Kidney Function Blood Markers

Waste product from muscle metabolism. Elevated levels may indicate reduced kidney function.

PED: CRITICAL: Creatinine is directly proportional to muscle mass. Heavily muscled athletes will consistently show 'elevated' creatinine that is perfectly normal for their body composition. Creatine supplementation also elevates creatinine. Standard reference ranges are inappropriate for muscular individuals. Values up to 130 umol/L are common and normal. If creatinine is elevated, confirm kidney function with a Cystatin C test -- Cystatin C is not affected by muscle mass and gives a more accurate kidney assessment.

Calculated estimate of kidney filtration rate. Below 60 suggests kidney disease.

PED: Calculated from creatinine, so muscular athletes will show falsely low eGFR. An eGFR of 60-80 in a muscular individual is likely normal. Cystatin C-based eGFR is more accurate for athletes -- request this test to get a true picture of kidney function. If creatinine-based eGFR is low but Cystatin C is normal, kidney function is fine.

Waste product from protein metabolism. Elevated with high protein intake or kidney issues.

PED: High protein diets (common in bodybuilding) will elevate urea. This is expected and not concerning unless accompanied by elevated creatinine and low eGFR. Dehydration also elevates urea.

Product of purine metabolism. High levels can cause gout and kidney stones.

PED: High protein diets can elevate uric acid. AAS can affect uric acid levels. Adequate hydration important for clearance.

Small protein filtered by the kidneys. Unlike creatinine, Cystatin C is not affected by muscle mass, making it a more accurate kidney function marker for muscular individuals.

PED: CRITICAL: The gold-standard kidney marker for athletes with high muscle mass. Creatinine-based eGFR is unreliable in muscular individuals because creatinine scales with muscle mass, giving falsely 'elevated' readings and falsely low eGFR. Cystatin C-based eGFR removes this confounder entirely. If creatinine is elevated but Cystatin C is normal, kidney function is fine — the creatinine elevation is from muscle mass. Request this test whenever creatinine or eGFR results are ambiguous. Especially important when using nephrotoxic compounds (Trenbolone, high-dose orals) or chronic NSAID use.

Albumin in urine. Elevated levels (microalbuminuria) indicate early kidney damage, even before eGFR declines.

PED: Intense training can cause transient proteinuria — collect sample on a rest day for accurate baseline. High-dose AAS, especially trenbolone and oral 17-alpha alkylated compounds, may stress kidney filtration. Elevated urine albumin alongside high creatinine or low eGFR warrants further investigation. NSAIDs (commonly used for joint pain) can also impair renal function.

Creatinine concentration in urine. Used to calculate the albumin/creatinine ratio and assess specimen adequacy.

PED: Urine creatinine is higher in muscular individuals due to greater creatinine production from muscle mass. This is expected and not a concern — unlike serum creatinine, higher urine creatinine reflects normal excretion. A very low urine creatinine may indicate a dilute specimen (over-hydration before collection).

Ratio of urine albumin to creatinine. The primary screening marker for early kidney damage. Normal: <2.5 mg/mmol (males). Microalbuminuria: 2.5-25. Macroalbuminuria: >25.

PED: CRITICAL kidney health marker for PED users. ACR detects kidney damage earlier than eGFR changes. Trenbolone, high-dose orals (especially anadrol), and chronic NSAID use can impair renal filtration. Heavy training can cause transient elevation — always test on rest days. Serial monitoring is important: a single abnormal result should be confirmed with repeat testing. If persistently elevated alongside declining eGFR, nephrologist referral is warranted.

Calculated ratio of blood urea nitrogen to serum creatinine. Differentiates pre-renal (dehydration) from intrinsic renal causes of azotemia.

PED: CRITICAL CONFOUNDER FOR BODYBUILDERS: High muscle mass raises baseline creatinine (lowering the ratio) while high-protein diets elevate BUN (raising it). These opposing effects partially cancel out, making the ratio unreliable in isolation. Creatine supplementation further elevates creatinine. Dehydration during contest prep or weight cuts disproportionately raises BUN. Always interpret alongside individual BUN, creatinine, eGFR (preferably cystatin C-based), and hydration status. A 'normal' ratio does NOT rule out kidney issues in bodybuilders.