Analysis of peritoneal fluid in urinary ascites.

Urinary ascites may be the most common cause of ascites in the neonate, and should be suspected in an infant with abdominal distention, oliguria, hyponatremia, and hyperkalemia. The diagnosis is confirmed when analysis of the peritoneal fluid shows creatinine, urea, and potassium concentrations higher than corresponding serum concentrations. The establishment of adequate urinary drainage by catheterization of the bladder or nephrostomy rapidly corrects electrolyte abnormalities.