CKD Staging and Diagnostic Criteria

Overall Staging Framework

• Chronic kidney disease is classified into five stages based on glomerular filtration rate (GFR); stages 1‑2 require documented kidney damage in addition to GFR thresholds, whereas stages 3‑5 are defined by GFR alone. 1

Diagnostic Requirements for Early Stages

• For stages 1 and 2, a GFR measurement alone is insufficient; clinicians must document kidney damage using markers such as albuminuria (albumin‑to‑creatinine ratio > 30 mg/g), proteinuria, abnormal urine sediment, pathologic findings, or imaging abnormalities. 2

GFR‑Based Diagnosis from Stage 3 Onward

• Beginning at stage 3 (GFR < 60 mL/min/1.73 m²), CKD can be diagnosed on the basis of GFR alone, irrespective of other damage markers. 2
• This GFR threshold corresponds to loss of ≥ 50 % of normal adult kidney function and marks the point at which CKD‑related complications increase markedly. 2, 3

Temporal Criteria

• All CKD diagnoses require that the abnormal GFR or kidney‑damage markers persist for ≥ 3 months; transient changes do not meet diagnostic criteria. 2, 4
• The ≥ 3‑month requirement distinguishes CKD from acute kidney injury (AKI) or acute kidney disease (AKD). 5

Stage 3 Subdivision

• Stage 3 is frequently subdivided for clinical decision‑making:
  
  • Stage 3a – GFR 45‑59 mL/min/1.73 m².
  • Stage 3b – GFR 30‑44 mL/min/1.73 m². 6

Stage 5 Initiation of Dialysis

• In the United States, approximately 98 % of patients start dialysis when GFR falls below 15 mL/min/1.73 m². 3
• Patients receiving dialysis are classified as “5D,” while transplant recipients are designated “5T” (or CKD G1T‑G5T) based on post‑transplant kidney function. 6

Terminology Recommendations

• The term “end‑stage renal disease” (ESRD) is an administrative label for Medicare billing and should be avoided in clinical documentation; preferred terms are “kidney failure” or “stage 5 CKD.” 3, 6

CKD Staging and Diagnostic Criteria

GFR‑Based Staging of Chronic Kidney Disease

• CKD is classified into five stages based on estimated GFR:

Diagnostic Requirements for CKD

• A diagnosis of CKD requires that structural or functional kidney abnormalities persist for ≥ 3 months; transient changes do not meet criteria. 8
• For Stages 1 and 2, a GFR above 60 mL/min/1.73 m² is insufficient on its own; documented kidney damage (e.g., proteinuria, albuminuria, hematuria, imaging or pathological abnormalities) must be present. 8
• Beginning with Stage 3 (GFR < 60 mL/min/1.73 m²), CKD can be diagnosed on the basis of GFR alone, irrespective of other markers of kidney injury. 9

Estimating GFR Accurately

• Reliable GFR estimation requires prediction equations that incorporate age, sex, race, and body size (e.g., MDRD or CKD‑EPI); reliance on serum creatinine alone markedly overestimates kidney function. 10

Clinical Implications of Advanced Stages

• Stage 4 signifies advanced kidney disease and prompts preparation for renal replacement therapy (e.g., planning for dialysis access or transplantation). 9
• Stage 5 denotes kidney failure; patients may require chronic dialysis even if the measured GFR is technically in the Stage 4 range when uremic symptoms are present. 8
• Patients on dialysis are classified as “5D”, whereas those who have received a kidney transplant are classified as “5T.” 11

CKD Staging, Diagnosis, and Management Guidelines

Classification and Stage Definitions

• CKD is classified into five stages based on estimated glomerular filtration rate (eGFR); stages 1‑2 require documented kidney damage (e.g., albuminuria ≥ 30 mg/g) in addition to eGFR thresholds, whereas stages 3‑5 are defined by eGFR alone. 12
• Stage 1: eGFR ≥ 90 mL/min/1.73 m² plus evidence of kidney damage such as proteinuria, abnormal imaging, or pathological findings. 12, 13
• Stage 2: eGFR 60‑89 mL/min/1.73 m² plus evidence of kidney damage. 12, 13
• Stage 3: eGFR 30‑59 mL/min/1.73 m² (with or without kidney damage). 12, 13
• Stage 4: eGFR 15‑29 mL/min/1.73 m². 12, 13
• Stage 5: eGFR < 15 mL/min/1.73 m² or requiring dialysis (kidney failure). 12, 13, 14

Diagnostic Criteria

• CKD diagnosis requires that the abnormality (eGFR reduction or markers of kidney damage) persist for ≥ 3 months to distinguish chronic disease from acute kidney injury. 12, 15
• For stages 1‑2, kidney damage must be documented using one or more of the following: albumin‑to‑creatinine ratio > 30 mg/g (sex‑specific cut‑points > 17 mg/g in men, > 25 mg/g in women), abnormal urine sediment, biopsy‑proven pathology, or structural abnormalities on imaging. 12, 13
• Beginning at stage 3 (eGFR < 60 mL/min/1.73 m²), CKD can be diagnosed on the basis of eGFR alone, regardless of other damage markers. This threshold reflects loss of ≥ 50 % of normal adult kidney function and coincides with a marked rise in complications such as anemia, malnutrition, bone disease, and neuropathy. 12, 16

Management Recommendations by Stage

• Stages 1‑2 – Prioritize identification of the underlying etiology, aggressive control of comorbid conditions (especially hypertension), implementation of measures to slow progression, and reduction of cardiovascular risk. 12, 16
• Stage 3 – Initiate evaluation and treatment of CKD‑related complications as their prevalence increases when eGFR falls below 60 mL/min/1.73 m²; refer to a nephrologist when eGFR drops below 30 mL/min/1.73 m² (stage 3b or worse). 12, 16
• Stage 4 – Begin preparation for kidney replacement therapy, including planning for dialysis access or transplant evaluation well before the onset of uremic symptoms. 12, 16
• Stage 5 – In the United States, approximately 98 % of patients commence dialysis when eGFR falls below 15 mL/min/1.73 m²; these patients are classified as “5D,” while transplant recipients are designated “5T.” 12

eGFR Estimation Methods

• Use prediction equations such as the MDRD Study or CKD‑EPI equations, which incorporate age, sex, race, and body size; reliance on serum creatinine alone substantially overestimates kidney function. 17
• The MDRD equation demonstrates a tighter correlation with measured GFR than 24‑hour creatinine clearance. 17

Albuminuria Assessment

• Confirm albuminuria with two of three urine specimens collected over a 3‑6 month interval to account for biological variability. 13

Terminology

• Avoid the administrative term “end‑stage renal disease” (ESRD) in clinical documentation; prefer “kidney failure” or “stage 5 CKD.” 12