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Test code(s) 39165


Components:
Creatinine, Serum (test code 375)
Albumin, Random Urine with Creatinine (test code 6517)


Question 1. What is the laboratory definition of chronic kidney disease?

Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function, present for >3 months, withimplications for health.1 CKD can be diagnosed based on a glomerular filtration rate (GFR) <60 mL/min/1.73 m2 for >3 months, evidence of kidney damage for >3 months, or both.1

GFR is considered the best overall laboratory marker of kidney function.1 Because direct measurement of GFR can be problematic, an estimated GFR (eGFR) determined using creatinine- or cystatin C-based measurements is most commonly used to diagnose CKD in clinical practice. The Kidney Profile (test code 39165) incorporates creatinine-based eGFR.

Indications of kidney damage include a histologic abnormality, structural abnormality, history of kidney transplantation, abnormal urine sediment, tubular disorder-caused electrolyte abnormality, or an increased urinary albumin level (albuminuria). A urine albumin-creatinine ratio ≥30 mg/g (μg/mg) is considered evidence of albuminuria consistent with kidney damage.

Note that terminology has standardized to define a urine albumin-creatinine ratio result of ≥30 mg/g (albumin excretion rate ≥30 mg/24 h) as evidence of albuminuria; formerly, a ratio of 30-300 mg/g was referred to as “microalbuminuria,” and a ratio of >300 mg/g was defined as “macroalbuminuria.”1


Question 2. How are the eGFR and urine albumin-creatinine ratio used to manage patients?

KDIGO guidelines1 incorporate a risk map to

    Stage CKD

    Guide frequency of CKD monitoring

    Identify conditions that would necessitate a cystatin C-based eGFR

    Refer the patient to a nephrologist

Figure 1 provides an overview of recommended monitoring frequency for patients with CKD, based on risk of disease progression as assessed using eGFR and urine albumin-creatinine ratio. TestDirectory.QuestDiagnostics.com/HCP/IntGuide/DocLinks/TG_CKD_Fig1.pdf


Question 3. How does staging help to inform patient management?

The table below summarizes evidence-based suggestions for laboratory testing for complications and comorbidities in patients with CKD.


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Question 4. When is cystatin C-based eGFR indicated?

Being less influenced by diet and muscle mass, cystatin C-based eGFR testing is appropriate for patients in whom creatinine-based results may be misleading. These patients include pregnant people; persons with acute illness or suffering from malnutrition, serious comorbidities, or extremes of muscle mass (eg, bodybuilders, amputees, paraplegics, sufferers of a muscle-wasting disease or a neuromuscular disorder); or those taking creatine dietary supplements, or with a vegetarian or low-meat diet.1,5

However, cystatin C-based eGFR may be more affected by some non-GFR determinants, such as thyroid disorders, corticosteroid use, and smoking.3 In addition, small but significant associations of cystatin C levels with diabetes, obesity, and inflammation have been reported.6,7 For these reasons, creatinine-based eGFR is recommended for patients without contraindications.



References

    Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int Suppl. 2013;3(1):1-150.

    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(1):5-18. doi:10.1373/clinchem.2005.0525144

    Vassalotti JA, Centor R, Turner BJ, et al. Practical approach to detection and management of chronic kidney disease for the primary care clinician. Am J Med. 2016;129(2):153-162.e7 doi:10.1016/j.amjmed.2015.08.025

    What is Hyperkalemia? National Kidney Foundation. Reviewed February 8, 2016. Accessed July 29, 2021. https://www.kidney.org/atoz/content/what-hyperkalemia

    Levey AS, Coresh J, Tighiouart H, et al. Measured and estimated glomerular filtration rate: current status and future directions. Nat Rev Nephrol. 2020;16(1):51-64. doi:10.1038/s41581-019-0191-y

    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(10):932-943. doi:10.1056/NEJMoa1214234

    Stevens LA, Schmid CH, Greene T, et al. Factors other than glomerular filtration rate affect serum cystatin C levels. Kidney Int. 2009;75(6):652-660. doi:10.1038/ki.2008.638


This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

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Version 0: effective 09/14/2021 to present