Elevated Blood Urea Nitrogen: An Aid to the Diagnosis of Intraperitoneal Rupture of the Bladder

Abstract

A retrospective analysis was done on 18 patients with bladder rupture. At the time of hospitalization 9 patients with extraperitoneal rupture had an average blood urea nitrogen of 14.2 ± 2.2mg. per cent, which did not vary from the normal laboratory value of 14.5 ± 7.4mg. per cent, and 9 patients with intraperitoneal rupture had an average blood urea nitrogen of 29.9 ± 7.6mg. per cent, which was significantly different (p <0.0001) from the discharge blood urea nitrogen (12.9 ± 2.2mg. per cent) and the normal laboratory value. The 2 groups of patients were comparable since no significant difference was found in age, sex, mode of injury, hematocrit value or associated injuries. To quantify the significance of our observation an experimental study was done on dogs with 1) surgically created intraperitoneal bladder ruptures, 2) intraperitoneal injections of urine, 3) intraperitoneal injections of blood and 4) a control group. A sequential increase in serum blood urea nitrogen was found in dogs with intraperitoneal bladder rupture 1 hour after injury to an empty bladder. An intraperitoneal injection of urine showed that a high blood urea nitrogen could be found as early as a half hour after the injection and that it would be cleared totally between 3 and 6 hours. Serum creatinine levels were not as good indicators of intraperitoneal urine, becoming significantly different from control values later than the blood urea nitrogen. All creatinine levels were within the normal human laboratory value, suggesting a poor and sluggish index of this type of injury.Our study shows that increased blood urea nitrogen is a presenting laboratory finding and a sensitive index in the detection of patients who have sustained intraperitoneal rupture of the bladder. Awareness of this finding may lead to an early diagnosis in otherwise clinically unsuspected cases. This test will not provide for a diagnosis of extraperitoneal bladder ruptures.