Spot urinary 5-hydroxyindoleacetic acid is not an ideal diagnostic test for acute appendicitis

There is growing evidence to suggest the use of urinary 5-hydroxyindoleacetic acid (5-HIAA) test to help with the diagnosis of appendicitis. The aim of our study was to establish whether urinary 5-HIAA could be used as an effective diagnostic test for acute appendicitis.

A prospective double-blinded study was carried out from December 2014 to October 2015. Patients admitted to the emergency surgical ward of a teaching hospital with suspected appendicitis were included in the study. The diagnostic accuracy of the test was measured by receiver operating characteristic curve.

Ninety-seven patients were divided into 2 groups: acute appendicitis (n=38) and other diagnosis (n=59). The median value of urinary 5-HIAA was 24.19μmol/L (range, 5.39-138.27) for acute appendicitis vs 18.87μmol/L (range, 2.27-120.59) for other diagnosis group (P=.038). The sensitivity and specificity of urinary 5-HIAA at a cutoff value of 19μmol/L were 71% and 50%, respectively. Receiver operating characteristic analysis showed that the area under curve was 0.64 (confidence interval [CI], 0.513-0.737) for urinary 5-HIAA, which was lower than white blood cell count (0.69; CI, 0.574-0.797), neutrophil count (0.68; CI, 0.565-0.792), and C-reactive protein (0.76; CI, 0.657-0.857). There was no significant difference in the median values of 5-HIAA between different grades of severity of appendicitis (P=.704).

Urinary 5-HIAA is not an ideal test for the diagnosis of acute appendicitis.