Glomerular filtration rate Health Article

Definition

Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the tiny filters in the kidneys, called glomeruli, each minute.

See also:

• Creatinine - clearance
• Creatinine - serum
• Creatinine - urine

Alternative Names

GFR; Estimated GFR; eGFR

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The blood sample is sent to a lab, where the creatinine level is tested. The lab specialist uses combines your creatinine level with several other factors to estimate your glomerular filtration rate (GFR). Different formulas are used for adults and children. The formula will include some or all of the following:

• Age
• Creatinine measurement
• Gender
• Height
• Race
• Weight

How to prepare for the test

Certain drugs can interfere with test results. Tell your doctor about all medicines you are taking, including over-the-counter ones.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there might be some throbbing.