GFR, EGFR

This test is used for screening to look for evidence of kidney damage (EGFR) or for changes in kidney function if you already have kidney disease (GFR).

EGFR is calculated from your age, weight, gender, and serum creatinine (requires a blood sample from a vein in your arm); in some formulas, race is also used in the calculation. GFR is calculated from serum and urine creatinine. It requires a blood sample from a vein in your arm and a 24-hour collection of urine.

Glomerular filtration rate (GFR) is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood, while preventing loss of important proteins and blood cells. The rate refers to the amount of blood that is filtered per minute. Estimated glomerular filtration rate (EGFR) is an estimate of the actual GFR. GFR is considered the most accurate way to detect changes in kidney status. While measurement of serum BUN (urea nitrogen) and creatinine are easier to do, they cannot pick up early damage to the kidneys. If kidney damage is detected early, it may be possible to prevent worsening damage to the kidneys with treatment of high blood pressure, diabetes, or other diseases that can damage the kidney.

SAMPLE COLLECTION

A blood sample is taken by needle from a vein in the arm; your weight and age are needed for EGFR as well. GFR requires both a blood sample taken from a vein in your arm and a 24-hour sample of urine.

NORMAL FINDINGS

Your lab will provide a range of normal values with your test results.

MEANING OF TEST

Your caregiver will go over your test results with you and discuss the importance of this test. Reference values are dependent on many factors, including patient age, gender, sample population, and testing method. Numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test.

EGFR can detect most types of kidney disease in their earliest changes. A normal EGFR means that kidney disease is unlikely. A low EGFR suggests that some kidney damage has occurred. GFR results are usually evaluated in the same way. Sometimes, in very early kidney damage (especially when the kidneys are damaged by diabetes), EGFR and GFR may actually be high, indicating that the kidneys are working harder than normal.

The American Kidney Foundation has suggested that all persons "know their GFR number." They recommend interpreting GFR (usually by EGFR) based on the following information:

KIDNEY DAMAGE STAGE: 1

  • DESCRIPTION: Kidney damage with normal or high GFR

  • GFR: 90+

KIDNEY DAMAGE STAGE: 2

  • DESCRIPTION: Mild decrease in GFR

  • GFR: 60-89

KIDNEY DAMAGE STAGE: 3

  • DESCRIPTION: Moderate decrease in GFR

  • GFR: 30-59

KIDNEY DAMAGE STAGE:4

  • DESCRIPTION: Severe decrease in GFR

  • GFR: 15-29

KIDNEY DAMAGE STAGE: 5

  • DESCRIPTION: Kidney failure

  • GFR: Less Than 15

Additionally in Stage 1, Protein or albumin in urine are high, cells or casts are seen in urine.

GFR and EGFR increase during pregnancy.

OBTAINING THE TEST RESULTS

  • Make sure you receive the results of your test. Ask as to how these results are to be obtained if you have not been informed. It is your responsibility to obtain your test results.

  • Your caregiver will provide further instructions or treatment options if necessary.