CKD Definition
Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function present for ≥3 months, with implications for health. 1
Diagnostic Criteria
CKD is diagnosed when either of the following persists for ≥3 months 2, 3:
1. Kidney Damage (with or without decreased GFR)
Manifested by one or more markers:
- Albuminuria: Albumin-to-creatinine ratio (ACR) ≥30 mg/g 3
- Sex-specific cutpoints: >17 mg/g in men, >25 mg/g in women 3
- Urine sediment abnormalities
- Electrolyte/tubular disorders
- Structural abnormalities on imaging
- Pathological abnormalities on biopsy
- History of kidney transplantation 1
2. Decreased Kidney Function
Key Measurement Details
GFR Assessment:
- GFR <60 mL/min/1.73 m² represents loss of half or more of normal adult kidney function 3
- Should be estimated using prediction equations (MDRD Study equation or Cockcroft-Gault), not serum creatinine alone 4
- Normal GFR in young adults: approximately 120-130 mL/min/1.73 m² 3
- GFR declines with age but decreased GFR remains an independent predictor of adverse outcomes even in elderly 3
Albuminuria Categories: 1
- A1: <30 mg/g (normal to mildly increased)
- A2: 30-300 mg/g (moderately increased)
- A3: >300 mg/g (severely increased)
Critical Temporal Component
The 3-month duration requirement is essential to distinguish CKD from acute kidney injury (AKI) or acute kidney diseases and disorders (AKD) 1, 5. This persistence criterion ensures the diagnosis reflects chronic, not reversible, kidney pathology.
Clinical Implications
Why this definition matters for patient outcomes:
- Below GFR 60 mL/min/1.73 m², prevalence of complications (hypertension, anemia, malnutrition, bone disease) increases significantly 3
- CKD patients have higher risk of cardiovascular disease and death than progression to kidney failure 3
- Early detection enables interventions to slow progression and prevent complications 3
Common Pitfall
Do not rely on serum creatinine alone - it grossly overestimates kidney function, as patients can maintain seemingly normal creatinine levels (e.g., 1.3 mg/dL) despite declining GFR 4. Always use estimating equations that incorporate age, sex, and race.