Learning About Monitoring Kidney Function

What is kidney function?

How well your kidneys work is called kidney function. Your kidneys have the important job of filtering your blood. They remove waste products and extra fluid from your body.

Why is it important to check kidney function?

When your kidneys do not work as they should, waste can build up in your blood. This can make you sick. If you have long-term (chronic) kidney disease, you may not have any symptoms until your kidney function is very low.

Blood and urine tests can help show how well your kidneys are working. They can help your doctor know:

• If the disease started all of a sudden or if you have had it a long time.
• The cause of the kidney damage.
• The best type of treatment to slow the damage.
• How well treatment is working.
• When to begin dialysis or have a kidney transplant.

What tests might be used?

• A creatinine clearance test measures how well your kidneys are filtering your blood. If your creatinine clearance goes down, this means your kidneys are not filtering your blood as well.
• A blood creatinine test shows the level of a waste product called creatinine in your blood. A high blood creatinine level may mean your kidneys are not working as they should.
• Urine tests measure certain substances, such as protein, in your urine. These tests may be done over 24 hours. Or you may do a one-time sample. Kidney damage can cause increased protein in the urine. This is because the kidneys cannot filter protein as well as they used to.
• A blood urea nitrogen (BUN) test measures the amount of nitrogen in your blood. This comes from a waste product called urea. If your kidneys can't remove urea from the blood normally, your BUN level rises.

How often should you be tested?

Experts recommend screening tests for people who are at higher risk of the disease. This includes people with diabetes or high blood pressure. If you have diabetes, your doctor may recommend yearly testing for protein in your urine. When to begin testing depends on the type of diabetes you have.