Creatinine blood test: normal range explained

A creatinine test measures the level of creatinine in your blood. Creatinine is a normal waste product made when you use your muscles and some muscle tissue breaks down; it comes from creatine, which muscles use for energy. Healthy kidneys remove it from the blood into urine, so the blood level reflects how well the kidneys are filtering.

Doctors order creatinine to check kidney health, often as part of a routine check-up or a kidney function test, and to follow people with known kidney disease, diabetes, high blood pressure or heart disease. On its own it is not the best measure: MedlinePlus says creatinine is usually fed into a formula with your age and sex to estimate eGFR, which is a more accurate picture. It is also read beside BUN or urea from the same sample.

Creatinine depends on your muscle mass and what you did before the test, not only on your kidneys.

• Muscle mass matters most: men usually have higher levels than women, and athletes and people who do strength training sit at the higher end of the range.
• Eating meat shortly before the sample can raise creatinine temporarily; Lab Tests Online UK says by 10 to 30%, and suggests avoiding meat for 12 hours before the test.
• Creatine supplements and hard exercise in the day before the test can raise the level.
• Some medicines, such as cimetidine, trimethoprim and some HIV medicines, raise creatinine without changing kidney function. Tell your doctor what you take and do not stop a medicine on your own.
• Dehydration pushes the level up, while pregnancy, a vegetarian diet, low muscle mass and severe liver disease pull it down.
• Levels are lower in children and in older people with less muscle, which your doctor considers.