Diagnostic Criteria and Indications for Chronic Kidney Disease
Core Definition
CKD is diagnosed when abnormalities of kidney structure or function persist for more than 3 months with implications for health. 1 This requires either a GFR <60 mL/min/1.73 m² OR evidence of kidney damage at any GFR level, sustained for at least 3 months. 1, 2, 3
Two Pathways to Diagnosis
Pathway 1: Reduced GFR Alone
- GFR <60 mL/min/1.73 m² persisting >3 months is diagnostic by itself, even without other markers of kidney damage. 4, 2
- This threshold represents loss of more than half of normal adult kidney function (normal is ~125 mL/min/1.73 m²). 1
- The 3-month persistence requirement is mandatory—transient decreases do not qualify as CKD. 3
Pathway 2: Evidence of Kidney Damage at Any GFR
- Albuminuria (ACR ≥30 mg/g) is the principal marker of kidney damage and can diagnose CKD even when GFR is ≥60 mL/min/1.73 m². 1, 4, 2
- Sex-specific cutpoints: >17 mg/g in men and >25 mg/g in women. 1, 4
- Other markers include: abnormalities on kidney biopsy, abnormal urine sediment, blood/urine chemistry abnormalities, or abnormal imaging findings. 1, 3
GFR Estimation Requirements
Use the CKD-EPI creatinine equation for estimating GFR—it has less bias than the older MDRD equation, especially at GFR ≥60 mL/min/1.73 m². 1, 4, 2
Critical Confirmation Step
- For patients with eGFR 45-59 mL/min/1.73 m² (stage G3a) WITHOUT albuminuria or other damage markers, measure cystatin C to confirm the diagnosis. 4, 2
- This group represents 41% of persons in the U.S. estimated to have CKD based on creatinine alone, making confirmation essential to avoid overdiagnosis. 4
- Two-thirds of persons with eGFR <60 by creatinine have CKD confirmed by cystatin C <60. 2
Classification System (CGA)
CKD must be classified by Cause, GFR category, and Albuminuria category. 1
GFR Categories:
- G1: ≥90 mL/min/1.73 m² (requires evidence of kidney damage for CKD diagnosis) 2
- G2: 60-89 mL/min/1.73 m² (requires evidence of kidney damage for CKD diagnosis) 2, 3
- G3a: 45-59 mL/min/1.73 m² 1, 2
- G3b: 30-44 mL/min/1.73 m² 1, 2
- G4: 15-29 mL/min/1.73 m² 2
- G5: <15 mL/min/1.73 m² 2
Albuminuria Categories:
- A1: <30 mg/g (normal to mildly increased) 2
- A2: 30-300 mg/g (moderately increased) 2
- A3: >300 mg/g (severely increased) 2
Key Diagnostic Pitfalls to Avoid
Do NOT diagnose CKD if:
- eGFR is ≥60 mL/min/1.73 m² without documented markers of kidney damage. 4 A GFR of 88 mL/min/1.73 m² without evidence of kidney damage does not constitute CKD. 3
- Abnormalities have not persisted for 3 months—single measurements are insufficient. 1, 3
Do NOT use:
- Creatinine clearance or estimated creatinine clearance—these overestimate GFR and lead to misclassification. 4, 5
- The term "microalbuminuria" in laboratory reporting—use ACR values instead. 4
Laboratory Reporting Standards
- Laboratories should report ACR and protein-to-creatinine ratio in untimed (spot) urine samples, not just concentrations alone. 4
- eGFR should be automatically reported alongside creatinine to facilitate interpretation. 2
- Creatinine assays must be calibrated to isotope-dilution mass spectrometry reference standards. 1, 2
Screening Indications
Annual screening is recommended for high-risk groups, including: 3
- Patients with diabetes mellitus 3, 6
- Patients with hypertension 3, 6
- African American individuals 3
- Patients with cardiovascular disease 6
- Family history of kidney disease 6, 7
- Previous acute kidney injury 6, 7
- Age ≥60 years 7
Clinical Implications
- GFR <60 mL/min/1.73 m² is associated with increased risk for drug toxicity, endocrine/metabolic complications, cardiovascular disease, and death, regardless of age or cause. 1
- ACR ≥30 mg/g (>3 times normal) is associated with increased risk for CKD complications. 1
- The subdivision of G3 into G3a and G3b is critical because these categories have different outcomes and risk profiles. 1, 2
- Decreased GFR in elderly patients is an independent predictor of adverse outcomes and requires drug dosage adjustments, just as in younger patients. 1