At a Glance
Why Get Tested?
When to Get Tested?
When a doctor suspects that a person may have decreased kidney function, especially when a patient has normal creatinine and eGFR test results; may be ordered at intervals when a person has known kidney dysfunction
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Cystatin C is a relatively small protein that is produced throughout the body by nucleated (containing a nucleus) cells. It is produced and destroyed at a constant rate and is found in a variety of body fluids, such as blood, spinal fluid, and breast milk.
Cystatin C is filtered out of the blood by the glomeruli, clusters of tiny blood vessels in the kidneys that allow water, dissolved substances, and wastes to pass through their walls while retaining blood cells and larger proteins. What passes through the walls of the glomeruli forms a filtrate fluid. From this fluid, the kidneys reabsorb Cystatin C, glucose, and other substances. The remaining fluid and wastes are carried to the bladder and excreted as urine. The reabsorbed Cystatin C is then broken down and is not returned to the bloodstream.
The rate at which the fluid is filtered is called the glomerular filtration rate (GFR). Decreases in kidney function lead to decreases in the GFR and to increases in Cystatin C and waste products in the blood.
Because Cystatin C levels fluctuate with changes in GFR, there has been interest in the Cystatin C test as one method of evaluating kidney function. Tests currently used include creatinine, a byproduct of muscle metabolism that is measured in the blood and urine, BUN (Blood Urea Nitrogen), and eGFR – an estimate of the GFR. Unlike creatinine, Cystatin C is not significantly affected by muscle mass, gender, age, or race. When the kidneys are functioning normally, concentrations of Cystatin C in the blood are stable, but as kidney function deteriorates, the concentrations begin to rise. This increase occurs as the GFR falls and is often detectable before there is a measurable decrease in the GFR. While there are growing data and literature supporting the use of Cystatin C, there is still a degree of uncertainty about when and how it should be used.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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.
Ask a Laboratory Scientist
Form temporarily unavailable
Due to a dramatic increase in the number of questions submitted to the volunteer laboratory scientists who respond to our users, we have had to limit the number of questions that can be submitted each day. Unfortunately, we have reached that limit today and are unable to accept your inquiry now. We understand that your questions are vital to your health and peace of mind, and recommend instead that you speak with your doctor or another healthcare professional. We apologize for this inconvenience.
This was not an easy step for us to take, as the volunteers on the response team are dedicated to the work they do and are often inspired by the help they can provide. We are actively seeking to expand our capability so that we can again accept and answer all user questions. We will accept and respond to the same limited number of questions tomorrow, but expect to resume the service, 24/7, as soon as possible.
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
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 328-329.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 312.
Lowry, F. (2009 February 27). Cystatin C, High Levels of Serum Cystatin C and Chronic Kidney Disease Linked to Age-Related Macular Degeneration. Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/588857 through http://www.medscape.com. Accessed October 2009.
Ma, Y-C. et. al. (2008 January 28). Improved GFR Estimation by Combined Creatinine and Cystatin C Measurements. Medscape Today from Kidney International [On-line information]. Available online at http://www.medscape.com/viewarticle/568609 through http://www.medscape.com. Accessed October 2009.
Craig, R. G. and Hunder, J. M. (2008 October 27). Recent Developments in the Perioperative Management of Adult Patients with Chronic Kidney Disease. Medscape Today from British Journal of Anaesthesia [On-line information]. Available online at http://www.medscape.com/viewarticle/581312 through http://www.medscape.com. Accessed October 2009.
(2009 January 27). New Equation Accurately Estimates GFR in Children With Kidney Disease. Medscape Today from Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/587379 through http://www.medscape.com. Accessed October 2009.
(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.
(April 7, 2009) National Kidney Disease Education Program, Laboratory Professionals: Update on Cystatin C. Available online at http://nkdep.nih.gov/labprofessionals/update-cystatin-c.htm through http://nkdep.nih.gov. Accessed January 2010.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pp 153-154.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Jeffrey, S. (2006 August 16). Cystatin C May Identify Pre-CKD in Elderly With Normal eGFR. Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/543019 through http://www.medscape.com.
Jeffrey, S. (2005 September 6). Cystatin C is a sensitive marker of prognosis acute heart failure. Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/538789 through http://www.medscape.com.
Shlipak, M. (2005 May 19). Cystatin C and the Risk of Death and Cardiovascular Events among Elderly Persons. NEJM v 352(20) 2049-2060 [On-line journal]. Available online at http://content.nejm.org/cgi/content/short/352/20/2049 through http://content.nejm.org.
Sarnak, M. (2005 April 5). Cystatin C Concentration as a Risk Factor for Heart Failure in Older Adults. Annals of Internal Medicine v142(7) [On-line information]. Available online at http://www.annals.org/cgi/content/abstract/142/7/497?ct through http://www.annals.org.
Villa, P. et. al. (2005 April). Serum cystatin C concentration as a marker of acute renal dysfunction in critically ill patients. Crit Care. 2005; 9(2): R139-R143 [On-line journal]. Available online at http://www.pubmedcentral.gov/articlerender.fcgi?tool=pmcentrez&artid=1175926 through http://www.pubmedcentral.gov.