Bodybuilder Blood Test: What to Monitor

Bodybuilding places extraordinary demands on the body. Heavy resistance training, high-protein diets, and — in some cases — performance-enhancing drugs (PEDs) all leave measurable traces in your blood. A routine blood test from your GP will often flag results as "abnormal" when they're actually expected for someone who trains intensely. The problem is knowing which abnormalities are benign adaptations and which are genuine warning signs.

Regular blood testing gives bodybuilders the data they need to train harder, recover faster, and protect long-term health. Here's exactly what to monitor and why each marker matters.

Testosterone, Free Testosterone and SHBG

Testosterone is the primary anabolic hormone driving muscle protein synthesis. For natural bodybuilders, tracking testosterone levels over time reveals whether training load, sleep, and nutrition are supporting hormonal health. The NHS reference range for total testosterone in men is 8.64–29 nmol/L, but optimal for muscle-building is generally considered above 15 nmol/L.

Total testosterone alone doesn't tell the full story. Sex hormone-binding globulin (SHBG) binds testosterone and makes it unavailable to tissues. If SHBG is elevated — common with ageing, low-carb diets, or hyperthyroidism — total testosterone may look fine while free testosterone is actually low. Free testosterone, the unbound fraction, is what drives anabolic activity in muscle tissue.

For those using exogenous testosterone or other androgens, monitoring is even more critical. Supraphysiological doses suppress natural production via the hypothalamic-pituitary-gonadal axis. LH and FSH will drop to near zero, confirming suppression. Post-cycle, these markers indicate whether natural production is recovering.

Creatine Kinase (CK): The Misunderstood Marker

Creatine kinase is released when muscle fibres are damaged. In sedentary individuals, the reference range is typically 30–200 U/L. In bodybuilders, CK is always elevated — values of 500–1,000 U/L after a heavy session are unremarkable, and readings above 2,000 U/L are not unusual following particularly intense eccentric training (think heavy negatives on bench press or walking lunges).

The concern is rhabdomyolysis — a potentially life-threatening condition where massive muscle breakdown floods the kidneys with myoglobin. CK levels above 10,000 U/L, combined with dark brown urine, severe muscle pain, and swelling, warrant immediate medical attention. The key distinction is context: CK of 1,500 U/L two days after a brutal leg session is adaptation. CK of 15,000 U/L with cola-coloured urine is an emergency.

If you're tracking CK over time, test at least 72 hours after your last heavy session to get a consistent baseline reading.

Liver Function: Why GGT Is the True Liver Marker for Gym-Goers

This is one of the most commonly misinterpreted results in bodybuilders. ALT and AST are routinely used as liver damage markers, but both enzymes are also present in skeletal muscle. Heavy resistance training causes ALT and AST elevations that have nothing to do with the liver. Studies have shown that intense exercise can raise ALT by 50–100% above baseline.

The marker that genuinely reflects liver health in bodybuilders is gamma-glutamyl transferase (GGT). GGT is liver-specific — it doesn't rise from muscle damage. If ALT and AST are elevated but GGT is normal, the elevation is almost certainly muscular. If GGT is also elevated, that's when liver investigation is warranted.

This distinction is particularly important for bodybuilders using oral anabolic steroids, which are 17-alpha-alkylated to survive first-pass metabolism and are genuinely hepatotoxic. Oral steroids like oxandrolone, stanozolol, and methandienone can cause cholestatic liver injury. Monitoring GGT alongside ALT/AST separates exercise-induced elevations from drug-induced liver stress.

Kidney Function: High-Protein Diets and Creatinine

Bodybuilders typically consume 2–3g of protein per kilogram of bodyweight daily — sometimes more during contest prep. This high protein intake naturally elevates blood urea and creatinine, both of which are waste products of protein metabolism and muscle turnover respectively.

Creatinine is particularly affected because it's a breakdown product of creatine phosphate in muscle. More muscle mass equals higher baseline creatinine. A 100kg bodybuilder may have a creatinine of 120 µmol/L (above the standard reference range of 59–104 µmol/L) with perfectly healthy kidneys.

The important marker is estimated glomerular filtration rate (eGFR), which adjusts for age and sex to estimate actual kidney filtering capacity. An eGFR above 90 mL/min indicates healthy kidney function regardless of what the raw creatinine number shows. If eGFR drops below 60, that warrants investigation — particularly in bodybuilders using NSAIDs regularly for joint pain, which can impair kidney function over time.

Urea is less specific but still worth tracking. Persistently elevated urea with declining eGFR is a combination that needs attention.

Lipid Panel: Cardiovascular Risk Assessment

The standard lipid panel measures total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. For natural bodybuilders, lipid profiles are generally favourable — regular exercise raises HDL and lowers triglycerides.

The picture changes dramatically with androgenic-anabolic steroid use. Exogenous androgens — particularly oral steroids — suppress HDL cholesterol by 40–70% while raising LDL. This creates a profoundly atherogenic lipid profile. A bodybuilder on a typical oral steroid cycle might have HDL of 0.4 mmol/L (healthy is above 1.0 mmol/L) with LDL above 4.0 mmol/L. Over years, this accelerates coronary artery disease. Multiple studies have found significantly increased coronary artery calcification in long-term anabolic steroid users compared to non-using bodybuilders.

Even natural bodybuilders should monitor lipids annually, particularly during extreme cutting phases where very high saturated fat intake or very low fat intake can temporarily alter the lipid profile.

HbA1c and Glucose: Insulin Sensitivity

Glycated haemoglobin (HbA1c) reflects average blood glucose over the preceding 8–12 weeks. The normal range is below 42 mmol/mol (6.0%). For most bodybuilders, resistance training improves insulin sensitivity, and HbA1c tends to be well-controlled.

However, insulin use in bodybuilding — used to drive glucose and amino acids into muscle cells — carries serious risks. Exogenous insulin can cause hypoglycaemia, and chronic use may eventually impair natural insulin sensitivity. Monitoring HbA1c and fasting glucose helps identify whether metabolic health is being maintained.

During aggressive bulking phases with very high carbohydrate intake (400–600g daily), fasting glucose can creep upward. Tracking HbA1c ensures this isn't becoming a chronic issue.

Full Blood Count: Haematocrit and Red Blood Cells

The full blood count (FBC) provides a comprehensive overview of red cells, white cells, and platelets. For bodybuilders, the critical value is haematocrit — the percentage of blood volume occupied by red blood cells.

Testosterone — whether endogenous or exogenous — stimulates erythropoiesis (red blood cell production) via erythropoietin. Natural bodybuilders with high-normal testosterone may have haematocrit at the upper end of normal (around 50%). Those using exogenous testosterone frequently see haematocrit rise above 52–54%, increasing blood viscosity and the risk of stroke, deep vein thrombosis, and pulmonary embolism.

Haematocrit above 54% is a commonly cited threshold for intervention. Regular blood donation is one strategy used to manage elevated haematocrit, though this should be discussed with a doctor. Monitoring haematocrit every 3–6 months is essential for anyone using testosterone replacement or supraphysiological doses.

How Often Should Bodybuilders Test?

For natural bodybuilders, a comprehensive panel once or twice per year is generally sufficient — ideally at the start of a training block and again before a competition prep or at the end of a bulk. For those using PEDs, testing every 3 months is a minimum, with additional tests during and after cycles.

Time your blood test to at least 48–72 hours after your last training session to reduce exercise-induced interference with CK, ALT, and AST. Fast for 10–12 hours beforehand if your panel includes glucose and lipids. Test testosterone in the morning before 10am, when levels are highest.

Which Blood Test Covers These Markers?

The Male Active Boost 36 biomarker test (£135) covers testosterone, SHBG, free testosterone calculation, liver function including GGT, kidney function, lipids, HbA1c, and full blood count — making it an excellent choice for natural bodybuilders who want a comprehensive panel without unnecessary extras.

For the most thorough assessment, including additional inflammatory markers and micronutrients, the Peak Insights 70 biomarker test (£185) provides the widest coverage available from a single blood draw. It's particularly useful for bodybuilders who want to monitor vitamin D, B12, folate, and iron status alongside the core markers discussed above.

The Bottom Line

Blood testing removes guesswork from bodybuilding. Rather than waiting for symptoms — fatigue, low libido, joint pain, dark urine — you can identify problems while they're still subclinical and reversible. The key is understanding which elevations are normal adaptations to training and which are genuine red flags. GGT over ALT for liver assessment, eGFR over raw creatinine for kidney health, and haematocrit for cardiovascular risk — these distinctions can make the difference between unnecessary worry and catching a real problem early.