Blood test
Free testosterone test
Free testosterone test: what it measures, why a doctor orders it, how to prepare, and what a high or low result can mean - with private and NHS access routes in the UK.
Key facts
At a glance
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What it measures: the small unbound fraction of testosterone that is biologically active, usually calculated from total testosterone and SHBG.
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Why it is ordered: when the total testosterone is borderline or the binding protein SHBG is abnormal, to judge how much hormone is genuinely available to tissues.
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A fasting morning sample is usually advised, as levels are highest early in the day and are affected by food.
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Reference ranges: most UK laboratories report a calculated rather than directly measured value. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.
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A raised result in women supports clinically significant androgen excess. A low result with borderline total testosterone strengthens the case for true testosterone deficiency in men.
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Results are usually back within 24-48 hours when taken privately, and often the same day for urgent requests.
The full picture
What this test tells you, and how to get it
The free testosterone test measures the small unbound fraction of testosterone that is biologically active, usually calculated from total testosterone and SHBG. Doctors most often request it when the total testosterone is borderline or the binding protein SHBG is abnormal, to judge how much hormone is genuinely available to tissues. A fasting morning sample is usually advised, as levels are highest early in the day and are affected by food. Most UK laboratories report a calculated rather than directly measured value, and reference intervals genuinely differ between laboratories, so no single number should be treated as a universal cut-off - your result is always read against the range printed on your own report. Broadly, a raised result in women supports clinically significant androgen excess, while a low result with borderline total testosterone strengthens the case for true testosterone deficiency in men, and either finding is interpreted alongside your symptoms, medication and other results rather than in isolation. Results are usually back within 24-48 hours when taken privately, and often the same day for urgent requests.
In the UK there are two routes to this test. Your NHS GP can arrange it free of charge when it is clinically indicated, though getting the appointment, the blood draw and the follow-up discussion can add days to weeks depending on local demand. Privately, the free testosterone test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - as a calculated add-on to a testosterone and SHBG pair. A private result still deserves a clinician's interpretation: an isolated number without context is where most confusion about blood tests begins.
A quiet reminder
This guide is for information, not medical advice.
Your own clinician knows your history and can tell you which parts apply to you. Reference ranges vary between laboratories - always read your result against the interval printed on your own report. Next review of this page: 2027-09-27.
Frequently asked
Common questions about Free testosterone test.
Quick, plain-English answers to what people ask us most.
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What is a free testosterone test?
This test measures the small proportion of testosterone in your blood that isn't bound to proteins and is therefore biologically active. It gives a more direct picture of hormone availability than total testosterone alone, particularly when binding proteins are affected by other conditions.
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Why would a doctor order a free testosterone test?
It's used to investigate symptoms such as low libido, fatigue, reduced muscle mass, or erectile difficulties in men, and can help assess conditions like PCOS or excess hair growth in women. It's also useful when total testosterone results don't fully explain someone's symptoms.
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Do I need to prepare for it?
Testosterone levels vary through the day, so testing is usually done in the morning when levels are highest, and fasting isn't normally required. Let your doctor know about any medications or supplements you're taking, as some can affect results.
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What happens during the test?
It's a standard blood test taken from a vein in your arm, often alongside other hormone markers like SHBG, LH, and total testosterone to give a fuller picture.
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Does it hurt or have risks?
Only the usual minor discomfort of a blood draw, with no significant risks involved.
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How long do results take?
Results are typically available within a few days, and free testosterone calculations sometimes take slightly longer as they're derived from several related measurements.
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What do abnormal results mean, and what happens next?
Low free testosterone in men may be linked to fatigue, reduced libido, or other symptoms and may prompt discussion about lifestyle factors or treatment options. Raised levels in women can be linked to conditions like PCOS, and your doctor will interpret results alongside your symptoms and other hormone levels.
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How much does it cost privately, and is it available on the NHS?
Free testosterone testing is available on the NHS when clinically indicated, though it may not be automatically included in routine hormone panels. Private testing typically offers a fuller hormone panel with specialist review within days, and cost varies by provider.
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Is it accurate and reliable?
Free testosterone can be measured directly or calculated from total testosterone and binding proteins, and both approaches are considered reliable when done by an accredited lab. Timing of the sample and recent illness or medication can affect results, so context matters when interpreting them.
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How do I book it privately, and how quickly can I be seen?
You can book a private hormone blood test, usually with a morning appointment slot, and get specialist-reviewed results within a matter of days.