What blood tests are needed for TRT?
Reviewed by the My London Pharmacy clinical team, Yvonne Lim, Pharmacist Independent Prescriber
·27 August 2026
·6 min read
Quick answer
Before starting TRT, UK providers run a baseline panel covering testosterone (usually on two separate mornings), LH, FSH, full blood count, haematocrit, lipids, liver function and PSA where age-appropriate. Once treatment starts, testosterone and haematocrit are rechecked around 3 months in, then every 6 to 12 months, because TRT can raise red cell mass and needs monitoring for as long as you are on it. The same principle applies whether you are treated on the NHS or privately.
Testosterone replacement therapy (TRT) is a lifelong endocrine treatment, not a short course, so the blood tests around it are not a box-ticking formality. They confirm the diagnosis in the first place, set your safe starting point, and keep checking that treatment is doing what it should without causing harm elsewhere. This guide sets out exactly what is tested, when, and why, whichever route you take.
Why TRT relies on blood tests, not just symptoms
Low mood, fatigue, reduced libido and loss of muscle mass can all be symptoms of low testosterone, but they overlap heavily with poor sleep, stress, depression, thyroid problems and simply getting older. That overlap is exactly why a responsible clinician will not prescribe TRT on symptoms alone. A biochemical diagnosis, usually two early-morning total testosterone readings below the lab reference range, is what separates a genuine case of hypogonadism from symptoms with a different, non-hormonal cause.
The same logic carries through the rest of treatment. Testosterone affects your blood, prostate, liver and cardiovascular system, so ongoing bloods are how a clinician confirms those systems are staying in a safe range, not just how they confirm the medication is "working".
The baseline blood test panel
A typical UK baseline workup for TRT includes:
- Early-morning total testosterone, usually repeated on two separate days
- Free testosterone or sex hormone binding globulin (SHBG)
- Luteinising hormone (LH) and follicle stimulating hormone (FSH)
- Prolactin
- Full blood count, including haematocrit
- Lipid profile and liver function tests
- PSA (prostate-specific antigen), where age-appropriate
Some clinicians also add oestradiol, fasting glucose or HbA1c, particularly where symptoms or risk factors point towards a wider metabolic picture. Exactly which tests are included, and whether they are done as a venous draw or a home finger-prick kit, varies between providers, which is one of the things worth asking about before you start.
What each baseline test actually checks
Each test on that list is answering a specific question:
- Total and free testosterone. Confirms whether your level is genuinely low, not just at the bottom of a wide "normal" range.
- LH and FSH. These pituitary hormones help distinguish primary hypogonadism (a testicular problem) from secondary hypogonadism (a pituitary or hypothalamic problem), which can change the treatment approach.
- Prolactin. A raised result can point to a pituitary cause that needs its own investigation before TRT is considered.
- Full blood count and haematocrit. Sets your baseline red cell count before treatment, since TRT can raise haematocrit and thicken the blood.
- Lipids and liver function. A general safety baseline, checked periodically alongside everything else.
- PSA. A baseline prostate marker where age-appropriate, repeated during monitoring because testosterone can influence prostate tissue over time.
A clinician reads the panel as a whole, alongside your symptoms and medical history, rather than judging each result in isolation.
The follow-up testing schedule
Once treatment starts, most UK clinicians follow a broadly similar pattern: a check around 3 months after starting or after any dose change, another at 6 months, then every 6 to 12 months once your levels and symptoms are stable. The tests repeated at each round are usually testosterone level, haematocrit and PSA where age-appropriate, alongside a symptom review.
The early 3-month check matters more than it might seem. Haematocrit tends to rise fastest in the first few months of treatment, particularly with injectable formulations, so this is the point where a dose or interval adjustment is most likely to be needed.
What happens if a result comes back abnormal
An abnormal result is not automatically a reason to stop treatment, it is a reason to adjust it. If haematocrit rises above a safe threshold, a clinician will typically lower the dose, space out injections, or arrange venesection, a blood donation style procedure, to bring it back down before continuing. A raised PSA usually triggers a repeat test and, depending on the result, a referral for further prostate assessment, rather than an automatic diagnosis of anything serious. Your clinician should always explain what an out-of-range result means for you specifically, and what the next step is.
Are these tests available on the NHS?
Yes. If you are being investigated for suspected low testosterone through your GP, or already under an NHS endocrinology service, the same baseline and follow-up bloods described above are funded as part of that pathway. Where the NHS route differs is mainly speed and how testing is arranged: GP-ordered bloods and hospital laboratory turnaround can take longer to arrange and review than a private route with a home kit and a dedicated follow-up call, which is the main reason people choose to pay for testing rather than any difference in what is actually measured.
How much do the blood tests cost
Costs vary between providers, but as a general guide: a private baseline workup, including the consultation and full panel, commonly falls in the £150 to £400 region. Follow-up monitoring rounds typically cost £60 to £120 each if billed separately, adding roughly £200 to £500 across a full year on top of the medication itself. Some programmes bundle this monitoring into the ongoing monthly fee instead of billing it separately, which is one of the clearest ways to compare true cost between providers; our full TRT cost guide breaks this down route by route.
How fast do results come back
A home finger-prick or venous kit typically takes 3 to 5 working days to come back once your sample reaches the lab, and a venous draw at a clinic is usually similar. Once results are in, a clinician can normally review them and discuss next steps, including a prescription if appropriate, within the same appointment or a short follow-up call. NHS laboratory turnaround is broadly similar, though the time to actually get the sample taken and the results reviewed by a clinician can take longer depending on local waiting times.
Questions worth asking before you start
Before your first blood test, it is worth confirming:
- Exactly which tests are included in the baseline panel, and whether PSA is covered for your age group
- Whether testing is a home kit, a venous draw, or a choice of either
- How and when you will receive your results, and whether a clinician talks you through them
- What the follow-up testing schedule looks like once you are on treatment
- What happens, in practice, if your haematocrit or PSA comes back outside the expected range
A provider that can answer these clearly, before you have committed to anything, is a reasonable sign that monitoring is built into the programme rather than treated as an afterthought.
Frequently asked questions
Do I need blood tests before starting TRT?
Yes. TRT is only started once low testosterone is biochemically confirmed, usually on two separate morning samples, alongside a wider baseline panel covering hormone, blood count, prostate and liver markers. This applies whether you are treated on the NHS or privately.
How often will I need blood tests once I'm on TRT?
Most UK programmes test again around 3 months after starting or after a dose change, again at 6 months, then every 6 to 12 months once things are stable. Testosterone level, haematocrit and, where age-appropriate, PSA are checked at each round.
What happens if my haematocrit is too high on TRT?
TRT can thicken the blood by raising red cell mass. If haematocrit rises above a safe threshold, a clinician will typically reduce the dose, space out injections, or arrange venesection, a blood donation style procedure, to bring it back down, then re-test before continuing.
Are TRT blood tests available on the NHS?
Yes, if you are being investigated or treated for suspected hypogonadism through your GP or an NHS endocrinology service, the relevant baseline and follow-up bloods are funded as part of that pathway. Private testing is generally faster to arrange and interpret, which is the main reason people choose it.
How much do TRT blood tests cost privately?
A baseline workup, covering the consultation and full panel, commonly costs £150 to £400 privately in the UK. Follow-up monitoring rounds are usually £60 to £120 each if billed separately, though some programmes bundle monitoring into the ongoing monthly fee instead.