Serum Creatinine Test

Creatinine is a waste product produced by normal muscle activity and cleared mainly through the kidneys. A serum creatinine result is often used to calculate estimated glomerular filtration rate (eGFR). Interpretation depends on age, body composition, clinical context and the laboratory method.

Serum creatinine is a waste product generated largely from normal muscle metabolism. The kidneys filter creatinine from the blood, so an increase can be a clue that filtration has fallen. However, creatinine is not a direct measurement of kidney function and is affected by muscle mass, body size, diet and some medicines.

For this reason laboratories often calculate an estimated glomerular filtration rate (eGFR) from the creatinine result. A clinician may also look at urine albumin, previous results and the trend over time rather than interpreting one creatinine value in isolation.

Creatinine is commonly included in broader kidney or metabolic panels rather than ordered alone. The laboratory may automatically calculate eGFR from the creatinine result, which usually adds more clinically useful context than creatinine by itself. If kidney disease is being assessed, urine albumin-to-creatinine ratio can provide different information about kidney damage and may be important even when eGFR is preserved. A clinician may also compare the result with potassium, urea, blood pressure, medication use and previous kidney results before deciding whether repeat testing or further assessment is needed.

Creatinine may be requested as part of kidney assessment, medicine monitoring, dehydration evaluation or before procedures that require knowledge of kidney function. It is commonly reported together with eGFR.

Serum creatinine is usually interpreted together with estimated glomerular filtration rate (eGFR), previous results and sometimes urine albumin testing. Higher creatinine can reflect reduced kidney filtration, but the concentration is also influenced by muscle mass, hydration, diet and some medicines. A person with low muscle mass can have a creatinine value that appears 'normal' even when kidney filtration is reduced.

Trends are often more informative than one isolated number. A change from a person's previous baseline can be clinically important even when the result remains inside a broad population interval, while a stable mildly different value may reflect individual physiology.

Creatinine is an indirect marker of filtration, not a complete kidney diagnosis. It can change for reasons unrelated to permanent kidney damage, and eGFR calculated from creatinine has its own limitations. Kidney assessment may also require urine albumin, urinalysis, blood pressure, imaging or repeat measurements depending on the reason for testing.

A venous blood sample is used. Fasting is generally not required for creatinine alone, although the laboratory may give specific advice about meat intake or combined tests. Share current medicines and supplements when results are being interpreted.