Endocrine Abstracts

Introduction: Some functional neuroendocrine tumours (NETs) secrete serotonin, leading to the symptoms of carcinoid syndrome (e.g. diarrhoea and flushing). In this condition, increased urinary concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) are often detected. Measurement of 24-hour urinary 5-HIAA is therefore used to investigate patients with confirmed or suspected carcinoid syndrome. We sought to evaluate the appropriateness and effectiveness of this test in a UK general hospital that also hosts an ENETS Centre of Excellence.

Methods: Retrospective audit of all patients undergoing 24-h urinary 5-HIAA testing at Royal Liverpool University Hospital during 2017.

Results: 284 urinary 5-HIAA tests were performed on 264 patients by clinicians from 19 specialties, most of whom were not directly involved in managing NET patients. 49(17%) tests were performed in patients with known NETs, 133(47%) tests were performed to investigate symptoms possibly suggestive of carcinoid syndrome, 62(22%) tests were performed to investigate hypertension and 40(14%) tests were performed for various other indications. Most patients (other than those with known NETs) did not undergo any additional biochemical tests such as measurement of plasma chromogranin A. 27 patients (18 of whom who had known NETs) had urinary 5-HIAA concentrations above the upper limit of normal. 7/133 tests in patients with suspected NETs, 3/62 tests in patients with hypertension and 1/40 test from the ‘other’ category were elevated, but only one of these patients was subsequently found to have a small bowel NET. Four patients with elevated results had repeat tests, two of which were normal. Six patients who were not already known to have a NET therefore had isolated elevated urinary 5-HIAA tests but did not have appropriate additional investigations to confirm or rule out a NET.

Conclusions: Use of 24-h urinary 5-HIAA testing resulted in only one new NET diagnosis in 2017. 24-h urinary 5-HIAA testing was often inappropriately performed, especially in patients with suspected secondary hypertension. Most patients who had elevated urinary 5-HIAA results did not have appropriate repeat or additional investigations. Further education about this test is warranted for clinicians who are not directly involved in managing NET patients.