This test measures the level of a substance called creatinine in your urine.
Creatinine is a waste product that your body makes when you use your muscles. It's also made when your body digests meat. Healthy kidneys remove creatinine from your blood, and it leaves your body in your urine.
This test can find out whether your kidneys are working normally or to see if treatment for kidney disease is working.
You may need this test if your doctor suspects you have a problem with your kidneys. Signs and symptoms of kidney disease include:
Swelling in your feet or ankles
Puffiness around your eyes
Dry, itchy skin
Blood in your urine
You may also have this test if you have already been diagnosed with chronic kidney disease, so that your doctor can check your kidney function regularly and adjust your treatment if needed.
Your doctor may also order a protein-to-creatinine ratio test done on your urine. This will look at the amount of protein compared with creatinine. Excess protein that has leaked into your urine may be a sign of kidney disease.
Your doctor may also order blood tests to measure your kidney function. These might include a creatinine blood test and a blood urea nitrogen, or BUN, test. The creatinine blood test is used to find out your creatinine clearance, which gives a good measure of kidney function.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Results are given in grams per day (g/day) or millimoles per day (mmol/day). Normal results depend on your muscle mass, so the ranges differ for men and women:
Male: 0.8 to 1.8 g/day (7 to 16 mmol/day)
Female: 0.6 to 1.6 g/day (5.3 to 14 mmol/day)
Higher levels may mean that you have kidney disease.
This test requires a urine sample. Your doctor may need a "spot" urine test or a 24-hour test.
For "spot" urine test, you collect one sample, preferably early in the morning.
For a 24-hour urine sample, you must collect all the urine you produce for 24 hours. Empty your bladder completely first thing in the morning without collecting it and note the time. Then collect your urine every time you go to the bathroom for the next 24 hours.
This test poses no known risks.
If you are muscular, your urine creatinine level may be higher than normal. If you have little muscle mass because of disease, your urine creatinine level will likely be lower than normal.
If you are a non-Hispanic black or Mexican American, your urine creatinine level will be higher than the normal for non-Hispanic whites.
Certain medications may also affect your results.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.