Kidney Profile

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.

Quest Diagnostics provides several current and referenced materials. The links are provided below:

Laboratory Testing for Chronic Kidney Disease Diagnosis and Management - Test Guide

Kidney Profile -Test Summary

Diabetes, Advancing Chronic Kidney Disease Management Panel - Test Summary

Cystatin C with Glomerular Filtration Rate, Estimated (eGFR) – Test Summary

Creatinine-Based Estimated Glomerular Filtration Rate (eGFR) - Test Summary