Kidney Function Tests

What are kidney function tests?

Kidney function tests are urine or blood tests that evaluate how well your kidneys are working. Most of these tests measure glomerular filtration rate (GFR). GFR assesses how efficiently your kidneys clear waste from your system.

What do your kidneys do?

Your kidneys are part of your urinary system. The two kidneys sit in the back of your abdomen just below your ribcage. They help your body filter waste materials and expel them as urine. Your kidneys are also vital for producing:

• Hormones that maintain blood pressure.
• Red blood cells, which carry oxygen throughout your body.
• Vitamin D, which maintains bone and muscle health.

Why might I need a kidney function test?

Some conditions, such as diabetes or high blood pressure (hypertension), affect how well the kidneys work. If you have one of these conditions, your healthcare provider may use kidney function tests to help monitor these conditions.

You may also need a kidney function test if you have symptoms that indicate possible kidney problems. These symptoms might include:

• Blood in your urine (hematuria).
• Painful urination (dysuria).
• Frequent urge to urinate.
• Problems with starting to pee.

What are the types of kidney function tests?

Your healthcare provider may order one or a few different types of kidney function tests. You may have blood tests for kidney function, such as:

• Blood urea nitrogen (BUN) measures nitrogen (made from protein breakdown) in your blood.
• Estimated GFR (eGFR) calculates filtration rates based on your protein levels, age, gender, size and race.
• Serum creatinine looks for the buildup of creatinine, a waste product from muscle tissue breakdown.

Your healthcare provider may also use 24-hour urine tests, including:

• Microalbuminuria looks for a specific protein called albumin.
• Urinalysis evaluates your urine for blood, proteins and function.

What happens during a kidney urine test?

You complete 24-hour urine tests at home. For a 24-hour urine test, your provider will give you a container to collect urine. On the day of the test:

1. Urinate into the toilet as usual after you first wake up.
2. For the rest of the day, urinate into the container.
3. On day two, urinate into the container when you first wake up.
4. Complete the test by dropping your sample off at the healthcare provider’s office or laboratory.

What happens during a kidney blood test?

For a kidney blood test, you visit your provider’s office or laboratory to give a blood sample. A technician uses a small needle and test tube to collect a blood sample.

What can I expect after a kidney test?

Kidney function tests are typically simple and cause no side effects. After blood tests, some people experience:

• Bruising.
• Dizziness.
• Fatigue.

Blood tests and urine tests typically don’t cause long-term pain or complications. Call your healthcare provider if you have pain, fatigue, or other symptoms that don’t go away.

When should I know the results of a kidney function test?

How soon you receive test results can vary. Sometimes, your provider discusses the results of your test on the same day. Or your provider may send the test to a lab, and you receive results in a few days.

What do the results of my kidney function test mean?

Kidney function test results can tell you whether your kidneys are functioning typically or not. Most function tests look for two measurements:

• GFR of less than 60 could indicate kidney disease.
• Urine albumin-to-creatinine ratio (UACR) of more than 30 milligrams per gram could be a warning sign of kidney disease.

What if my test results show early kidney disease?

If a test shows irregular results, your healthcare provider will follow up with you about treatment options. You may receive medications to manage blood pressure. Or you may follow up with a nephrologist (a doctor who specializes in the kidneys).

If your test results are atypical, your provider will likely order more frequent kidney function tests in the future. Regular testing helps your provider track your health and any underlying conditions.

A note from Cleveland Clinic

Kidney function tests check how well your kidneys are working. Healthy kidneys assist with removing waste from your body. Conditions such as diabetes or high blood pressure can affect your kidney function. You may also need a kidney function test to diagnose or rule out an infection. Kidney function tests include blood tests or urine tests. Typically, your provider gives you your results the same day or within a few days.