Diagnostic Criteria for Chronic Kidney Disease
Chronic kidney disease (CKD) is defined as either kidney damage or decreased kidney function (glomerular filtration rate [GFR] <60 mL/min/1.73 m²) that persists for 3 or more months. 1
Definition Components
- Kidney damage is usually ascertained by markers rather than by kidney biopsy 1
- Persistent proteinuria is the principal marker of kidney damage 1
- An albumin-creatinine ratio >30 mg/g in untimed (spot) urine samples is considered abnormal; some studies suggest sex-specific cut points of >17 mg/g in men and >25 mg/g in women 1
- Other markers of kidney damage include abnormalities in urine sediment, blood and urine chemistry measurements, and abnormal findings on imaging studies 1
- GFR <60 mL/min/1.73 m² represents loss of half or more of the adult level of normal kidney function 1
GFR Estimation
- GFR is the best measure of overall kidney function in health and disease 1
- 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 (e.g., high or low muscle mass) 2
CKD Staging System
CKD is classified into five stages based on GFR level:
| GFR Category | CKD Stage | GFR (mL/min/1.73 m²) | Description |
|---|---|---|---|
| G1 | 1 | ≥90 | Normal or high (with evidence of kidney damage) |
| G2 | 2 | 60-89 | Mildly decreased (with evidence of kidney damage) |
| G3a | 3 | 45-59 | Mildly to moderately decreased |
| G3b | 3 | 30-44 | Moderately to severely decreased |
| G4 | 4 | 15-29 | Severely decreased |
| G5 | 5 | <15 | Kidney failure (may require renal replacement therapy) |
| [1,3] |
Proteinuria Assessment
- The ratio of protein or albumin to creatinine in an untimed urine sample is an accurate estimate of protein or albumin excretion rate 1
- For adults at increased risk for CKD (e.g., those with diabetes, hypertension):
- Persistent proteinuria is defined as two or more positive results on quantitative tests temporally spaced over 3 months 1
Additional Diagnostic Criteria
- Kidney damage can be confirmed by:
- Excessive albuminuria (albumin excretion rate ≥30 mg/24h; albumin-creatinine ratio ≥30 mg/g) 1
- Urine sediment abnormalities 1
- Electrolyte or other abnormalities caused by tubular disorders 1
- Abnormal histology on kidney biopsy 1
- Structural abnormalities detected by kidney imaging (e.g., small echogenic kidneys, dysplastic or polycystic kidneys, renal scarring, hydronephrosis) 1
Risk Factors and Screening
- Screening should be considered for patients at high risk of CKD: those with diabetes, hypertension, cardiovascular disease, or family history of kidney failure 2
- Screening typically involves:
Clinical Implications
- CKD is associated with increased risk of complications including hypertension, anemia, malnutrition, bone disease, neuropathy, and decreased quality of life 1
- Decreased GFR in elderly patients is an independent predictor of adverse outcomes such as death and cardiovascular disease 1
- Patients with CKD should be considered in the highest-risk group for subsequent cardiovascular disease events 1
- Early detection and treatment can prevent or delay adverse outcomes of CKD, including loss of kidney function and development of kidney failure 1, 3
Common Pitfalls in Diagnosis
- Relying solely on serum creatinine without calculating estimated GFR can miss early CKD 1
- Failing to repeat abnormal tests over 3 months to confirm persistence of findings 1, 3
- Not considering age-related decline in GFR (normal GFR declines with age, but decreased GFR in elderly still predicts adverse outcomes) 1
- Overlooking proteinuria in patients with normal GFR (these patients are still at increased risk for adverse outcomes) 1