What are the guidelines for Chronic Kidney Disease (CKD) staging based on Impaired Renal Function?

From the Guidelines

Chronic kidney disease (CKD) is staged according to the presence of kidney damage and level of kidney function, with five stages defined by the estimated glomerular filtration rate (eGFR) as follows: Stage 1 (eGFR ≥90 mL/min/1.73m²), Stage 2 (eGFR 60-89 mL/min/1.73m²), Stage 3 (eGFR 30-59 mL/min/1.73m²), Stage 4 (eGFR 15-29 mL/min/1.73m²), and Stage 5 (eGFR <15 mL/min/1.73m² or dialysis) 1. The staging of CKD is crucial for guiding treatment decisions and predicting outcomes.

• The eGFR is a key parameter in staging CKD, and it should be calculated using standardized creatinine measurements and validated equations.
• The presence of kidney damage, such as proteinuria or structural changes on biopsy, is also an important factor in diagnosing CKD.
• The guidelines recommend that treatment of comorbid conditions, interventions to slow progression of kidney disease, and measures to reduce the risk for cardiovascular disease (CVD) should begin during stage 1 and stage 2 1.
• Evaluation and treatment of other complications of decreased GFR, such as anemia, malnutrition, bone disease, neuropathy, and decreased quality of life, should be undertaken during stage 3, as the prevalence of these complications begins to rise when GFR declines to less than 60 mL/min per 1.73 m2 1.
• Preparation for kidney replacement therapy should begin during stage 4, well before the stage of kidney failure.
• The clinical action plan for each stage should include actions begun in preceding stages.
• Patients with CKD should be referred to a specialist for consultation and comanagement if the patient's personal physician cannot adequately evaluate and treat the patient, particularly when GFR declines to less than 30 mL/min per 1.73 m2 1.

From the Research

Chronic Kidney Disease Staging Guidelines

The guidelines for chronic kidney disease (CKD) staging are based on the estimated glomerular filtration rate (GFR) and the degree of proteinuria.

• CKD is defined as a GFR less than 60 mL/min/1.73 m2 or persistent evidence of kidney damage on imaging, biopsy, or urinalysis that persists for longer than 3 months 2.
• The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is the most accurate creatinine-based method for estimating GFR in routine practice 2.
• Cystatin C level measurement can be considered if patients have factors that might make creatinine-based equations inaccurate (eg, high or low muscle mass) 2.

Classification of CKD

CKD is classified into stages based on estimated GFR, degree of proteinuria, and the cause.

• The best available indicator of overall kidney function is GFR, which is measured either via exogenous markers (eg, DTPA, iohexol), or estimated using equations 3.
• Presence of proteinuria is associated with increased risk of progression of CKD and death 3.
• Kidney biopsy samples can show definitive evidence of CKD, through common changes such as glomerular sclerosis, tubular atrophy, and interstitial fibrosis 3.

Estimating GFR

GFR can be estimated using serum markers such as serum creatinine (SCr) or cystatin C.

• The estimation of GFR by SCr differs in health and in chronic kidney disease (CKD) due to differences in GFR range and in creatinine production between these two populations 4.
• Validation is improved by refitting equation coefficients to compare populations, recognizing the asymmetry between estimated GFR and measured GFR, and using residual plots instead of Bland-Altman plots to assess bias 4.
• The error in the classification of CKD stages by formulas was extremely common, with misclassification averaging 50% for creatinine-based and 35% for cystatin C-based equations 5.