Ultimate Blood Test

What it is: The main male sex hormone, measured as the total amount circulating in your blood (both bound and unbound).

Why we test it: It's the starting point for diagnosing low testosterone and for checking your dose is keeping you in the optimal range once you're on TRT.

What it is: The small fraction of testosterone that isn't bound to proteins, so it's available to act on your body's testosterone receptors.

Why we test it: You can have a normal total testosterone but low free testosterone. Free testosterone often tracks symptoms more closely, so it gives a truer picture.

What it is: Sex hormone binding globulin, a protein made by the liver that binds tightly to testosterone and stops it being used by your tissues.

Why we test it: High SHBG can leave you with low free testosterone even when total testosterone looks fine. We need it to calculate free testosterone and to adjust your treatment.

What it is: The most common protein in your blood. It binds testosterone loosely, so some of that testosterone can still be released and used.

Why we test it: Albumin goes into the calculation of free testosterone. It's also a general marker of liver health and nutrition.

What it is: Luteinising hormone, the pituitary's signal telling the testes to make testosterone.

Why we test it: High LH with low testosterone points to a problem in the testes (primary hypogonadism). Low or normal LH points to the brain (secondary). That difference shapes your treatment options.

What it is: Follicle stimulating hormone, released by the pituitary gland in the brain. It drives sperm production in the testes.

Why we test it: Alongside LH, it shows whether low testosterone starts in the testes or the brain. It also matters for fertility, because TRT can suppress it.

What it is: A pituitary hormone best known for its role in milk production, which men also produce in small amounts.

Why we test it: Raised prolactin can suppress testosterone and lower libido. It can sometimes point to a pituitary issue that needs treating before TRT.

What it is: Your main stress hormone, made by the adrenal glands. It's highest in the morning.

Why we test it: Cortisol that stays high for a long time can suppress testosterone and cause fatigue and poor sleep. Very low levels can point to an adrenal problem that needs looking into.

What it is: DHEA-S, a hormone made by the adrenal glands that the body uses to build testosterone and oestrogen.

Why we test it: It shows how much your adrenal glands contribute to your hormones and helps explain energy, libido and how you're ageing hormonally.

What it is: Prostate specific antigen, a protein made by the prostate gland.

Why we test it: Testosterone can stimulate prostate tissue, so we check PSA before starting TRT and monitor it during treatment as a safety measure.

What it is: Thyroid stimulating hormone, the pituitary's signal to your thyroid to produce hormone.

Why we test it: It's the most sensitive first check of thyroid function. High TSH usually means an underactive thyroid, and low TSH an overactive one.

What it is: Free T3, the active form of thyroid hormone that sets your metabolic rate.

Why we test it: Low FT3 can cause fatigue, feeling cold and weight gain even when other thyroid markers look borderline.

What it is: Free T4, the main hormone the thyroid releases, which the body converts into active T3.

Why we test it: Read alongside TSH, it confirms whether your thyroid is under- or overactive.

What it is: Total T4, all the thyroxine in your blood, both bound to proteins and free.

Why we test it: It adds context to FT4 and helps interpret thyroid results when binding proteins are unusual.

What it is: Antibodies against thyroid peroxidase, an enzyme your thyroid needs to make hormone.

Why we test it: Raised levels are the hallmark of autoimmune thyroid disease (Hashimoto's) and can show up years before your thyroid hormones change.

What it is: Antibodies against thyroglobulin, a protein your thyroid uses to make and store its hormones.

Why we test it: Together with anti-TPO, it helps spot autoimmune thyroid disease early.

What it is: A measure of your average blood sugar over the past two to three months.

Why we test it: It screens for diabetes and prediabetes, which are closely linked to low testosterone. Improving blood sugar control is also one of the benefits we look for on TRT.

What it is: The amount of sugar in your blood at the moment the sample was taken.

Why we test it: It's a snapshot that complements HbA1c and can flag blood sugar problems that need following up.

What it is: A small protein that healthy kidneys filter out at a steady rate.

Why we test it: Unlike creatinine, it isn't affected by muscle mass, so it gives a more accurate kidney reading for muscular men or those taking creatine.

What it is: An electrolyte that controls fluid balance, blood pressure and nerve signals.

Why we test it: Abnormal levels can point to dehydration, kidney issues or hormone imbalances.

What it is: A waste product made when your body breaks down protein, cleared by the kidneys.

Why we test it: It helps assess kidney function and hydration. A high-protein diet can also raise it.

What it is: An electrolyte that works with sodium to keep your fluid and acid-base balance steady.

Why we test it: It adds context to your kidney and hydration picture.

What it is: Estimated glomerular filtration rate, a calculation of how much blood your kidneys filter each minute.

Why we test it: It's the standard way to grade kidney function and spot early decline.

What it is: A waste product from normal muscle activity, filtered out by the kidneys.

Why we test it: It's used to calculate eGFR. Note that muscular men and those taking creatine can have naturally higher levels.

What it is: The amount of iron circulating in your blood, which your body needs to make red blood cells.

Why we test it: Too little causes fatigue and breathlessness. Too much can damage organs over time.

What it is: Total iron binding capacity, how much iron your blood proteins could carry if fully loaded.

Why we test it: It helps tell iron deficiency apart from other causes of abnormal iron levels.

What it is: Unsaturated iron binding capacity, the spare room your blood proteins have to carry more iron.

Why we test it: Read with iron and TIBC, it completes the picture of your iron status.

What it is: Transferrin saturation, the percentage of your iron-carrying protein that is actually carrying iron.

Why we test it: Low saturation points to iron deficiency. High saturation can be an early sign of iron overload (haemochromatosis).

What it is: A protein that stores iron, so it reflects your body's iron reserves.

Why we test it: Low ferritin causes fatigue even before you become anaemic. High levels can point to inflammation or iron overload, which matters because TRT increases red blood cell production.

What it is: A hormone-like vitamin that your skin makes in sunlight. Many people in the UK are low, especially in winter.

Why we test it: It supports bone, muscle and immune health, and low levels are linked to lower testosterone.

What it is: A mineral involved in hundreds of processes, including muscle function, sleep and energy production.

Why we test it: Low magnesium can cause cramps, poor sleep and fatigue, and it plays a part in testosterone production.

What it is: A mineral essential for bones, muscle contraction and nerve signals.

Why we test it: Abnormal levels can point to problems with the parathyroid glands, vitamin D or the kidneys.

What it is: The number of red blood cells, which carry oxygen around your body.

Why we test it: TRT can raise red cell production, so we track it to keep your blood from becoming too thick.

What it is: The number of white blood cells, which are your immune system's defenders.

Why we test it: Abnormal counts can point to infection, inflammation or other conditions that need looking into.

What it is: Haemoglobin, the oxygen-carrying protein inside your red blood cells.

Why we test it: Low levels mean anaemia, which causes fatigue. High levels can be a side effect of TRT that needs managing.

What it is: Haematocrit, the percentage of your blood made up of red blood cells.

Why we test it: It's the key safety marker on TRT. If it rises too high your blood thickens and clot risk increases, so we monitor it closely and adjust your dose if needed.

What it is: Platelets, the small cells that help your blood clot.

Why we test it: Abnormal counts can affect bleeding or clotting risk and can point to other health issues.

What it is: Further measures such as red cell size (MCV) and the breakdown of white cell types.

Why we test it: They help pinpoint the cause of any abnormal result, for example whether anaemia comes from low iron or low B12.