Chronic kidney disease

From IDWiki

Background

Definition

  • Structural or functional kidney disorder lasting at least [3 months]

KDIGO Classification

  • Defined as 3 or more months of either GFR < 60 or 1 or more marker of kidney damage:
    • Proteinuria
    • Urine sediments
    • Tubular electrolyte disorder
    • Kidney transplant
    • Structural disease
  • Categories & grades:
    • Grade 1: GFR ≥90 (normal) with a marker of kidney disease
    • Grade 2: GFR 60-89 with a marker of kidney disease
    • Grade 3a: GFR 45-59
    • Grade 3b: GFR 30-44
    • Grade 4: GFR 15-29
    • Grade 5: GFR <15, ESRD

Epidemiology

  • 8% of population have GFR < 60
  • 4% of population have proteinuria despite normal GFR

Differential Diagnosis

  • Diabetes
  • Cardiovascular disease/HTN
    • Ischemic nephropathy
    • Nephrosclerosis
  • Glomerulonephritis
  • PCKD
  • Drugs, especially lithium, cyclosporine, tacrolimus, tenofivir
  • Other disease associations
    • Inflammatory bowel disease: oxalate nephropathy
    • Rheumatoid arthritis: amyloidosis
    • Cirrhosis: Type 2 hepatorenal syndrome
    • Solid tumours: membranous nephropathy
    • Severe CHF: cardiorenal syndrome
    • Post-AKI: incomplete recovery of ATN in hospital

Investigations

Laboratory

  • GFR
    • MDRD underestimates the GFR in healthy patients
    • CKD-Epi is the newer equation and possibly more accurate
    • Radioisotopic GFR is the gold standard, inulin clearance is the gold standard for research
    • Cystatin C may complement or replace creatinine in the future
  • Urinalysis, though "protein" only picks up albumin
  • Urine ACR and PCR

Imaging

  • Abdominal ultrasound

Management

  • Education re: dialysis and transplant
  • Refer to nephrology when:
    • GFR drops by 5+ per year
    • Acute on chronic kidney injury
    • eGFR < 30 (Stage 4)
    • Proteinuria >1g/day
    • Difficulty controlling BP
  • BP control
    • ACEi + CCB + diuretic
    • If albuminuria, target <130/80, else <140/90
  • Proteinuria
    • If proteinuria >500mg/d or ACR>30mg/mmol, start ACEi/ARB regardless of BP
    • If diabetes and microalbuminuria, start ACEi/ARB
  • Metabolic acidosis (normal anion gap)
    • Oral sodium bicarbonate 0.5-1 mEq/kg/d to maintain bicarb between 23-29 mmol/L
  • Avoid nephrotoxic mediation like NSAIDs

Initial Investigations

  • Urinalysis to help diagnose glomerulonephritis or AIN
  • ACR, a component of the KFRE score
  • Urea, to help rule out volume depletion
  • Urine electrolytes, with low urine Na (FENA<1%) suggesting volume depletion
  • Ultrasound of the kidneys to assess for structural kidney disease and renal stones, plus or minus arterial Dopplers if suspecting renovascular disease
  • Serum protein electrophoresis
  • 24-hour urine protein and urine electrophoresis, if urine ACR >300 mg/mmol (<3 g/d)
  • CK, to rule out rhabdomyolysis
  • ANCAs, if UA shows blood and protein and there's a rapid decline in kidney function
  • CBC with blood film, looking for evidence of a TMA

Routine Investigations

  • Annually for patients with stage 2 or higher: creatinine, Na/K/Cl/CO2, ACR
  • Every 3-6 months for patients with stage 4 or higher:
    • Na/K/Cl/CO2, creatinine, urea
    • Ca/Mg/PO4/albumin/PTH
    • ACR
    • CBC, ferritin, transferrin saturation

Sick Day Medications

  • Some medications should be held during an acute illness, before surgery, or with IV contrast
  • Includes ACEi, ARB, aldosterone antagonists, SGLT-2 inhibitors, diuretics, NSAIDs, metformin, sulfonylureas, and direct renin inhibitors
  • Hold ACEi/ARB when planning pregnancy

Complications

  • Anemia: treat iron deficiency before adding Epo, targetting 105-115
  • Hypocalcemia: give calcium between meals or rocaltrol (if the hyperphosphatemia is treated)
  • Hyperphosphatemia: give a phosphate binder like calcium or Renagel with meals
  • Metabolic bone disease: maintain normal phosphate with diet, binders, and vitamin D
  • Acidosis: supplement bicarb when < 22
  • Hyperkalemia from poor GFR, ACEi, DM
  • Pruritis: moisturizers, steroids, antihistamines

Prognosis

  • GFR declines linearly over time
  • Progression predicted by
    • Previous rate of progression
    • Hypertension **
    • Proteinuria **
    • Metabolic acidosis
  • High risk of cardiovascular mortality compared to general population
    • 30 year olds on dialysis have same risk as 80 year olds in the general population
    • Risk increases with a decreasing GFR

Further Reading

  • An approach to treating older adults with chronic kidney disease. CMAJ. 2023;195(17):E612-E618. doi: 10.1503/cmaj.221427