Kidney Function Tests
What is a kidney function test?
You have two kidneys. They are fist-sized organs on either side of your backbone above your waist. Your kidneys filter and clean your blood, taking out waste products and making urine.
Kidney tests check to see how well your kidneys are working. They include blood, urine, and imaging tests.
What is it used for?
Early kidney disease usually does not have signs or symptoms. Testing is the only way to know how your kidneys are doing.
Why do I need a kidney function test?
You need to get checked for kidney disease if you have the key risk factors:
- High blood pressure
- Heart disease
- A family history of kidney failure
If you have diabetes, get checked every year. If you have high blood pressure, heart disease, or a family history of kidney failure, talk with your health care provider or Care Team about how often you should get tested. The sooner you know you have kidney disease, the sooner you can get treatment to help protect your kidneys.
What test could be performed?
Specific kidney tests include:
- Glomerular filtration rate (GFR) – one of the most common blood tests to check for chronic kidney disease. It tells how well your kidneys are filtering.
- Creatinine blood and urine tests - check the levels of creatinine, a waste product that your kidneys remove from your blood
- Albumin urine test – checks for albumin, a protein that can pass into the urine if the kidneys are damaged
- Imaging tests, such as an ultrasound - provide pictures of the kidneys. The pictures help the health care provider see the size and shape of the kidneys and check for anything unusual.
- Kidney biopsy – a procedure that involves taking a small piece of kidney tissue for examination with a microscope. It checks for the cause of kidney disease and how damaged your kidneys are.
Glomerular filtration rate
Your health care provider will use a blood test to check your kidney function. The results of the test mean the following:
- AGFR of 60 or more is in the normal range. Ask your health care provider or Care Team when your GFR should be checked again.
- AGFR of less than 60 may mean you have kidney disease. Talk with your health care provider or Care Team about how to keep your kidney health at this level.
- AGFR of 15 or less is called kidney failure. Most people below this level need dialysis or a kidney transplant. Talk with your health care provider or Care Team about your treatment options.
You can’t raise your GFR, but you can try to keep it from going lower.
Creatinine is a waste product from the normal breakdown of muscles in your body. Your kidneys remove creatinine from your blood. Providers use the amount of creatinine in your blood to estimate your GFR. As kidney disease gets worse, the level of creatinine goes up.
If you are at risk for kidney disease, your provider may check your urine for albumin.
Albumin is a protein found in your blood. A healthy kidney doesn’t let albumin pass into the urine. A damaged kidney lets some albumin pass into the urine. The less albumin in your urine, the better. Having albumin in the urine is called albuminuria.
A health care provider can check for albumin in your urine in two ways:
Dipstick test for albumin
A provider uses a urine sample to look for albumin in your urine. You collect the urine sample in a container in a health care provider’s office or lab. For the test, a provider places a strip of chemically treated paper, called a dipstick, into the urine. The dipstick changes color if albumin is present in the urine.
Urine albumin-to-creatinine ratio (UACR)
This test measures and compares the amount of albumin with the amount of creatinine in your urine sample. Providers use your UACR to estimate how much albumin would pass into your urine over 24 hours. A urine albumin result of:
- 30 mg/g or less is normal
- More than 30 mg/g may be a sign of kidney disease
If you have albumin in your urine, your provider may want you to repeat the urine test one or two more times to confirm the results. Talk with your provider about what your specific numbers mean for you.
If you have kidney disease, measuring the albumin in your urine helps your provider know which treatment is best for you. A urine albumin level that stays the same or goes down may mean that treatments are working.
Ultrasound uses a hand-held device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. The health care professional can move the transducer at different angles to examine different organs.
This procedure is painless, poses no risk of radiation, needs no anesthesia, and allows you to return to daily tasks immediately. Health care professionals use specific types of abdominal ultrasounds to look at different parts of the urinary tract.
A kidney ultrasound can show if the kidneys are in the right place or if they have blockages, kidney stones, or tumors.
A kidney biopsy is a procedure that involves taking a small piece of kidney tissue for examination with a microscope. A pathologist — a doctor who specializes in diagnosing diseases — examines the kidney tissue sample in a lab. The pathologist looks for signs of kidney disease or infection.
The kidney tissue sample can show inflammation, scarring, infection, or unusual deposits of a protein called immunoglobulin. If a person has chronic kidney disease — any condition that causes reduced kidney function over a period of time — the biopsy may show how quickly the disease is advancing.
How do I know if my kidney health is getting worse?
You can keep track of your test results over time. You can tell that your treatments are working if your:
- GFR stays the same
- Urine albumin stays the same or goes down
Your health care provider or Care Team will work with you to manage your kidney disease.
Source: MedlinePlus, National Library of Medicine, National Institute of Diabetes and Digestive and Kidney Diseases