Spot urine 5-hydroxy indole acetic acid and acute appendicitis

Appendectomy for suspected appendicitis cases is a common procedure. Its clinical diagnosis needs to be supported by accurate confirmatory tests. No single paraclinical test with a high degree of sensitivity and specificity is available for its diagnosis. The appendix contains numerous serotonin-producing cells (enterochromaffin cells). In the inflammatory process and subsequent cell injury, serotonin is released and converted to 5-HIAA (5-hydroxy indole acetic acid). We studied the elevation of 5-HIAA in the spot urine of acute appendicitis patients.

5-HIAA was measured by high-performance liquid chromatography in the spot urine samples of 40 healthy individuals and 166 patients who presented to emergency units of the university hospitals with acute abdominal pain. The results of the urine concentrations were compared to the histopathology reports of the removed appendices and the final diagnosis of other diseases.

From 80 cases with a presumptive diagnosis of appendicitis, 73 were operated on and seven cases discharged after a few hours observation. Sixty-five out of 66 documented appendicitis patients showed a striking increase of urinary spot 5-HIAA with significant differences vs. all cases of healthy control individuals (P < 0.001). The 5-HIAA values of all of the negative appendectomy cases (n = 7) and all of the discharged cases after the observation period (n = 7) were within healthy control ranges. The mean value of the appendicitis group (42.76 +/- 2.26 mumol/L) was also significantly higher vs. all other acute abdomens which could mimic acute appendicitis (P < 0.05) excepting gastroenteritis patients. Considering 20 mumol/L as the cutoff value sensitivity, specificity, positive and negative predictive values of this test for discriminating appendicitis in clinically suspected patients were 98%, 100%, 100% and 93%, respectively and in all acute abdomens were 98%, 71%, 69% and 98.6%, respectively. The patients with gastroenteritis also showed elevation of 5-HIAA (43.05 +/- 2.7 mumol/L) vs. other nonappendicitis groups (P < 0.05).

We have concluded that measurement of 5-HIAA in spot urine is a highly reliable test supporting the clinical diagnosis of appendicitis and if it does not show an increase, appendicitis can be ruled out with a very high degree of confidence which helps to reduce unnecessary appendectomies. In clinically suspected appendicitis patients with diarrhea, an increase of 5-HIAA may not confirm the diagnosis.