eGFR Creatinine-Cystatin C Calculation

CPT: To be determined. Updates will be made when available.

Test Includes

Creatinine, serum; cystatin C; eGFR Creatinine-Cystatin C Calculation


Expected Turnaround Time

2 - 5 days


Related Documents

For more information, please view the literature below.

eGFR Calculation with Cystatin C and Creatinine - white paper


Specimen Requirements


Specimen

Serum or plasma


Volume

1.5 mL


Minimum Volume

1 mL


Container

Red-top tube, gel-barrier tube, or green-top (heparin) tube


Collection

Separate serum or plasma from red blood cells.


Storage Instructions

Room temperature


Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3


Causes for Rejection

Specimen other than serum or heparinized plasma; grossly hemolyzed (>1,000 mg/dL Hgb) samples; excessive turbidity and clots in samples


Test Details


Use

An estimated 37 million U.S. adults have chronic kidney disease (CKD). In addition to cardiovascular-associated events, they are at risk for kidney failure or end-stage kidney disease (ESKD) requiring dialysis or kidney transplant. In the 2015-2016 National Health and Nutrition Examination Survey, prevalence of CKD stages G1-4 was 14.2% among adult participants. One in three U.S. adults is at risk for CKD due to prevalent risk factors such as diabetes and/or high blood pressure. The incidence of CKD is projected to increase during the next 20 years because of increasing obesity rates and an aging U.S. population.1

Early-stage CKD is often asymptomatic, making laboratory testing imperative for at-risk patients. This typically includes two tests, a serum creatinine with estimated glomerular filtration rate(eGFR), a test of kidney function, and a urine albumin-to-creatinine ratio (uACR), a test of kidney damage. While eGFR results are commonly reported as part of metabolic panels, this test alone is insufficient for CKD detection: The presence of albuminuria reflects endothelial inflammation that may cause proximal tubular damage and progressive kidney function loss.1

Asymptomatic individuals with diabetes, hypertension, family history of kidney disease and cardiovascular disease are considered to be at high risk for CKD and should be tested at least annually for eGFR and albuminuria.2 Additionally, total urine protein measurements may be warranted in some individuals to detect other etiologies of CKD missed by urine albumin measurements.3

The Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guidelines suggest measurement of cystatin C, an alternative endogenous filtration marker, in specific circumstances when GFR estimates based on serum creatinine are thought to be less accurate and when decisions depend on more accurate knowledge of GFR, such as confirmation of CKD diagnosis, determining eligibility for transplant or adjusting dosage of drugs excreted by the kidney.4

A 2021 report from the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases recommended increased, routine and timely use of cystatin C combined with creatinine as a confirmatory assessment of kidney function, because combining filtration markers (creatinine and cystatin C) for eGFR calculation is more accurate and would support better clinical decisions than either marker alone. A new eGFR equation, the CKD-EPI 2021 eGFR creatinine-cystatin C equation without a race variable, was recommended for clinical use.5,6 More recently, the Chronic Kidney Disease Prognosis Consortium reported that the use of the new eGFR creatinine-cystatin C equation had significantly greater discrimination of risk of kidney failure with replacement therapy compared to creatinine only based eGFR equations, supporting the Task Force recommendations to increase cystatin testing.7


Limitations

Cystatin C has not been shown to be affected by factors such as muscle mass and nutrition, factors which have been demonstrated to affect creatinine values. In addition, a rise in creatinine does not become evident until the GFR has fallen by approximately 50%.


Methodology

Creatinine: kinetic jafffe; Cystatin C: immunologic


Footnotes

1. Alfego D, Ennis J, Gillespie B, et al. Chronic Kidney Disease Testing Among At-Risk Adults in the U.S. Remains Low: Real-World Evidence From a National Laboratory Database. Diabetes Care. 2021 Sep;44(9):2025-2032.34353883
2. National Kidney Foundation, CKDintercept. Estimated Glomerular Filtration Rate (eGFR) - summary flyer (02-10-8361_ICB); 2021.
3. Katayev A, Zebelman AM, Sharp TM, Flynn S, Bernstein RK. Prevalence of isolated non-albumin proteinuria in the US population tested for both, urine total protein and urine albumin: An unexpected discovery. Clin Biochem. 2017 Apr;50(6):262-269.27916507
4. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International Supplements. 2013;3:1-150. Accessed at https://kdigo.org/wp-content/uploads/2017/02/KDIGO_2012_CKD_GL.pdf.
5. Delgado C, Baweja M, Crews DC, et al. A Unifying Approach for GFR Estimation: Recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. Am J Kidney Dis. 2022 Feb;79(2)268-288.e1.34563581
6. Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021 Nov 4;385(19)1737-1749.34554658
7. Gutiérrez OM, Sang Y, Grams ME, et al. Association of Estimated GFR Calculated Using Race-Free Equations With Kidney Failure and Mortality by Black vs Non-Black Race. JAMA. 2022 Jun 21;327(23)2306-2316.35667006

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