Creatinine

Women: 45 to 84 umol/L · Men: 59 to 104 umol/L

UK labs print separate ranges for women and men because muscle mass differs; the range is also lower in pregnancy and in older or frailer people.

Creatinine is a waste product made by the muscles at a fairly steady rate every day. The kidneys remove it from the blood, so the amount left in the blood is a guide to how well the kidneys are filtering. The test measures the level in a blood sample.

It is the most widely used blood test of kidney function and is part of the routine 'U&E' or 'renal profile'. Doctors also use it to calculate the eGFR and to keep an eye on the kidneys when certain medicines are being taken.

• Reduced kidney filtering, whether short-term or long-term
• Dehydration on the day of the test
• Large muscle mass or a recent heavy workout
• Eating a large amount of cooked meat before the test
• Some medicines, including certain antibiotics and stomach-acid tablets
• Creatine supplements used by gym-goers

• Low muscle mass, including in older age and in long illness
• Pregnancy, because the blood volume expands
• Some liver conditions
• A very low-protein diet

• A single value moves with hydration, exercise and what was eaten the day before
• Muscular people sit higher in the general population and slim or older people sit lower, without any change in the kidneys
• Different laboratory methods give slightly different numbers

No fasting needed, but avoiding a heavy meat meal and hard exercise the day before gives a steadier reading. The trend over months matters more than any single value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.