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At a Glance
Why Get Tested?
To assess kidney function and diagnose, stage, and monitor chronic kidney disease (CKD)
When to Get Tested?
When your health practitioner thinks that you may have kidney damage or that you may be at risk for developing kidney disease
A blood sample drawn from a vein in your arm; the eGFR is a calculated estimate of the actual glomerular filtration rate and is based on your blood creatinine level along with other variables that may include your age, sex, and race as well as possibly your height and weight, depending on the equation used.
Test Preparation Needed?
The Test Sample
What is being tested?
Glomerular filtration rate (GFR) is a measure of the function of the kidneys. This test measures the level of creatinine in the blood and uses the result in a formula to calculate a number that reflects how well the kidneys are functioning, called the estimated GFR or eGFR.
Glomeruli are tiny filters in the kidneys that allow waste products to be removed from the blood, while preventing the loss of important constituents, including proteins and blood cells. Every day, healthy kidneys filter about 200 quarts of blood and produce about 2 quarts of urine. The GFR refers to the amount of blood that is filtered by the glomeruli per minute. As a person's kidney function declines due to damage or disease, the filtration rate decreases and waste products begin to accumulate in the blood.
Chronic kidney disease (CKD) is associated with a decrease in kidney function that is often progressive. CKD can be seen with a variety of conditions, including diabetes and high blood pressure. Early detection of kidney dysfunction can help to minimize the damage. This is important as symptoms of kidney disease may not be noticeable until as much as 30-40% of kidney function is lost.
A measured GFR is considered the most accurate way to detect changes in kidney status, but measuring the GFR directly is complicated, requires experienced personnel, and is typically performed only in research settings. Because of this, the eGFR is usually used.
The eGFR is a calculation based on a serum creatinine test. Creatinine is a muscle waste product that is filtered from the blood by the kidneys and excreted into the urine at a relatively steady rate. When kidney function decreases, less creatinine is excreted and concentrations increase in the blood. With the creatinine test, a reasonable estimate of the actual GFR can be determined.
The most commonly used equation for calculating the eGFR, and the one currently recommended by the National Kidney Foundation (NKF) for general use, is called the MDRD (Modification of Diet in Renal Disease Study) equation. It requires a person's serum creatinine, age, and assigned values based upon sex and race.
According to the NKF, as of January 2013, many large commercial clinical laboratories have changed from using the MDRD equation for eGFR reporting to a slightly different one that uses the same factors, the CKD-EPI equation, published in 2009. The results reported using one equation versus the other will not be identical but should give the health practitioner similar information.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm. Depending on the formula used, a person's age, sex, race, height, and weight may also be needed.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Turin, T. et. al. (2013) Change in the Estimated Glomerular Filtration Rate Over Time and Risk of All-Cause Mortality. Medscape Today News from Kidney Int. v83 (4):684-691 [On-line information]. Available online at http://www.medscape.com/viewarticle/782622 through http://www.medscape.com. Accessed July 2013.
Simon, J. et. al. (2011 March). Interpreting the estimated glomerular filtration rate in primary care: Benefits and pitfalls. Cleveland Clinic Journal of Medicine v78 (3) 189-195. [On-line information]. Available online at http://www.ccjm.org/content/78/3/189.full through http://www.ccjm.org. Accessed July 2013.
(© 1995–2013). Cystatin C with Estimated GFR, Serum. Mayo Clinic Mayo Medical Laboratory Interpretive Handbook [On-line information]. Available online at http://www.mayomedicallaboratories.com/interpretive-guide/?alpha=C&unit_code=35038 through http://www.mayomedicallaboratories.com. Accessed July 2013.
(Updated 2012 July 10) For People with Diabetes or High Blood Pressure: Get Checked for Kidney Disease. National Kidney Disease Education Program [On-line information]. Available online at http://www.nkdep.nih.gov/resources/get-checked-kidney-disease.shtml through http://www.nkdep.nih.gov. Accessed July 2013.
Dugdale, D. (Updated 2011 September 19). Glomerular filtration rate. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/007305.htm through http://www.nlm.nih.gov. Accessed July 2013.
Shah, A. (Revised 2013 May). Evaluation of the Renal Patient. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed July 2013.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 329-333.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 362-364.
McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 173-177.
National Kidney Disease Education Program. Estimating GFR. Available online at http://nkdep.nih.gov/lab-evaluation/gfr/estimating.shtml through http://nkdep.nih.gov. Accessed October 2013.
National Kidney Foundation. Cystatin C: What is its role in esimating GFR? Available online at http://www.kidney.org/professionals/tools/pdf/CystatinC.pdf through http://www.kidney.org. Accessed October 2013.
Sources Used in Previous Reviews
National Kidney Foundation. DOQI: Clinical Practice Guidelines. Available online at http://www.kidney.org/professionals/kdoqi/guidelines through http://www.kidney.org.
National Kidney Foundation. Glomerular Filtration Rate. Available online at http://www.kidney.org/kidneydisease/ckd/knowGFR.cfm through http://www.kidney.org.
National Kidney Foundation. Kidney Learning System: GFR. Available online at http://www.kidney.org/professionals/KLS/gfr.cfm through http://www.kidney.org.
Levey et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Annals of Internal Medicine. 1999; 130(6):461-470.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 311-312.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 438-439.
Patel, P. (Updated 2009 August 12). Glomerular filtration rate. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/007305.htm. Accessed October 2009.
(2009 February). The Kidneys and How They Work. National Kidney and Urologic Diseases Information Clearinghouse [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/ through http://kidney.niddk.nih.gov. Accessed October 2009.
(Reviewed 2009 April 7). Laboratory Professionals, Estimating and Reporting GFR. National Kidney Disease Education Program [On-line information]. Available online at http://www.nkdep.nih.gov/labprofessionals/estimate_report_gfr.htm through http://www.nkdep.nih.gov. Accessed October 2009.
Delgado, J. (Updated 2009 August). Renal Function Markers - Kidney Disease. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/RenalFunctionMarkers.html?client_ID=LTD# through http://www.arupconsult.com. Accessed October 2009.
(© 2007). Estimated Glomerular Filtration Rate (eGFR), in the Detection and Assessment of Chronic Kidney Disease in Adults. LabCorp Technical Review [On-line information]. PDF available for download at https://www.labcorp.com/pdf/Estimated_Glomerular_Filtration_Rate_eGFRL1137_1207_2.pdf through https://www.labcorp.com. Accessed October 2009.
(Reviewed 2007 October). Glomerular Filtration Rate, Estimated (eGFR). Quest Diagnostics Test Summary [On-line information]. Available online at http://www.questdiagnostics.com/hcp/intguide/jsp/showintguidepage.jsp?fn=TS_eGFR.htm through http://www.questdiagnostics.com. Accessed October 2009.