Chronic Kidney Disease

Excerpt

Chronic kidney disease (CKD) is characterized by the presence of kidney damage or an estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m², persisting for 3 months or more, irrespective of the cause. CKD is a state of progressive loss of kidney function, ultimately resulting in the need for renal replacement therapy, such as dialysis or transplantation. Kidney damage refers to pathologic abnormalities suggested by imaging studies or renal biopsy, abnormalities in urinary sediment, or increased urinary albumin excretion rates.

The 2012 Kidney Disease Improving Global Outcomes (KDIGO) CKD classification recommends specifying the cause of CKD and classifies the condition into 6 categories based on GFR (G1 to G5, with G3 split into 3a and 3b). In addition, it also includes staging based on 3 levels of albuminuria (A1, A2, and A3), with each stage of CKD subcategorized according to the urinary albumin-creatinine ratio (ACR; mg/g or mg/mmol) in an early morning "spot" urine sample.

The 6 CKD categories, known as stages 1 through 5, are described below (stage 3 is separated into 3a and 3b):

1. G1: GFR 90 mL/min/1.73 m² and above with evidence of kidney disease, such as hematuria or proteinuria

2. G2: GFR 60 to 89 mL/min/1.73 m²

3. G3a: GFR 45 to 59 mL/min/1.73 m²

4. G3b: GFR 30 to 44 mL/min/1.73 m²

5. G4: GFR 15 to 29 mL/min/1.73 m²

6. G5: GFR less than 15 mL/min/1.73 m² or treatment by dialysis

The 3 levels of albuminuria include an ACR:

1. A1: ACR less than 30 mg/g (<3.4 mg/mmol)

2. A2: ACR 30 to 299 mg/g (3.4-34 mg/mmol)

3. A3: ACR greater than 300 mg/g (>34 mg/mmol)

The improved classification of CKD has been beneficial in identifying prognostic indicators related to decreased kidney function and increased albuminuria. However, a downside of this classification system is the potential for overdiagnosis of CKD, particularly in older individuals.