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Cystatin C with Glomerular Filtration Rate, Estimated (eGFR)

Cystatin C with Glomerular Filtration Rate, Estimated (eGFR)

Test Summary

Cystatin C with Glomerular Filtration Rate, Estimated (eGFR)

  

Clinical Use

  • Detect chronic kidney disease (CKD) in adults

  • Monitor CKD therapy and/or progression in adults

Clinical Background

About 30 million people in the United States are currently affected by CKD.1 Treatment at earlier stages is generally effective in preventing or delaying adverse outcomes.2 Monitoring patients who have CKD, or are at high risk for developing it, is therefore important for decreasing morbidity and mortality.2

CKD is defined by the Kidney Disease Improving Global Outcomes (KDIGO) 2012 international guideline as the presence of glomerular filtration rate (GFR) <60 mL/min/1.73 m2 for >3 months and/or evidence of kidney damage for >3 months.2 The guideline recommends creatinine-based eGFR (eGFRcreat) for initial assessment of GFR.2

However, creatinine levels are affected by diet and muscle mass.3,4 Therefore, creatinine-based eGFR may be imprecise in people who are obese, are suffering from muscle-wasting disease or malnutrition, or have a high- or low-meat diet. This is of particular concern in people with creatinine-based eGFR of <60 mL/min/1.73 m2, where misclassification of eGFR may lead to an incorrect diagnosis of CKD. Cystatin-based eGFR testing offers an alternative for these groups. Although small but significant associations of cystatin C levels with diabetes, obesity, and inflammation have been reported,4,5 cystatin-based eGFR is less influenced by diet and muscle mass and is therefore more appropriate for patients in whom creatinine-based results may be misleading.

Therefore, when eGFRcreat indicates mild to moderate CKD (45-59 mL/min/1.73 m2) in a patient without albuminuria, the guideline recommends using cystatin C-based eGFR (eGFRcys) or creatinine plus cystatin C-based eGFR (eGFRcreat-cys) to confirm CKD.2 An eGFRcys or eGFRcreat-cys of <60 mL/min/1.73 m2 confirms a diagnosis of CKD.2

Confidence in the use of cystatin C-based eGFR has increased since the 2012 KDIGO guideline was published; results of a large meta-analysis show that cystatin C-based eGFR detects increased risk of adverse outcomes that is not detected by creatinine-based eGFR.5,6

Individuals Suitable for Testing

  • Adults who are at risk of, or who have, CKD

Method

  • Particle-enhanced turbidimetric immunoassay (PETIA)

  • Analytical sensitivity: 0.25 mg/L

  • Reportable range: 0.25 mg/L-7.00 mg/L

The eGFR is calculated using cystatin C measurements calibrated to International Federation of Clinical Chemistry (IFCC) certified reference material, along with the patient's age and sex, according to the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI 2012) equation.3

Interpretive Information

The table below provides interpretation of specific eGFR values for prognosis of CKD.

Table. Prognosis of Chronic Kidney Disease Based on eGFR Values2,a

eGFR, mL/min/1.73 m2

Prognosis

≥90b

Normal

60-89b

Mild decrease

45-59

Mild to moderate decrease

30-44

Moderate to severe decrease

15-29

Severe decrease

<15

Kidney failure

eGFR, estimated glomerular filtration rate.

a

This table applies to creatinine-based and cystatin C-based eGFR.

b

The National Kidney Disease Education Program (NKDEP) recommends that actual values above 60 mL/min/1.73 m2 be reported only as >60 due to variability near the upper limit of the reference range.7

 

References

  1. Centers for Disease Control and Prevention. National chronic kidney disease fact sheet 2017. https://www.cdc.gov/diabetes/pubs/pdf/kidney_factsheet.pdf. Accessed July 7, 2017.

  2. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Inter Suppl. 2013;3:1-150. http://www.kdigo.org/clinical_practice_guidelines/pdf/CKD/KDIGO_2012_CKD_GL.pdf. Accessed July 10, 2017.

  3. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367:20-29.

  4. Stevens LA, Schmid CH, Greene T, et al. Factors other than glomerular filtration rate affect serum cystatin C levels. Kidney Int. 2009;75:652-660.

  5. Shlipak MG, Matsushita K, Ärnlöv J, et al. Cystatin C versus creatinine in determining risk based on kidney function. N Engl J Med. 2013;369:932-943.

  6. Inker LA, Astor BC, Fox CH, et al. KDOQI US commentary on the 2012 KDIGO clinical practice guideline for the evaluation and management of CKD. Am J Kidney Dis. 2014;63:713-735.

  7. Myers GL, Miller WG, Coresh J, et al. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clin Chem. 2006;52:5-18.
     

Content reviewed 08/2017

 
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