Objective determination of the optimal red blood cell count in diagnostic peritoneal lavage done for abdominal stab wounds

The purpose of this study was to determine objectively the optimal value or positivity criterion for red blood cell counts in diagnostic peritoneal lavage in stab wounds to the anterior abdomen. Our study group consisted of 91 consecutive adults with abdominal stab wounds who underwent peritoneal lavage. We excluded those patients who met criteria for immediate laparotomy and those with negative stab wound exploration. We divided the patients into two groups based on outcome. Group 1 consisted of those who had undergone laparotomy and had findings that required surgical intervention. Group 2 patients had either undergone laparotomy but had no injury requiring surgical intervention or had no surgery and a benign hospital course and follow-up. Receiver operator characteristic analysis was done on the diagnostic peritoneal lavage RBC counts for both groups. The overlap between the groups was minimal, with 75% of patients in Group 1 having > 120,000 RBC/mm3 and 75% of patients in Group 2 having < 486 RBC/mm3 in the lavage effluent. Using the observed probability of 23.1% of patients with abdominal stab wounds requiring surgery, a RBC count of 50,000/mm3 discriminated best those patients who required surgery from those who did not.