Kidney function tests are simple procedures that use either the blood or urine to help identify issues in the kidneys. There are a few different types of kidney function tests that investigate various aspects of kidney function.
A kidney function test may check to see if the kidneys are filtering waste products too slowly. Another type of test may see if the kidneys are leaking proteins into the urine.
A doctor who thinks a person may have a problem with their kidneys may order a kidney function test, but regular testing can be helpful for all adults.
Symptoms of kidney problems
Symptoms that may indicate a problem with your kidneys include:
- high blood pressure
- blood in the urine
- frequent urges to urinate
- difficulty beginning urination
- painful urination
- swelling of the hands and feet due to a buildup of fluids in the body
A single symptom may not mean something serious. However, when occurring simultaneously, these symptoms suggest that your kidneys aren’t working properly. Kidney function tests can help determine the reason.
Kidney function tests
Kidney function tests are common lab tests used to evaluate how well the kidneys are working. Such tests include:
- BUN (Blood urea nitrogen)
- Creatinine – blood
- Creatinine clearance
- Creatinine – urine
A urinalysis screens for the presence of protein and blood in the urine. There are many possible reasons for protein in your urine, not all of which are related to disease. Infection increases urine protein, but so does a heavy physical workout. Your doctor may want to repeat this test after a few weeks to see if the results are similar.
Your doctor may also ask you to provide a 24-hour urine collection sample. This can help doctors see how fast a waste product called creatinine is clearing from your body. Creatinine is a breakdown product of muscle tissue.
Serum creatinine test
This blood test examines whether creatinine is building up in your blood. The kidneys usually completely filter creatinine from the blood. A high level of creatinine suggests a kidney problem.
According to the National Kidney Foundation (NKF), a creatinine level higher than 1.2 milligrams/deciliter (mg/dL) for women and 1.4 mg/dL for men is a sign of a kidney problem.
Blood urea nitrogen (BUN)
The blood urea nitrogen (BUN) test also checks for waste products in your blood. BUN tests measure the amount of nitrogen in the blood. Urea nitrogen is a breakdown product of protein.
However, not all elevated BUN tests are due to kidney damage. Common medications, including large doses of aspirin and some types of antibiotics, can also increase your BUN. It’s important to tell your doctor about any medications or supplements that you take regularly. You may need to stop certain drugs for a few days before the test.
A normal BUN level is between 7 and 20 mg/dL. A higher value could suggest several different health problems.
This test estimates how well your kidneys are filtering waste. The test determines the rate by looking at factors, such as:
- test results, specifically creatinine levels
Any result lower than 60 milliliters/minute/1.73m2 may be a warning sign of kidney disease.
Kidney function tests are a vital part of diagnosing and treating disorders that affect the kidneys. Even if a person does not yet have symptoms, some people may need to undergo regular testing.
The National Institute of Diabetes and Digestive and Kidney Diseases recommend that people at higher risk for kidney issues receive regular kidney function tests. People at high risk include those with:
- high blood pressure
- heart disease
- a family history of kidney disease or kidney failure
Regular kidney function tests can help identify problems in the kidneys early and when the outlook is best.
By following a treatment plan, people can help prevent progression of the condition. Working directly with a doctor is the best way to monitor and manage any signs of kidney damage or underlying conditions.