Muscle metabolism waste cleared by the kidneys; basis for eGFR.
What it is
Serum creatinine in µmol/L. UK labs commonly calculate eGFR with CKD-EPI equations using age and sex (and sometimes ethnicity factors historically: follow current lab reporting).
Creatinine comes from creatine phosphate turnover in muscle. Production is relatively steady day to day for a given muscle mass. Serum creatinine in µmol/L underpins eGFR equations.
Why it matters
Rising creatinine or falling eGFR suggests reduced kidney function and needs clinical context. Muscle mass, cooked meat meals, creatine supplements, and some medicines affect creatinine. Hydration matters.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Creatinine production scales roughly with muscle mass; kidneys filter it at a relatively constant rate when healthy. Accumulation means filtration has fallen or production has surged.
Freely filtered at the glomerulus with little reabsorption, creatinine is a practical filtration marker. It does not measure tubular function or acute kidney injury as sensitively as newer markers in all settings.
For athletes
Muscular athletes can have higher baseline creatinine with a reassuring eGFR: bring sport context to your GP. NSAID overuse for sports pain plus dehydration is a kidney risk combo to avoid.
Large muscular athletes run higher creatinine; eGFR and urine tests add context. Avoid NSAID + dehydration stacks around races.
