Creatinine is a normal waste product that the body produces every day during muscle movements and when digesting meat. Healthy kidneys remove creatinine from the blood, and it leaves the body in urine.

High levels of creatinine in the urine can indicate diabetes, high muscle tone, or problems with the kidneys.

In this article, we take a closer look at the urine creatinine test, including its uses, the procedure, and what the results mean.

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A doctor may order a creatinine urine test to diagnose problems with the kidneys.

A creatinine urine test measures the levels of creatinine in the urine.

This test reveals a person's creatinine clearance rate, which is the amount of creatinine that the kidneys process per unit of time.

Creatinine levels vary throughout the day. Due to this, a doctor will often order a 24 hour urine sample test to get a more accurate measure of how much creatinine the kidneys are clearing.

For this type of urine test, the individual will need to collect all of the urine that they produce over 24 hours. Doctors will then send the urine sample to a laboratory for analysis.

If the amount of creatinine in the urine does not fall within the normal range, this could indicate that the kidneys are not functioning properly. This dysfunction may be due to kidney damage, kidney disease, or other health issues that can affect kidney function.

However, the amount of creatinine in a person's body varies widely depending on race, gender, age, and body size. This variation means that urine levels are a poor indicator of kidney problems. If a person has high creatinine levels in their urine, a doctor may need to order further tests to determine the cause.

Doctors may also order a blood test to check the amount of creatinine in a person's blood, which they will refer to as serum creatinine. To test for serum creatinine, doctors often use the glomerular filtration rate (GFR). A GFR test takes into account a person's age, race, gender, and body size when calculating creatinine levels.

The levels of creatinine in urine vary based on a person's age, sex, health history, and muscle mass. Higher levels may not necessarily indicate a health issue, but they can sometimes be due to kidney problems.

Doctors measure the typical ranges for creatinine levels in a 24 hour urine sample in either grams per day (g/day) or millimoles per day (mmol/day).

According to the University of Rochester Medical Center, normal ranges are as follows:

  • for males, 0.8–1.8 g/day or 7.0–16.0 mmol/day
  • for females, 0.6–1.6 g/day or 5.3–14.0 mmol/day

However, the reference ranges may vary among laboratories. The person's healthcare provider should be able to review the numbers and explain what the results mean and whether further tests are necessary.

When a person's urine creatinine levels do not fall within the normal range, this could be a sign of an issue with their kidneys. However, high levels do not always indicate a problem.

In some cases, having a lot of muscle can cause high creatinine levels in the body. Diets rich in protein can also lead to high creatinine levels.

Some medical issues that can cause high or low creatinine levels include:

The creatinine urine test typically takes place over 24 hours. A person may wish to schedule the test on a day when they can stay at home.

In preparing for the test, the person should talk to their doctor about:

  • any supplements or medications that they are taking
  • what time of day they should start collecting urine
  • if there are any drinks or foods that they should avoid ahead of or during the test
  • where they should return the container of urine to at the end of the 24 hours

The person should ask any questions about the process before starting to take samples. Not following the directions closely could skew the results of the test.

In addition, females should tell their doctor if they are or might be pregnant.

A doctor should provide specific instructions ahead of the test, but the following are some general guidelines of how to collect the urine:

  • Record the time and amount of the first urination of the test, but do not collect it. Doing this allows a person to start the 24 hours with an empty bladder.
  • Collect each urination throughout the next 24 hours and store the collected urine in the refrigerator.
  • Try to have the final urination of the test at the same time as the start of the collection period the previous day.
  • Seal the sample container and return it to the agreed place as soon as possible.

The person should tell their healthcare provider if there were any issues during the collection process. These may include:

  • being unable to collect all urine
  • collecting urine beyond the 24 hour mark
  • spilling urine
  • not storing the samples in a cold location

A creatinine urine test measures the amount of creatinine — a byproduct of muscle movement and meat digestion — in the urine. If creatinine levels fall outside the normal range, this does not always signal a problem, but it can sometimes indicate an issue with the kidneys.

A doctor will review the results of this noninvasive test. If the results are abnormal, a doctor is likely to order additional tests to check for kidney issues.