Definition (Am J Kid Dis 2002;39:S1)
- GFR <60mL/min/1.73m2 for ≥3mo, ± kidney damage; irrespective of type of kidney disease
- Kidney damage for ≥3mo, defined by structural or functional abnormalities, ± ↓ GFR, manifested by pathological abnormalities OR markers of kidney damage → abnormalities in composition of blood or urine (e.g., proteinuria, hematuria), or abnormalities in imaging tests
- Affects approximately 10–16% of adults worldwide (NephSAP 2011;10:429)
- Causes: HTN, DM, glomerular diseases, vascular diseases, tubulointerstitial diseases, cystic diseases & diseases in allograft following transplantation; DM leading cause of CKD & kidney failure; HTN & glomerular diseases 2nd & 3rd most common causes of kidney failure (Am J Kid Dis 2002;39:S1)
- Evaluation, diagnosis, & classification: evaluate CKD patients to determine cause, severity, complications, comorbid conditions, risk for further loss of kidney function, CVD risk (Am J Kid Dis 2002;39:S1)
- Estimating glomerular filtration rate (GFR)
- Serum creatinine (SCr) should not be used alone to assess kidney function
- Estimates of GFR using SCr may be unreliable due to (1) day-to-day variations in creatinine excretion; (2) differences in generation of SCr due to age, gender, race; (3) unusually large or small muscle mass (e.g., athletes, malnourished individuals, elderly, immobilized patients); (4) diet [i.e., dietary creatine intake unusually high (e.g., creatine supplements) or low (e.g., vegetarians)]; (5) medications (e.g., cimetidine & trimethoprim inhibit secretion of SCr; cefoxitin directly interferes with SCr measurements); (6) laboratory analytical methods for measuring SCr
- MDRD & Cockcroft-Gault equations provide useful estimates of GFR in adults:
- MDRD: GFR (mL/min/1.73m2 = 186 × SCr−1.154 × age−0.203 × (0.742 if female) × (1.21 if AA)
- Cockcroft-Gault: CrCl (mL/min) = [(140 – age) × IBW]/[SCr × 72] × (0.85 if female)
- Assessing for proteinuria or albuminuria: 1st morning urine specimen preferred; correlates best with 24h protein excretion; when screening adults at ↑ risk for CKD, measure albumin in spot urine sample using either albumin-specific dipstick or albumin:creatinine ratio
- Prognosis → ↑ risk for end-stage renal disease (ESRD), CVD & mortality
- Signs & symptoms: metabolic acidosis, electrolyte abnormalities (↑ K+, ↑ Phos), fluid overload, uncontrolled HTN, uremic symptoms (e.g., nausea/vomiting, anorexia, weight loss/signs of malnutrition, pruritus, confusion, asterixis, myoclonus, wrist or footdrop, seizures, pericarditis or pleuritis, bleeding)
Clinical Pearl 16-1
After age 20–30y, GFR decreases by approximately 0.5–1.0mL/min/1.73m2/y with substantial interindividual variation (NephSAP 2011;10:423).
Clinical Pearl 16-2
Creatinine clearance (CrCl) systematically overestimates GFR by approximately 10–40% in normal individuals, but is greater & more unpredictable in patients with CKD. MDRD equation provides useful estimate of GFR ≤90mL/min/1.73m2.
Clinical Pearl 16-3
Urine protein:creatinine & albumin:creatinine ratios provide accurate estimates of urinary protein & albumin excretion rate, & are not affected by hydration.