Renal Emergencies
Jennifer Thull-Freedman
Introduction
Most common cause of acute renal failure in children is prerenal
Common to find varying degrees of functional/transient proteinuria or hematuria
Proteinuria
Common Causes of Isolated Proteinuria
Functional/transient proteinuria
Caused by fever, exercise, dehydration, seizures, exposure to cold, congestive heart failure
Urine dip usually < 2+ proteinuria (< 100 mg/dL)
Benign postural (orthostatic) proteinuria
Usually occurs after 7 years of age
Urine protein: creatinine ratio in a first morning void is normal
Glomerulopathy
Nephrotic syndrome (see below)
Tubular
Overload proteinuria
Tubular dysfunction (reflux nephropathy, ischemic injury, cystinosis)
Benign persistent proteinuria
Laboratory Evaluation
Dipstick:
False positive with concentrated urine, pH > 8, gross hematuria or pyuria
False negative with very dilute, acidic urine (pH < 4.5)
Urine protein: creatinine ratio (mg/mg)
< 0.5 if < 2 years age or < 0.2 for older children considered normal
> 1 suspicious for nephrotic range proteinuria
> 2 suggestive of nephrotic range proteinuria
Consider 12-24 hour collection if urine protein:creatine ratio is abnormal
Additional evaluation to consider: electrolytes, urea, creatinine, albumin, cholesterol, C3, C4, ANA, CBC, VBG
Nephrotic Syndrome
Clinical syndrome of proteinuria due to loss of glomerular membrane selectivity
Characterized by proteinuria, hypoproteinemia, edema, hyperlipidemia
Secondary disturbances: hypocalcemia (due to hypoalbuminemia), hyperkalemia (due to prerenal azotemia), hyponatremia, hypercoagulability, hypogammaglobulinemia
Epidemiology
Primary acquired form (idiopathic minimal-change nephrosis) most common from 18 months to 6 years of age; 80% of cases
Secondary acquired form most common > 6 years; causes include infection, drugs, systemic disease (HUS, HSP, SLE, sickle cell, etc.)
Diagnosis
Hypoalbuminemia < 3.0 g/dL
Urine protein 100-300 mg/dL or > 40 mg/m2/hour in 24-hour period
Treatment for New-Onset Disease
Prednisone 2 mg/kg/day for 4-6 weeks, then taper
Anticipate response in 7-10 days
Furosemide may be considered (1-2 mg/kg/day)
Albumin infusion if needed to emergently increase oncotic pressure
Indications: symptomatic hypovolemia, peritonitis, clinically significant edema
1 g/kg of 25% solution over 4 hours with furosemide midway through transfusion
Watch for pulmonary edema
Optimize dietary protein
Complications
Infection: peritonitis, cellulitis, sepsis, meningitis
Thrombosis and thromboembolism: caution with femoral venous access
Other: ascites, pleural effusion, intravascular hypovolemia (shock, prerenal acute renal failure)
Hematuria
> 5-10 RBCs per high-power field from a centrifuged voided urine sample
Confirm with microscopy: RBCs, hemoglobin, myoglobin give positive dipstick
False positive dipstick can result from drugs (ascorbic acid, sulfonamides, iron sorbitol, metronidazole, nitrofurantoin); beets, dyes, drugs; urate crystals may discolor urine
False negative microscopy may occur in setting of low specific gravity causing cell lysis
