Tests for kidney disease

Many people with kidney disease don't know they have it until their kidneys are already damaged because they don't have any symptoms. This makes early testing important, especially if you're at increased risk due to factors like diabetes, high blood pressure, or a family history of kidney disease. Early detection and treatment can slow or even stop kidney disease from getting worse.

Learning about the tests, what they do and what to expect can help you and your doctor catch kidney disease early when it is most treatable. Doctors can help find the cause of kidney disease through these tests, make a personalized treatment plan, and help you improve your quality of life.

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Blood tests

Blood tests can look for and measure substances (such as antibodies or proteins) that are signs of other health problems that may cause kidney disease, such as lupus.  

eGFR test (Estimated Glomerular Filtration Rate) 

eGFR (estimated glomerular filtration rate) is a measure of how well your kidneys are working. Your eGFR is an estimated number that is calculated based on a blood test measuring creatinine — a waste product filtered by the kidneys — along with your age and sex. 

eGFR is considered a mostly reliable test for doctors to know how well your kidneys are working. However, the eGFR may not be accurate if you are younger than 18, pregnant, very overweight, or very muscular. 

In some cases, a cystatin C test may be used instead of creatinine to estimate GFR, as it can provide more accurate results.

Cystatin C Test

Your healthcare provider may use a blood test for cystatin C to calculate your eGFR. A cystatin C test may provide a more accurate estimate of kidney function, especially if there is concern about the reliability of creatinine-based results. Cystatin C is a protein made by cells in your body, and like creatinine, this protein is filtered by the kidneys. 

A cystatin C-based eGFR may be used if:  

• Past kidney function test results have come back unclear. 
• Your creatinine levels are likely to vary for other reasons, such as older age or having a lot of muscle mass, like a bodybuilder.

Serum creatinine test

Your serum creatinine level is based on a blood test that measures the amount of creatinine in your blood. It tells how well your kidneys are working. When your kidneys are not working well, your serum creatinine level goes up.

Your doctor can also measure creatinine with a urine test.

Blood urea nitrogen (BUN) test

Your blood urea nitrogen (BUN) level is based on a blood test that measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that your body makes after it breaks down protein. Healthy kidneys take urea nitrogen out of your blood. When your kidneys are not working well, your BUN level goes up. While this test is important, it's essential to remember that it's only one part of the bigger picture in assessing kidney health. Advocate for your health by working with your healthcare team to interpret all test results and build a comprehensive care plan.

Urine tests

A urine test is when a doctor examines a small amount of your urine (pee) to check for signs of kidney disease and other health problems. When your kidneys are damaged, they may let protein leak into your urine. This can be one of the earliest signs of kidney disease.

Urine tests help your doctor: 

• Measure your kidney function 
• Find out what stage of kidney disease you are in
• Keep track of health problems that can cause kidney disease, such as diabetes
• Check for complications (problems) from kidney disease, such as anemia and metabolic acidosis 
• Check for other problems such as a kidney infection or a urinary tract infection (UTI)

The UACR is a simple urine test: 

1. You will give a small sample of urine (about two tablespoons). 
2. Your urine sample is sent to a lab to see the amount of albumin (the main protein in your blood) and creatinine (a waste product in your blood that comes from your muscles). 
3. Your doctor will compare these levels to figure out your UACR. 

If your UACR is more than 30 mg/g, ask your doctor when you should get the test again.  

24-hour urine test 

This test is commonly used to measure excess protein in the urine, but it also measures other substances like sodium, potassium, and oxalates (compounds that can contribute to kidney stone formation), which can help detect specific kidney diseases or risk factors.

Your doctor will give you one or two large containers to collect your urine over a 24-hour period. They will also give you a special pan that fits in your toilet or a urinal to collect your urine. 

Nephrin test

Nephrin is a protein found in special cells in the kidneys called podocytes. Podocytes help your kidneys filter your blood.

A nephrin test looks for nephrin in your urine (pee). When nephrin is in your urine, it may mean the podocytes in your kidneys have been damaged and aren't helping filter your blood as they should. 

Imaging tests 

Imaging tests look for physical changes in your kidneys that may help find the cause of your kidney disease, such as:  

• Abnormal size or shape of your kidneys 
• Blood flow to your kidneys 
• Signs of injury or damage to your kidneys 
• Kidney stones, cysts (fluid-filled sacs) or tumors 
• Size of or problems with your bladder (the organ that stores urine before it leaves your body) 

After an imaging test, a radiologist (a doctor specially trained in reading scan images) will read your images and give the results to your doctor. You and your doctor will go over the results and decide your next steps.  

Remember, imaging tests should be interpreted in conjunction with other lab tests (e.g., eGFR, serum creatinine) to get a comprehensive view of kidney health. 

Kidney ultrasound 

A kidney ultrasound (also called a renal ultrasound) is a painless imaging test that uses sound waves to make pictures of your kidney. While the ultrasound itself isn't painful, having to lie still for the entire exam may cause some discomfort. Imaging can help evaluate kidney size, shape, and scarring, which are important for understanding CKD progression. You may be asked not to empty your bladder before the exam.

1. You will lie down on an exam table on your stomach. 
2. The ultrasound tech (the person doing the ultrasound) will spread a warm gel on over your kidney area.  
3. The tech will rub a transducer (a device that converts energy from one form to another) probe against your skin to send ultrasound waves. The waves reflect off of structures inside the body for evaluation. 

To examine your empty bladder, you will be asked to urinate after the ultrasound. A kidney ultrasound takes about 20-30 minutes.  

Computed tomography (CT or CAT) scan of the kidneys 

A CT or CAT scan is a painless test that uses X-rays and computer technology to create detailed images of your kidneys. It is often used when doctors need more detailed information than an ultrasound can provide. In some cases, doctors may recommend a contrast-enhanced CT scan, which uses a contrast dye to make the image clearer. If you have a scan with contrast, you will get the contrast (a substance you will drink or get through a needle in a vein that helps certain tissues show up more clearly). 

1. You will lie down on an exam table that slides into a large circle opening of a scan machine. 
2. The tech will move to another room to control the scan. You will be able to talk with the tech through a speaker system. 
3. The scanner will rotate around you, and you will hear clicking sounds. You will need to lie very still, and the tech may ask you to hold your breath. 
4. The tech will give you an IV to see if there is contrast in the vein, the tech will remove the IV after the scan.  

A CT scan takes about 30 to 60 minutes.  

Magnetic resonance imaging (MRI) of the kidneys 

An MRI uses magnets and radio waves to make 3D (3-dimensional) pictures of your kidneys. This test is often used when other image tests, like CT or ultrasound, are inconclusive. This allows for earlier detection of disease progression before kidney damage becomes visible through traditional imaging.

1. You will need to remove any metal objects, such as jewelry or watches. You should tell your doctor or the MRI technician if you have any metal objects inside your body, such as a pacemaker or metal plate.
2. You will lie down on an exam table that slides into a large tunnel-like tube in the scanner and stay very still
3. Some MRI scans involve an injection of contrast (dye) to allow tissues and blood vessels to be seen more clearly. It's possible for this dye to cause organ or tissue damage in people with severe kidney disease. Ask your doctor if you need to receive dye. If you have a history of kidney disease, you need a blood test to determine how well your kidneys function before proceeding with the MRI.
4. The tech will move to another room to control the scan. You will be able to talk with the tech through a speaker system. 
5. The scanner will take many sets of images. You will hear loud noises coming from the scanner. 

An MRI takes about 30 to 60 minutes. 

Kidney biopsy

A kidney biopsycan help your doctor figure out what is causing your kidney problem, how severe it is, and the best treatment. This involves removing a small piece of your kidney tissue for examination under a microscope.

Your doctor may suggest a kidney biopsy if tests show:

• Blood in your urine (hematuria) 
• Protein in your urine (proteinuria)
• Kidney disease with no clear cause
• Nephrotic syndrome (a group of symptoms that when happen together can show that your kidneys are not working as well as they should)
• Concern for glomerular or inflammatory kidney disease

Your doctor may also suggest a kidney biopsy to find out if:

• The treatment for your kidney problem is working
• There is damage to your kidneys that cannot be reversed
• A transplanted kidney is not working well
• You have a kidney tumor
• If your kidney problem is caused by a rare kidney disease 

If you have any questions about why you need a kidney biopsy and how it could help treat your kidney problem, talk to your doctor. 

After the biopsy, you will be closely monitored for 24-48 hours to ensure there are no complications, including bleeding. Your doctor will review the biopsy results and use them to make decisions about your treatment plan.

Learn more about a kidney biopsy.

Genetic Testing

Genetic testing looks at your DNA, the genetic code that is unique to every individual.  

This testing uses a blood or saliva (spit) sample to look at changes in your genes, chromosomes or proteins. Genes are the information inside your cells that instruct it to do certain tasks, chromosomes are structures within your body's cells that contain your genes, and proteins are built from the cells using instructions found in your genes. Changes, or mutations, in your genes may cause certain types of kidney disease.  

Results from a genetic test can help doctors confirm or rule out a genetic condition or help you better understand your chances of developing or passing on a genetic disorder.  

Genetic testing may help your healthcare team to diagnose, monitor and manage certain types of kidney diseases. This type of testing can be helpful if you have a family history of kidney disease or if you don't know the cause of your kidney disease.  

You may want to consider working with a genetic counselor before or after genetic testing. They can tell you what test results mean and help support you and your family to make decisions based on your genetic testing results, and offer helpful information to your healthcare team.   

Genetic testing is not only used for diagnosis but also for personalized medicine. Your doctor may be able to tailor your treatments based on genetic information. 

How much does it cost for a kidney test?

The costs of these tests depend on your insurance coverage. Call your insurance company and ask if they cover a test and how much you may have to pay. If your insurance will not cover a test, there may be programs to help you pay.  

Ask your doctor to speak with a social worker or financial counselor for help with insurance and paying for tests.  

As a patient, it's crucial to stay informed, ask questions, and actively participate in your treatment. Your role as your own advocate is how you ensure you receive the best care possible. Partner with your healthcare team, ask about all test results and make sure you have a complete care plan for your long-term health.