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Test code(s) 39165

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

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

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

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


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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.

Reference

  1. 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.
  2. 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
  3. 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
  4. What is Hyperkalemia? National Kidney Foundation. Reviewed February 8, 2016. Accessed July 29, 2021. https://www.kidney.org/atoz/content/what-hyperkalemia
  5. 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
  6. 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
  7. 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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