Clinical meaning
Chronic kidney disease is defined as kidney damage (albuminuria, structural abnormalities) or GFR <60 mL/min/1.73m² persisting for ≥3 months. The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation is preferred for eGFR calculation, using serum creatinine, age, sex, and (previously) race. KDIGO staging combines GFR categories (G1: ≥90, G2: 60-89, G3a: 45-59, G3b: 30-44, G4: 15-29, G5: <15) with albuminuria categories (A1: <30 mg/g, A2: 30-300 mg/g, A3: >300 mg/g) to create a risk matrix for progression. Albuminuria is the most sensitive early marker of diabetic nephropathy and an independent cardiovascular risk factor. Two abnormal values ≥3 months apart confirm the diagnosis and exclude acute kidney injury.
Diagnosis & workup
Diagnostics & workup: - Serum creatinine with eGFR calculation (CKD-EPI equation): two values ≥3 months apart showing eGFR <60 confirms CKD - Urine albumin-to-creatinine ratio (UACR): spot sample; A1 (<30) normal, A2 (30-300) moderately increased, A3 (>300) severely increased - Urinalysis: proteinuria, hematuria, casts (RBC casts = glomerulonephritis, WBC casts = pyelonephritis/interstitial nephritis, waxy casts = advanced CKD) - Renal ultrasound: kidney size (small echogenic kidneys = chronic scarring; large kidneys = diabetic nephropathy, PKD, amyloidosis), hydronephrosis, cysts - Serum cystatin C: alternative to creatinine for eGFR; less affected by muscle mass, useful in elderly and extreme body habitus - BMP: electrolytes (hyperkalemia, hyperphosphatemia, metabolic acidosis), calcium - CBC: normocytic anemia from decreased erythropoietin production - Renal biopsy: for unexplained CKD, nephrotic syndrome, rapidly progressive GN, or when diagnosis impacts management