What is the glomerular filtration rate (GFR) for Stage 1 Chronic Kidney Disease (CKD)?

Stage 1 CKD: Definition by Glomerular Filtration Rate (GFR)

Stage 1 Chronic Kidney Disease (CKD) is defined as kidney damage with a normal or increased glomerular filtration rate (GFR) of ≥90 mL/min/1.73 m².

Definition and Classification

• Stage 1 CKD requires two components: a GFR ≥90 mL/min/1.73 m² AND evidence of kidney damage 1
• Kidney damage must be present for at least 3 months and can be identified through:
  • Albuminuria (albumin-to-creatinine ratio >30 mg/g in two of three spot urine specimens) 2
  • Proteinuria 1
  • Hematuria 1
  • Pathological abnormalities on kidney biopsy 1
  • Abnormalities in imaging tests 1

CKD Staging System

The current CKD classification system divides kidney disease into five stages based on GFR:

• Stage 1: GFR ≥90 mL/min/1.73 m² with evidence of kidney damage 1
• Stage 2: GFR 60-89 mL/min/1.73 m² with evidence of kidney damage 1
• Stage 3: GFR 30-59 mL/min/1.73 m² (moderate decrease in GFR) 1
• Stage 4: GFR 15-29 mL/min/1.73 m² (severe decrease in GFR) 1
• Stage 5: GFR <15 mL/min/1.73 m² (kidney failure) 1

Important Clinical Considerations

• The diagnosis of CKD requires the presence of abnormalities for at least 3 months to differentiate from acute kidney injury 1, 2
• For Stages 1 and 2, evidence of kidney damage must be present in addition to the GFR criteria 1
• For Stages 3-5, the GFR criteria alone are sufficient for diagnosis, regardless of evidence of kidney damage 1
• GFR is typically estimated using equations such as the MDRD (Modification of Diet in Renal Disease) or CKD-EPI equations rather than directly measured 3

Clinical Implications

• Even Stage 1 CKD with normal GFR carries increased risk for cardiovascular disease and mortality 1, 4
• Early detection of CKD at Stage 1 allows for interventions that may slow progression to more advanced stages 1
• Patients with Stage 1 CKD should be monitored for progression and managed for modifiable risk factors 1
• The choice of GFR estimation equation can significantly affect the prevalence estimates of CKD, particularly in early stages 5

Common Pitfalls and Caveats

• Relying solely on serum creatinine without calculating estimated GFR can lead to missed diagnoses, especially in elderly patients or those with reduced muscle mass 1, 3
• GFR estimating equations may underestimate true GFR in patients with normal kidney function or hyperfiltration 6
• Temporary fluctuations in kidney function markers do not constitute CKD unless they persist for at least 3 months 2
• Different GFR estimation equations may yield different results, potentially affecting CKD staging and prevalence estimates 5