Diagnostic Indications of Chronic Kidney Disease
Chronic kidney disease is diagnosed when either kidney damage or decreased kidney function (GFR <60 mL/min/1.73 m²) persists for 3 or more months, regardless of the underlying cause. 1, 2
Two Primary Diagnostic Pathways
CKD can be identified through either of two distinct criteria that must persist for at least 3 months:
1. Evidence of Kidney Damage (at any GFR level)
Persistent proteinuria is the principal marker of kidney damage and serves as the primary indicator even when GFR remains normal. 1
Specific proteinuria thresholds:
- Albumin-creatinine ratio >30 mg/g in spot urine samples (general threshold) 1
- Sex-specific cutpoints: >17 mg/g in men and >25 mg/g in women 1
Additional markers of kidney damage include: 1
- Abnormalities in urine sediment
- Abnormalities in blood and urine chemistry measurements
- Abnormal findings on imaging studies (structural abnormalities)
- History of kidney transplantation 1
2. Decreased Kidney Function
GFR <60 mL/min/1.73 m² is diagnostic of CKD by itself when persistent for >3 months, even without other markers of kidney damage. 1 This threshold represents loss of half or more of normal adult kidney function, and below this level, the prevalence of CKD complications increases significantly. 1
Normal GFR reference values: 1
- Young adults: approximately 120-130 mL/min/1.73 m²
- Declines with age, but this decline remains an independent predictor of adverse outcomes including death and cardiovascular disease 1, 2
Screening Algorithm for High-Risk Populations
Annual screening is recommended for patients at increased risk, even with normal baseline kidney function: 1
High-risk groups requiring annual screening include: 1
- African American individuals
- Patients with diabetes
- Patients with hypertension
- Patients with hepatitis C virus coinfection
- HIV-infected patients with RNA levels ≥4,000 copies/mL or CD4+ counts <200 cells/mL
Screening tests consist of: 1
- Urine analysis for proteinuria/albuminuria
- Serum creatinine to estimate GFR or creatinine clearance
Critical Diagnostic Considerations
A common pitfall: GFR estimates >60 mL/min/1.73 m² are not reported as numeric values by clinical laboratories due to reduced accuracy of estimating equations at higher levels. 1 Therefore, patients with GFR ≥60 mL/min/1.73 m² require evidence of kidney damage (such as proteinuria or imaging abnormalities) to meet diagnostic criteria for CKD. 1, 3
Age-related decline should not be dismissed as "normal aging": The definition of CKD remains the same regardless of age, as decreased GFR in elderly patients independently predicts adverse outcomes including death, cardiovascular disease, and requires medication dose adjustments. 1, 2 Approximately 17% of persons older than 60 years have an estimated GFR <60 mL/min/1.73 m². 1
Staging After Diagnosis
Once CKD is diagnosed, staging is determined by GFR level regardless of the underlying diagnosis: 1
- Stage 1: GFR ≥90 mL/min/1.73 m² with kidney damage 2
- Stage 2: GFR 60-89 mL/min/1.73 m² with kidney damage 2
- Stage 3: GFR 30-59 mL/min/1.73 m² 2
- Stage 4: GFR 15-29 mL/min/1.73 m² 2
- Stage 5: GFR <15 mL/min/1.73 m² or kidney failure requiring dialysis 2
Albuminuria should be assessed alongside GFR for comprehensive risk stratification and management planning. 2, 4