Which test result would most specifically support uroabdomen as the cause of colic?

• A. Peritoneal fluid creatinine markedly higher than serum creatinine
• B. Low WBC count
• C. Elevated glucose in peritoneal fluid
• D. Normal peritoneal fluid creatinine

Answer: (A)

When urine leaks into the abdominal cavity, substances that are high in urine show up in the peritoneal fluid. Creatinine is one of those substances, so the peritoneal fluid creatinine becomes markedly higher than the serum creatinine. That pronounced difference is the most specific clue that uroabdomen is the cause of colic, because urine consistently has higher creatinine than blood and the fluid in the abdomen reflects that. The other options don’t point to urine leakage: a low white blood cell count isn’t diagnostic of uroabdomen, elevated glucose in the peritoneal fluid isn’t a typical marker of urine leakage, and normal peritoneal creatinine would argue against uroabdomen.