Urinary 5-hydroxy indole acetic acid as a test for early diagnosis of acute appendicitis

Acute appendicitis (AA) is the most common abdominal emergency. The appendix has abundant serotonin containing cells. Upon inflammation, serotonin is released in the blood and converted into 5-HIAA (5-hydroxy indole acetic acid). Measurement of the urine 5-HIAA (U-5-HIAA) could be a reliable marker of inflammation of the appendix. We have compared the powers of test performance of spot U-5-HIAA and spot U-5-HIAA/creatinin with other routine laboratory tests used for the diagnosis of acute appendicitis.

Urine, serum, and blood samples of 110 patients who were admitted and observed in the emergency units of two university hospitals were studied. 5-HIAA was measured using HPLC, C-reactive protein by immunoturbidometry, WBC by electronic cell counting, and urine creatinine by the Jaffe method. Diagnostic accuracy of the various tests was evaluated by receiver operating characteristic (ROC) analysis.

The mean of spot U-5-HIAA in 39 patients with AA (nongangrenous) was 32 +/- 2.6 micromol/L, which was much higher than the mean of 40 non-appendicitis patients (NA) (5.5 +/- 0.6), 10 follicular hyperplasia (7.5 +/- 2.1), and 50 healthy control cases (4.1 +/- 0.5) with P < 0.001. The concentration of U-5-HIAA in 21 patients with gangrenous appendicitis (GA) (13.8 +/- 2.1) was also higher than NA patients and healthy individuals but lower than AA cases (P < 0.05). Considering 10 micromol/L as the cutoff point, this test shows 84% sensitivity and 88% specificity, with 90% and 81% positive and negative predictive values, respectively. The area under ROC curve (AUC) of U-5-HIAA in the diagnosis of AA (AUC = 0.903) was much larger than AUCs of U-5-HIAA/Cr (0.787), WBC (0.703), and CRP (0.660).

: Urinary secretion of 5-HIAA increases significantly in acute appendicitis and measurement of spot U-5-HIAA gives higher diagnostic accuracy than other routine laboratory tests. While the inflammation progresses to necrosis of the appendix, the concentration of 5-HIAA decreases. This decrease could be a warning sign of perforation of the appendix.