The sudden onset of dependent pitting edema or ascites is the most common presentation for children with NS. Anorexia, malaise, and abdominal pain are often present. Blood pressure may be elevated in up to 25% of children on presentation; acute tubular necrosis and significant hypotension may occur with sudden decline in serum albumin and significant volume depletion. Diarrhea (intestinal edema) and respiratory distress (pulmonary edema or pleural effusion) may be present. Typical MCNS is characterized by the absence of gross hematuria, renal insufficiency, hypertension (HTN), and hypocomplementemia.
Proteinuria of 1+ or higher on 2 to 3 random urine specimens suggests persistent proteinuria that should be further quantified. A UPr/Cr >0.2 on a first morning specimen excludes orthostatic proteinuria. UPr/Cr >2.0 indicates nephrotic range proteinuria.
In addition to a demonstration of proteinuria, hypercholesterolemia, and hypoalbuminemia, routine testing typically includes a serum C3 complement. A low serum C3implies a lesion other than MCNS, and a renal biopsy isindicated before trial of steroid therapy. Microscopic hematuria may be present in up to 25% of cases of MCNS butdoes not predict response to steroids. Additional laboratorytests, including electrolytes, blood urea nitrogen, creatinine,total protein, and serum albumin level, are performed basedon history and physical examination features. Renal ultrasound is often useful. Biopsy is performed when MCNS isnot suspected.
Transient proteinuria can be seen after vigorous exercise, fever, dehydration, seizures, and adrenergic agonist therapy. Proteinuria usually is mild (UPr/Cr<1), glomerular in origin, and always resolves within a few days. It does not indicate renal disease.
Postural (orthostatic) proteinuria is a benign condition defined by normal protein excretion while recumbent but significant proteinuria when upright. It is glomerular in nature, more common in adolescents and tall, thin individuals, and not associated with progressive renal disease. Many children with orthostatic proteinuria continue this process into adulthood.
Tubular proteinuria is characterized by preponderance of low-molecular-weight proteins in the urine and is suspected with acute tubular necrosis, pyelonephritis, structural renal disorders, polycystic kidney disease, and tubular toxins such as antibiotics or chemotherapeutic agents. The combination of tubular proteinuria with evidence of tubular electrolyte wasting and glycosuria is termed Fanconi syndrome.
Glomerular proteinuria is characterized by a combination of largeand small-molecular-weight proteins in the urine, variable levels of proteinuria, and often evidence of glomerular disease (hematuria, red blood cell casts, HTN, and renal insufficiency). Causes of glomerular proteinuria include glomerular capillary disruption (hemolytic uremic syndrome, crescentic glomerulonephritis); glomerular capillary immune complex deposition (poststreptococcal glomerulonephritis and lupus nephritis); and altered glomerular capillary permeability (MCNS, congenital NS).