Renal Emergencies
Jennifer Thull-Freedman
Introduction
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Most common cause of acute renal failure in children is prerenal
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Common to find varying degrees of functional/transient proteinuria or hematuria
Proteinuria
Common Causes of Isolated Proteinuria
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Functional/transient proteinuria
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Caused by fever, exercise, dehydration, seizures, exposure to cold, congestive heart failure
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Urine dip usually < 2+ proteinuria (< 100 mg/dL)
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Benign postural (orthostatic) proteinuria
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Usually occurs after 7 years of age
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Urine protein: creatinine ratio in a first morning void is normal
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Glomerulopathy
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Nephrotic syndrome (see below)
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Tubular
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Overload proteinuria
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Tubular dysfunction (reflux nephropathy, ischemic injury, cystinosis)
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Benign persistent proteinuria
Laboratory Evaluation
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Dipstick:
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False positive with concentrated urine, pH > 8, gross hematuria or pyuria
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False negative with very dilute, acidic urine (pH < 4.5)
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Urine protein: creatinine ratio (mg/mg)
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Consider 12-24 hour collection if urine protein:creatine ratio is abnormal
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Additional evaluation to consider: electrolytes, urea, creatinine, albumin, cholesterol, C3, C4, ANA, CBC, VBG
Nephrotic Syndrome
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Clinical syndrome of proteinuria due to loss of glomerular membrane selectivity
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Characterized by proteinuria, hypoproteinemia, edema, hyperlipidemia
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Secondary disturbances: hypocalcemia (due to hypoalbuminemia), hyperkalemia (due to prerenal azotemia), hyponatremia, hypercoagulability, hypogammaglobulinemia
Epidemiology
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Primary acquired form (idiopathic minimal-change nephrosis) most common from 18 months to 6 years of age; 80% of cases
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Secondary acquired form most common > 6 years; causes include infection, drugs, systemic disease (HUS, HSP, SLE, sickle cell, etc.)
Diagnosis
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Hypoalbuminemia < 3.0 g/dL
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Urine protein 100-300 mg/dL or > 40 mg/m2/hour in 24-hour period
Treatment for New-Onset Disease
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Prednisone 2 mg/kg/day for 4-6 weeks, then taper
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Anticipate response in 7-10 days
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Furosemide may be considered (1-2 mg/kg/day)
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Albumin infusion if needed to emergently increase oncotic pressure
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Optimize dietary protein
Complications
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Infection: peritonitis, cellulitis, sepsis, meningitis
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Thrombosis and thromboembolism: caution with femoral venous access
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Other: ascites, pleural effusion, intravascular hypovolemia (shock, prerenal acute renal failure)
Hematuria
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> 5-10 RBCs per high-power field from a centrifuged voided urine sample
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Confirm with microscopy: RBCs, hemoglobin, myoglobin give positive dipstick
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False positive dipstick can result from drugs (ascorbic acid, sulfonamides, iron sorbitol, metronidazole, nitrofurantoin); beets, dyes, drugs; urate crystals may discolor urine
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False negative microscopy may occur in setting of low specific gravity causing cell lysis

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