Which measure best distinguishes uroabdomen from other causes of peritoneal effusion?

• A. Peritoneal to serum creatinine ratio
• B. Total protein in peritoneal fluid
• C. Neutrophil count in peritoneal fluid
• D. Blood type matching

Answer: (A)

The key idea is using how much creatinine is in the abdominal fluid compared with the blood. If urine leaks into the peritoneal cavity (uroabdomen), the fluid there contains creatinine at levels similar to urine, which are much higher than the creatinine in blood. Measuring the peritoneal creatinine and comparing it to serum creatinine gives a high ratio—typically above about 2—that strongly indicates uroabdomen. This approach is more specific for urine leakage than other fluid tests, because other causes of peritoneal effusion don’t raise peritoneal creatinine to urine-like levels. Total protein, neutrophil count, or even blood-type checks can be affected by many different conditions and aren’t as diagnostic for distinguishing uroabdomen.