You may be having a TRT blood test to confirm a low testosterone result or to monitor your health if you're taking TRT. At Leger, we require monitoring blood tests every six months once your treatment plan is established. These tests may include markers such as testosterone, SHBG, haematocrit, PSA, and oestradiol. But no single marker tells the whole story.

Your clinician looks at how the results fit together, when your blood was taken, how you’re feeling, and how things have changed over time.

This guide explains the key TRT blood tests, what they can reveal, and why context matters just as much as the numbers.

• Why do you need TRT blood tests?
• What does TRT blood work monitor?
• What if one of your TRT blood test results is outside the range?
• Why trends matter more than one blood test
• How often do you need TRT blood tests?

Why do you need TRT blood tests?

Testosterone replacement therapy (TRT) is used to restore testosterone levels in men with a confirmed deficiency, with the aim of improving related symptoms. Regular TRT blood tests help your clinician confirm that treatment is working as intended and remains safe.

Regular monitoring is used to:

• Check your testosterone response
• Ensure your treatment is safe and effective
• Monitor haematocrit and the wider blood count
• Assess prostate health where appropriate
• Investigate symptoms or possible side effects
• Compare new results with your previous blood tests
• Decide whether anything needs changing
• Make sure your blood test was taken at the right point in your treatment cycle

What does TRT blood work monitor?

TRT blood tests check several important biomarkers.

Testosterone

The aim of TRT is to restore testosterone to an appropriate physiological range rather than simply pushing the number as high as possible. 

A useful guide is:

• Total testosterone target of 15–30 nmol/L
• Free testosterone around 0.4–0.62 nmol/L 

Total testosterone

Total testosterone is all the testosterone circulating in your bloodstream, including testosterone bound to proteins and the small amount circulating freely.

Before TRT is started, testosterone blood test results help establish whether you have biochemical testosterone deficiency. Current BSSM guidance recommends measuring testosterone on at least two separate occasions before deciding whether treatment is necessary [1].

Once treatment has started, total testosterone levels help indicate whether your TRT is providing an appropriate level of hormone exposure. Monitoring it over time also helps your clinician assess whether your dose, preparation, and dosing schedule are working as intended. 

Free testosterone

Total testosterone tells you how much testosterone is circulating overall, while free testosterone gives a better indication of the amount that isn’t bound tightly to proteins. 

Only a small proportion of circulating testosterone is free and available. This becomes important when total testosterone and symptoms don’t seem to agree.

You can have a reasonable total testosterone result but relatively little free testosterone. Another man might have a lower total testosterone level, while the amount available to tissues remains adequate.

Free testosterone is often calculated using:

• Total testosterone
• SHBG
• Albumin

Read more about free testosterone vs total testosterone.

SHBG

Sex hormone-binding globulin (SHBG) is a protein that carries sex hormones through the blood. Its level strongly influences how a total testosterone result should be interpreted.

When SHBG is high, more testosterone is tightly bound. Total testosterone may look perfectly healthy, while the amount circulating freely is lower than expected.

With low SHBG, the reverse can happen. Total testosterone may appear relatively low even though free testosterone is more adequate.

That’s one reason two men with identical total testosterone results can feel very different.

SHBG can also be influenced by factors such as age, body composition, thyroid function, liver health, insulin resistance, and certain medications. Clinicians therefore use it as part of the wider picture rather than treating it as a target in itself.

Our guide to SHBG explains the relationship in more detail.

Albumin, total protein, and globulin

Albumin is another protein that carries hormones through the blood. It’s measured alongside total testosterone and SHBG to calculate free testosterone, which helps estimate how much testosterone is available to your tissues.

Total protein is the sum of albumin and globulin in your blood. Globulins are a broad group of proteins involved in transporting substances and supporting immune function.

Changes in albumin, total protein, or globulin can be linked to factors such as hydration, nutrition, inflammation, and liver or kidney health. These results aren’t used to adjust TRT on their own, but they can provide useful context when interpreting your wider blood panel.

Haematocrit

Haematocrit is one of the most important safety markers on a TRT blood test, indicating the percentage of your blood volume that is red blood cells.

Testosterone stimulates red blood cell production. For many men, that means haematocrit levels rise after TRT begins. A small rise isn’t automatically a problem, but it needs monitoring because some men develop a larger increase.

Other things can push haematocrit upwards, including:

• Dehydration
• Smoking
• Sleep apnoea
• Lung disease
• Living at altitude
• Problems with sample quality
• Other causes of increased red blood cell production

An elevated haematocrit can make blood more viscous. Clinicians become particularly concerned when the result reaches or exceeds 54%. Depending on the circumstances, that could involve adjusting the dose, changing your testosterone preparation, or temporarily interrupting treatment.

A result that has gradually climbed over several blood tests tells your clinician more than one unexpected reading.

Read our guide to high haematocrit on TRT for a closer look at what different results can mean.

Haemoglobin and red blood cells

Haematocrit usually appears as part of a full blood count, so you’ll probably also see haemoglobin and red blood cell measurements on your report.

They’re related, but they aren’t interchangeable.

• Haemoglobin is the oxygen-carrying protein inside red blood cells
• Red blood cell count records the number of red blood cells in a given volume of blood
• Haematocrit tells you the proportion of your blood volume occupied by those cells

Looking at the three together can help your clinician determine whether TRT is having a meaningful effect on red cell production and whether an unusual result needs to be repeated or investigated further.

Your full blood count may also include several red blood cell indices:

• MCV measures the average size of your red blood cells
• MCH measures the average amount of haemoglobin in each red blood cell
• MCHC measures the average concentration of haemoglobin within those cells
• RDW shows how much your red blood cells vary in size

These markers aren’t usually targeted for TRT treatment. However, they can help your clinician understand an abnormal haemoglobin, haematocrit, or red blood cell count and identify patterns that may need further investigation.

Platelets

Platelets are small blood cells that help your blood clot following an injury. Platelet count is included as part of the wider blood count rather than as a direct measure of your response to TRT.

An unusually high or low platelet count can have several possible causes, including illness, inflammation, medication, or an underlying blood disorder. Your clinician will interpret it alongside the rest of your blood count rather than in isolation.

White blood cells

White blood cells form part of your immune system. A comprehensive TRT panel may measure your total white cell count as well as different types of white blood cell:

• Neutrophils
• Lymphocytes
• Monocytes
• Eosinophils
• Basophils

Each has a slightly different role in protecting your body from infection, regulating inflammation, and responding to allergens or other foreign substances.

White blood cell results aren’t used to determine your TRT dose, but abnormal patterns can indicate an infection, inflammation, an allergic response, or another health issue that may affect how you feel or influence your other results.

Ferritin and iron stores

Ferritin is a protein that stores iron and provides an estimate of your body’s iron reserves. It can be particularly useful when interpreting tiredness or unusual haemoglobin and red blood cell results.

Low ferritin may indicate depleted iron stores. A raised result doesn’t always mean you have too much iron, as ferritin can also increase with inflammation, infection, or liver problems. Your clinician may recommend additional tests if your ferritin results don’t fit with the rest of your blood count.

Oestradiol

Oestradiol contributes to bone health, sexual function, and other physiological processes in men. A percentage of testosterone is converted into oestradiol by the enzyme aromatase. When testosterone rises during TRT, oestradiol levels may also increase.

The oestradiol result has to be interpreted alongside your testosterone exposure, symptoms, body composition, and treatment history.

A high result can become more relevant if you develop symptoms such as:

• Breast tenderness
• Gynaecomastia
• Fluid retention
• Changes in libido
• Sexual symptoms that haven’t improved as expected

Read more about oestradiol and high oestrogen on TRT.

PSA

Prostate-specific antigen (PSA) is a protein produced by prostate tissue and may be included in TRT blood work where prostate monitoring is clinically appropriate.

Testosterone treatment can cause an early physiological rise in PSA, which is another reason having a baseline result is useful. 

Levels can also be influenced by:

• Benign prostate enlargement
• Prostatitis or urinary infection
• Ejaculation
• Recent prostate procedures
• Age

A raised PSA doesn’t diagnose cancer, but an unexpected or persistent rise may need repeating, investigating, or referring to urology.

Read our guide to prostate health and TRT for more information.

LH and FSH

Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are particularly useful to measure before TRT starts.

They’re produced by the pituitary gland and help regulate testosterone production and sperm production in the testes.

If you have low testosterone, LH and FSH can help distinguish between different causes.

For example:

• Low testosterone with high LH can suggest the testes aren’t responding normally
• Low testosterone with low or inappropriately normal LH can point towards a problem higher up the hormonal pathway

When you begin TRT, the external testosterone can suppress the hypothalamic–pituitary–gonadal axis. As a result, LH and FSH usually fall during TRT. Once treatment is established, LH and FSH generally aren’t used to assess whether your TRT dose is correct in the same way as testosterone and haematocrit.

Prolactin

Prolactin is another pituitary hormone that may appear on a male hormone blood test.

It’s particularly useful before TRT, when low testosterone is accompanied by low libido, erectile problems, or evidence of secondary hypogonadism. Significantly elevated prolactin can sometimes indicate a pituitary problem and may warrant further investigation [1].

Once your TRT is established, prolactin doesn’t necessarily need to be checked at every review.

Liver markers

A comprehensive TRT blood test may include alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT).

• ALT is an enzyme found mainly in the liver and may rise when liver cells are irritated or damaged
• ALP is found in the liver, bile ducts, and bones, so an abnormal result needs to be interpreted alongside other markers
• GGT is associated with the liver and bile ducts and can help provide context for changes in ALP or other liver results

An abnormal liver marker doesn’t automatically mean TRT is responsible. Alcohol, medication, fatty liver disease, illness, and other health conditions may also affect these results.

Kidney function

Creatinine and estimated glomerular filtration rate (eGFR) provide information about how well your kidneys are filtering waste from your blood.

Creatinine is produced through normal muscle metabolism. Its level can be influenced by kidney function, muscle mass, hydration, recent exercise and creatine supplements.

eGFR is calculated partly from your creatinine result and estimates how effectively your kidneys are filtering your blood. Because creatinine can be affected by factors unrelated to kidney disease, your clinician will consider both results together and look at how they change over time.

Cholesterol

A full cholesterol profile provides more information than total cholesterol alone. It may include:

• Total cholesterol, which measures cholesterol overall
• LDL cholesterol, which can contribute to fatty deposits within the arteries when raised
• Non-HDL cholesterol, which includes LDL and other potentially harmful cholesterol particles
• HDL cholesterol, which helps transport cholesterol away from the bloodstream
• Total cholesterol-to-HDL ratio, which shows the balance between total and HDL cholesterol
• Triglycerides, which are fats used and stored by the body for energy

These results help your clinician assess your wider cardiovascular and metabolic health. They’re considered alongside factors such as blood pressure, body composition, smoking, diabetes, and family history rather than being interpreted as a direct measure of whether your TRT dose is correct.

HbA1c and blood glucose control

HbA1c reflects your average blood glucose level over approximately the previous two to three months. Unlike a standard glucose test, it doesn’t provide a snapshot of your blood sugar at the time your sample is taken.

It can help identify prediabetes or diabetes and monitor longer-term glucose control. This wider metabolic picture is relevant because insulin resistance, obesity, and type 2 diabetes commonly coexist with low testosterone.

HbA1c isn’t generally used to adjust your TRT dose directly, but an abnormal result may need to be discussed with your GP or another appropriate clinician.

Thyroid hormones

Some comprehensive TRT panels also measure thyroid-stimulating hormone (TSH), free thyroxine (free T4), and free triiodothyronine (free T3).

• TSH is produced by the pituitary gland and signals the thyroid to produce thyroid hormones
• Free T4 is the main circulating thyroid hormone and can be converted into the more active T3
• Free T3 measures the active thyroid hormone available to your tissues

Thyroid problems can cause tiredness, weight changes, low mood, and sexual symptoms that overlap with testosterone deficiency. Thyroid function can also influence SHBG, which may affect the interpretation of total and free testosterone results.

These markers help your clinician identify whether your symptoms or hormone results could have another explanation rather than showing how well TRT is working on their own.

What if one of your TRT blood test results is outside the range?

Reference ranges are designed to help interpret results in a population. They don’t automatically tell your clinician what needs treating, particularly when someone is taking prescribed testosterone.

Before making a change, your clinician may consider:

• How far outside the range is it?
• Has it changed since your last test?
• Was the blood sample taken at the correct time?
• Do you have any symptoms?
• Does another marker explain it?
• Could dehydration, illness, medication, or another factor have affected the result?
• Does the result actually represent a safety concern?

Why trends matter more than one blood test

TRT monitoring becomes much more useful once there are several results to compare.

Looking at results over time helps your clinician see whether something is:

• Stable
• Gradually changing
• Responding to a dose adjustment
• A one-off result
• Moving towards a level that needs action

Your TRT clinician isn't simply checking whether every result sits inside the laboratory reference range. They're looking at the relationship between your blood results, your treatment, your symptoms, and how those results have changed over time.

How often do you need TRT blood tests?

Blood testing is usually more frequent when you first start TRT or after your treatment changes, as your clinician needs to see how your testosterone responds, whether symptoms improve, and whether markers remain safe.

Once treatment is established and results are stable, monitoring usually becomes less frequent.

Not sure what your TRT blood results mean?

If you've had testosterone blood tests and aren't sure what they show, a TRT consultation gives you the opportunity to have your results reviewed in the context of your symptoms, medical history, and treatment options.

References

1. Hackett, G., Kirby, M., Rees, R.W., Jones, T.H., Muneer, A., Livingston, M., Ossei-Gerning, N., David, J., Foster, J., Kalra, P.A. and Ramachandran, S. (2023) The British Society for Sexual Medicine guidelines on male adult testosterone deficiency, with statements for practice, World Journal of Mens Health, 41(3), pp. 508–537. doi: 10.5534/wjmh.221027.