagnostic thresholds should not automatically be applied to women.
Women receiving prescribed testosterone should follow the monitoring instructions provided by their menopause clinician.
How to prepare for your appointment
Before attending a male hormone blood test, consider the following:
- Book before 11:00 am if possible testosterone deficiency is being investigated.
- Confirm whether fasting is required.
- Avoid testing while acutely unwell.
- Bring previous testosterone results.
- Note the time and fasting status of previous samples.
- Mention night-shift work or an irregular sleep pattern.
- Disclose prescribed testosterone, anabolic steroids or other hormones.
- Tell the provider when your latest treatment dose was taken.
- Mention opioid use and other regular medication.
- Explain any fertility plans.
- Report headaches, visual changes or breast discharge.
- Mention previous testicular injury, surgery or pituitary disease.
This information helps determine whether total testosterone alone is appropriate or whether SHBG, albumin, LH, FSH or prolactin may add useful information.
Where can you arrange a testosterone blood test in London?
Private testosterone testing is available through London Blood Tests partner clinics in:
- Knightsbridge: Astrum Medical, 43 Cheval Place, SW7 1EW
- Holborn: GB MedLabs, 1 Portpool Lane, EC1N 7UU
- Paddington: Dr Ducu Clinics, 199 Gloucester Terrace, W2 6LD
- Gants Hill: Olive Health, 23A Seven Ways Parade, IG2 6JX
Home and hotel blood collection can also be arranged. London Blood Tests lists its telephone number as 0203 488 0809. Appointment availability, collection fees and current turnaround times should be checked when booking.
Patients comparing a testosterone test London service should check exactly which biomarkers are included. Some tests measure total testosterone only, while others add SHBG and albumin for a calculated assessment.
For an initial testosterone blood test London appointment, a total testosterone measurement may be an appropriate starting point. A broader panel may provide additional context where total testosterone is borderline, SHBG may be abnormal or treatment is already being monitored.
Neither product should be treated as a diagnosis without appropriate clinical interpretation.
What should you do with your results?
A healthcare professional may consider:
- Symptoms and clinical signs
- At least two morning fasting testosterone results
- SHBG and calculated free testosterone where appropriate
- LH and FSH
- Prolactin
- Medication and supplement use
- Sleep and shift-work patterns
- Body weight and metabolic health
- Fertility plans
- Previous testosterone or anabolic steroid use
Seek medical advice if:
- Testosterone is repeatedly below the laboratory range.
- Sexual symptoms are persistent.
- You have fertility concerns.
- You are using or considering testosterone treatment.
- LH, FSH or prolactin is abnormal.
- You experience headaches, visual changes or breast discharge.
- Symptoms are severe or remain unexplained.
Frequently asked questions
What time should a testosterone blood test be taken?
For adult men being investigated for testosterone deficiency, the sample should usually be collected between 7:00 am and 11:00 am.
Do I need to fast?
A fasting sample is preferred for the initial diagnostic assessment. Follow the preparation instructions supplied for the exact test you book.
Is one low testosterone result enough?
No. A low or borderline result should normally be confirmed through a second fasting morning sample and interpreted alongside compatible symptoms.
Does London Blood Tests offer free testosterone?
London Blood Tests does not offer a standalone directly measured free testosterone test. The Testosterone Monitoring panel uses total testosterone, SHBG and albumin to report a calculated free testosterone value.
Is Free Androgen Index the same as calculated free testosterone?
No. FAI is a ratio of total testosterone to SHBG. Calculated free testosterone uses a more detailed equation that incorporates total testosterone, SHBG and albumin. FAI should not be used alone to diagnose testosterone deficiency in men.
When is SHBG useful?
SHBG is particularly useful when total testosterone is borderline or a medical condition may be causing SHBG to be unusually high or low.
Why are LH and FSH tested?
LH and FSH can help distinguish reduced testicular hormone production from reduced signalling by the pituitary gland or hypothalamus.
Can testosterone treatment affect fertility?
Yes. External testosterone can suppress sperm production. Anyone wishing to conceive should discuss fertility before beginning treatment.
Can women take a testosterone blood test?
Yes, but the reasons for testing, collection considerations and reference intervals differ from those used for adult men.
Book a private testosterone blood test in London
London Blood Tests provides total testosterone testing and broader testosterone monitoring through London clinics and home or hotel appointments.
The Testosterone Check may be suitable for an initial total testosterone measurement. The Testosterone Monitoring panel adds SHBG and albumin, allowing calculated free testosterone to be reported where a broader assessment is appropriate.
The broader panel also reports FAI, but this should not be treated as equivalent to calculated free testosterone or used alone to diagnose testosterone deficiency in men.
The most appropriate test is not necessarily the one with the greatest number of biomarkers. It is the test that answers the clinical question, is collected under suitable conditions and is interpreted alongside symptoms and medical history.
References
- Society for Endocrinology and Association for Laboratory Medicine: Standardising the Biochemical Confirmation of Adult Male Hypogonadism
- British Society for Sexual Medicine: Guidelines on Male Adult Testosterone Deficiency
- Endocrine Society: Testosterone Therapy for Hypogonadism Guideline
- Endocrine Society: Statement on Testosterone Replacement Therapy, 16 July 2026
- NHS: The “Male Menopause”
- London Blood Tests: Testosterone Check
- London Blood Tests: Testosterone Monitoring
Medical disclaimer: This article provides general information and does not replace individual medical advice, diagnosis or treatment. Speak to a qualified healthcare professional about persistent symptoms, low testosterone results, fertility concerns or testosterone treatment.