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Creatinine

Creatinine is a waste product of your muscles that your kidneys filter from the blood — a measure of kidney function.

What is Creatinine?

Creatinine is a breakdown product your muscles constantly produce. The kidneys filter it almost entirely from your blood. Because production per person is fairly constant and scales with muscle mass, the blood level reflects how well the kidneys are filtering. The key limitation: creatinine only rises measurably once kidney function has declined substantially. Muscle mass has a large effect — a muscular athlete will naturally run higher than someone with little muscle, without any kidney issue. Creatine supplementation and dehydration can also temporarily raise the value. Always read creatinine together with eGFR.

Why is Creatinine relevant?

Creatinine is the most widely used baseline marker for kidney function. When the kidneys filter less efficiently — from high blood pressure, diabetes, certain medications, or chronic kidney conditions — creatinine rises in the blood. A gradually rising creatinine across repeat measurements is an early signal to investigate further, even if the absolute value still sits within the reference range. For people supplementing with creatine: creatine use temporarily increases creatinine production and can raise the value without any kidney implication. Dehydration has the same effect. In both cases, eGFR is the more robust measure.

Creatinine high or low — what it means

Always read creatinine alongside eGFR, and factor in body composition, age, and hydration. A value just above the upper limit in a muscular, well-hydrated person is often normal for that individual. A value sitting within the range in an older person with little muscle mass can sometimes already signal a meaningful loss of kidney function. Wait at least 48 hours after heavy training or stopping creatine supplementation before testing, and make sure you are well hydrated. Trends across multiple measurements are more informative than one reading: a gradually rising creatinine with stable muscle mass and hydration is a clear signal to look more closely at kidney function.

Creatinine reference ranges

MenAdult; higher due to greater muscle mass. Some labs use 62-115 µmol/L.60-110 µmol/L
WomenAdult; lower due to less muscle mass. Some labs use 53-97 µmol/L.45-90 µmol/L

Cut-off values differ by laboratory and assay method. Creatinine is always interpreted together with eGFR; muscle mass, age and hydration affect the result. A value within the reference range does not rule out reduced kidney function in older people or those with low muscle mass.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

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Frequently asked questions

What is a normal creatinine level?

A normal blood creatinine sits roughly between 60 and 110 µmol/L in adult men and between 45 and 90 µmol/L in women. Men run naturally higher because of greater muscle mass. The exact limits vary by lab (some use, for example, 62-115 µmol/L for men and 53-97 µmol/L for women), so always check the reference interval on your own report. Always read creatinine together with eGFR.

What does a high creatinine mean?

A raised creatinine (above about 110 µmol/L in men or 90 µmol/L in women) can point to reduced kidney function: the kidneys are clearing this waste product less efficiently. But it isn't always a kidney problem — high muscle mass, creatine supplementation, a high protein intake, hard training or dehydration can temporarily lift the value. Creatinine also only rises clearly once kidney function has already dropped substantially (roughly 40-50%), which is why eGFR gives a more sensitive picture.

What does a low creatinine mean?

A creatinine below the reference range (under ~60 µmol/L in men or ~45 µmol/L in women) is usually not concerning and mostly reflects low muscle mass — for example in older people, a slight build, or after prolonged inactivity. Note: with low muscle mass creatinine can look 'normal' while kidney function is in fact reduced, so the calculated eGFR is the more reliable measure in that case.

When is an abnormal creatinine concerning?

Further investigation is sensible with a persistently raised creatinine or a falling eGFR, especially alongside risk factors such as high blood pressure, diabetes or kidney-stressing medication, or with symptoms like fatigue, fluid retention or reduced urination. A gradually rising creatinine across repeat measurements — with stable muscle mass and good hydration — is a clear signal to discuss with your doctor, even if the absolute value still sits within the range.

How do I measure my creatinine as reliably as possible?

A single value is only a snapshot. Wait at least 48 hours after heavy training or after stopping creatine supplementation before testing, and make sure you are well hydrated — training, creatine and dehydration can temporarily raise the value without anything being wrong with your kidneys. The trend across several measurements, with stable muscle mass and hydration, tells you more than one reading.

Related biomarkers

eGFR
eGFR is a calculated estimate of how fast your kidneys filter your blood, giving a general picture of kidney function.
AST
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Magnesium
Magnesium is a mineral involved in energy production, muscle function, and nerve signalling.
Vitamin D
Vitamin D is a vitamin your skin mainly makes under sunlight that supports your bones, muscles, and immune defence.

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