Creatinine and estimated glomerular filtration rate (eGFR) !

Creatinine comes from muscle and is filtered by the kidney; it is used to estimate how much the glomeruli filter.

Updated 2026-11-01

Key facts

Creatinine forms non-enzymatically and at a steady rate from muscle creatine and phosphocreatine.
It is freely filtered and slightly secreted by the tubule; its level rises when glomerular filtration falls.
The relation is not linear: early on, nearly half of filtration can be lost with little change in creatinine.
eGFR is calculated with equations (race-free CKD-EPI 2021) from creatinine, age and sex; cystatin C improves the estimate.
Chronic kidney disease (KDIGO): low GFR (< 60 mL/min/1.73 m²) or a marker of damage (albuminuria) for more than 3 months; normal creatinine values vary by laboratory.

What it measures: serum creatinine concentration (Jaffe or enzymatic method). eGFR is not measured: it is calculated.
Where it comes from: about 1–2 % of muscle creatine becomes creatinine each day; so it depends on muscle mass and on meat eaten.
Why it rises: acute kidney injury (prerenal, renal, postrenal), chronic kidney disease, rhabdomyolysis, recent cooked meat, creatine supplements.
Pitfalls: people with little muscle (older adults, amputees, people with cirrhosis or malnutrition) have a 'normal' creatinine with low filtration; trimethoprim and cimetidine block tubular secretion and raise creatinine without lowering filtration; ketones and some cephalosporins interfere with the Jaffe method.
eGFR equations do not apply when function is changing fast (acute kidney injury): then the change in creatinine and urine output is followed.
24-hour urine creatinine clearance overestimates filtration because of tubular secretion and depends on a complete collection.

Acute kidney injury (KDIGO) is defined by a rise in creatinine within 48 h or 7 days, or by low urine output for hours.
eGFR guides dose adjustment of renally cleared drugs (metformin, aminoglycosides, direct anticoagulants).
Diabetes and hypertension are the leading causes of chronic kidney disease in Colombia and worldwide.

Think of the answer, then tap the question to see it.

Where does serum creatinine come from?

From the spontaneous, steady conversion of muscle creatine and phosphocreatine; so it depends on muscle mass.

Why does a normal creatinine not rule out low kidney function in a frail older adult?

Low muscle mass makes little creatinine, so filtration can be reduced with an apparently normal value.

What defines chronic kidney disease by KDIGO?

A GFR below 60 mL/min/1.73 m² or a marker of kidney damage (such as albuminuria) lasting more than 3 months.

Why can trimethoprim raise creatinine without harming the kidney?

It blocks tubular secretion of creatinine, so the level rises although glomerular filtration does not change.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Creatinine Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Estimated Glomerular Filtration Rate (eGFR) and GFR Tests: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Creatinine blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Kidney Tests: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.