The creatinine blood test measures the level of creatinine in the blood. The result of this blood test is useful, as it is an important marker of how well the kidneys are working.

Creatinine is the waste product of creatine, which the muscles use to make energy. Typically, creatinine travels in the blood to the kidneys, where it leaves the body in the urine. High levels in the blood might indicate that the kidneys are not working correctly.

The creatinine blood test helps doctors diagnose kidney disease. A poorly functioning kidney cannot filter creatinine as well as it usually does, which causes levels in the blood to rise.

In this article, we discuss normal creatinine levels, what affects these levels, and what the results mean.

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The kidneys are responsible for keeping the level of creatinine in the blood within a normal range.

Medical professionals define the typical reference ranges for serum creatinine in micromoles per liter (μmol/L) and milligrams per deciliter (mg/dL).

Below are average reference ranges for adult males and females.

Average creatinine levels (μmol/L)Average creatinine levels (mg/dL)
Adult male60–1100.7–1.2
Adult female45–900.5–1.0

Some of the causes of high creatinine levels are:

Chronic kidney disease

When kidneys are damaged, they have trouble removing creatinine from the blood, and levels rise.

Doctors use the creatinine blood test result to calculate glomerular filtration rate (GFR), which is a more specific measure that can indicate chronic kidney disease.

Doctors consider a GFR of 60 or over to be normal, while a GFR of less than 60 may indicate kidney disease. A GFR level of 15 or less indicates kidney failure.

Kidney obstruction

A blockage in urine flow, such as an enlarged prostate or kidney stone, could cause kidney obstruction.

This blockage can create a backup of urine into the kidney and impair the kidney’s ability to function correctly. The medical term for this condition is hydronephrosis.

If obstructions affect both kidneys, this can raise a person’s blood creatinine levels.

Increased consumption of protein

What a person eats can have an effect on creatinine levels.

For example, proteins and cooked meat contain creatinine, so eating more than the recommended amount of meat or other proteins for a person’s activity levels can cause high creatinine levels after eating.

However, long-term studies have shown that high protein diets do not significantly impact blood creatinine levels over a 2-year period.

Intense exercise

Creatine is present in the muscles and helps them produce energy. Both dehydration and muscle breakdown from exercise may cause an increase in blood creatinine levels.

Certain medications

Antibiotics, such as trimethoprim, and H2 blockers, such as cimetidine, can cause a temporary increase in measured serum creatinine levels.

A 2020 retrospective study found that even low levels of trimethoprim can increase blood serum levels in patients following a kidney transplant.

Creatinine levels may be lower than normal for the following reasons:

Low muscle mass

Because the breakdown of muscle produces creatinine, low muscle mass can result in low levels of creatinine.

Older adults are more at risk, as muscle mass declines with age. Malnutrition can also cause low muscle mass and low creatinine levels.

Chronic conditions, such as myasthenia gravis or muscular dystrophy, may result in low creatinine levels.

Extreme weight loss

Weight loss can result in the reduction of muscle mass, leading to low levels of creatinine.

During pregnancy, blood flow to the kidneys is higher. This increases a person’s GFR and the rate of creatinine excretion.

Due to this, pregnant people typically have lower levels of blood creatinine.

A 2020 review found that the mean blood creatinine level in pregnant people is 77–84% of that in nonpregnant people. A person’s creatinine levels will also change across trimesters.

TrimesterMean creatinine levelUpper limit of creatinine level
First56 μmol/L (0.63 mg/dL)76 μmol/L (0.86 mg/dL)
Second52 μmol/L (0.59 mg/dL)72 μmol/L (0.81 mg/dL)
Third54 μmol/L (0.61 mg/dL)77 μmol/L (0.87 mg/dL)

Low creatinine levels mean something is affecting creatine production in the body. This will often result from a person having low muscle mass or body weight.

However, low creatinine levels may also indicate a person has chronic kidney disease, reduced kidney function, or malnutrition.

Learn more about low creatinine levels here.

High creatinine levels may also indicate severe kidney problems, such as infection or failure.

However, this will not always be the case. Antibiotics, diet, and dehydration from exercise can all impact creatine production. In these instances, creatinine levels may return to normal shortly after a person addresses the underlying cause.

Learn more about high creatinine levels here.

Dietary choices and physical activity play an essential role in regulating blood creatinine levels. It is advisable to keep protein consumption within the recommended range for age and activity level.

Creatinine levels outside of normal ranges may indicate an underlying condition. If a doctor can diagnose what may be causing abnormal creatinine levels, they can suggest suitable treatment options.

If levels persist at an abnormally high or low level, people may need to see a kidney specialist. Early treatment of rising or falling creatinine levels is essential to prevent more significant kidney disease.

The body produces creatinine at a steady rate, and measuring the levels only requires a routine blood sample.

Measuring creatinine levels is a useful way to identify the GFR, an indicator of overall kidney function. Doctors can use GFR levels to check for signs of chronic kidney disease.

A doctor or healthcare professional will carry out the blood test.

Before the test, they might ask questions related to:

  • diet
  • physical activity
  • supplements
  • current medications

It is best to discuss any medical conditions and any family history of kidney disease at the time of the blood test.

There is no need to avoid food or drink before the blood test.

The blood test involves collecting blood from a vein in the arm or hand. The doctor then sends the sample to a lab for analysis.

Adult males’ average creatinine level range is 60–110 μmol/L, while it is 45–90 μmol/L for females.

Creatinine is the waste product of creatine, which the body uses for energy. Doctors can use creatinine level tests to check for abnormalities in kidney function.

Dehydration, exercise, physical changes in pregnancy, and kidney failure can all impact creatinine levels.

A person will typically undergo creatinine level tests in a medical setting, meaning doctors will usually be able to quickly interpret results and plan the next steps.