At a Glance
Why Get Tested?
To screen for and monitor kidney dysfunction in those with known or suspected kidney disease
When to Get Tested?
When a health practitioner suspects that you may have decreased kidney function; it may be ordered at regular intervals when you have 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 all cells that contain a nucleus and is found in a variety of body fluids, including the blood. It is produced, filtered from the blood by the kidneys, and broken down at a constant rate. This test measures the amount of cystatin C in blood to help evaluate kidney function.
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 blood.
The rate at which the fluid is filtered is called the glomerular filtration rate (GFR). A decline in kidney function leads to decreases in the GFR and to increases in cystatin C and waste products such as creatinine in the blood.
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.
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, blood urea nitrogen (BUN), and eGFR (an estimate of the GFR usually calculated from the blood creatinine level). Unlike creatinine, cystatin C is not significantly affected by muscle mass (hence, gender or age), race, or diet, which has led to the idea that it could be a more reliable marker of kidney function and potentially used to generate a more precise estimate of 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. However, testing is becoming increasingly more available and steps are being taken toward standardizing the calibration of cystatin C results.
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.
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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
Lerma, E. (Updated 2012 May 17). Novel Biomarkers of Renal Function. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/1925619-overview through http://emedicine.medscape.com. Accessed July 2013.
Sinert, R. and Peacock, P. (Updated 2013 June 20). Acute Renal Failure Complications. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/777845-overview#a1 through http://emedicine.medscape.com. Accessed July 2013.
Malone, B. (2012 August 23). Refining the Role of Cystatin C in Estimating GFR New Combined Cystatin C –Creatinine Equation More Accurate. Clinical Laboratory Strategies [On-line information]. Available online at http://www.aacc.org/publications/strategies/archives/2012/Documents/082312CLS.pdf through http://www.aacc.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.
Paxton, A. (2012 September). Cystatin C and creatinine—using both found to be best. CAP Today [On-line information]. Available online through http://www.cap.org. 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 326-333.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 363-366.
McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 177.
Zhou H, Hewitt SM, Yuen PS, Star RA. Acute Kidney Injury Biomarkers - Needs, Present Status, and Future Promise. Nephrol Self Assess Program. Mar 2006;5(2):63-71. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2603572/ through http://www.ncbi.nlm.nih.gov. Accessed August 2013.
National Kidney and Urologic Diseases Information Clearninghouse. Kidney Disease Research Updates, Winter 2013. NIH-funded Study Finds More Precise Way to Estimate Kidney Function. Available online at http://kidney.niddk.nih.gov/About/ResearchUpdates/KidneyWin13/5.aspx through http://kidney.niddk.nih.gov. Accessed October 2013.
National Kidney Foundation. Cystatin C: What is its role in estimating GFR? Available online at http://www.kidney.org/professionals/tools/pdf/CystatinC.pdf through http://www.kidney.org. Accessed October 2013.
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 Disease Education Program. Update on Cystatin C: Cystatin C Standardization (Update as of July 2010). Available online at http://nkdep.nih.gov/lab-evaluation/cystatin-c.shtml through http://nkdep.nih.gov. Accessed October 2013.
UCSF (Karin Rush-Monroe on September 04, 2013). Kidney Function Can Be Assessed by Measuring Cystatin C in Blood. Available online at http://www.ucsf.edu/news/2013/09/108666/relationship-kidney-function-estimates-risk-improves-measuring-cystatin-c-blood through http://www.ucsf.edu. Accessed October 2013.
Shlipak MG et al. Cystatin C versus Creatinine in Determining Risk Based on Kidney Function. N Engl J Med 2013; 369:932-943, September 5, 2013. Available online at http://www.nejm.org/doi/full/10.1056/NEJMoa1214234 through http://www.nejm.org. Accessed October 2013.
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.
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.