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Canadian Journal of Gastroenterology
Volume 22 (2008), Issue 1, Pages 49-53
Original Article

Increase of Urinary 5-Hydroxyindoleacetic Acid Excretion but Not Serum Chromogranin a Following Over-The-Counter 5-Hydroxytryptophan Intake

Tisha Joy,1 Grace Walsh,1 Sonya Tokmakejian,2 and Stan HM Van Uum1,3,4

1Division of Endocrinology and Metabolism, Schulich School of Medicine and Dentistry, Canada
2Department of Biochemistry, Schulich School of Medicine and Dentistry, Canada
3Division of Clinical Pharmacology, Department of Medicine, Schulich School of Medicine and Dentistry, Canada
4Lawson Health Research Institute, University of Western Ontario, London, Ontario, Canada

Received 12 March 2007; Accepted 31 May 2007

Copyright © 2008 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


BACKGROUND: 5-hydroxyindoleacetic acid (5-HIAA) excretion is commonly measured for biochemical detection of carcinoid tumours. A 77-year-old woman was referred for elevated 24 h urine 5-HIAA excretion (510 μmol/day; normal is less than 45 μmol/day) and serum chromogranin A (CgA) (72.1 U/L; normal is less than 18 U/L), both subsequently normalized after discontinuation of 5-hydroxytryptophan (5-HTP). 5-HTP, a precursor of serotonin, is not commonly listed as a substance that increases 5-HIAA levels in urine. The effect of 5-HTP on CgA has not been previously described.

OBJECTIVES: To determine whether, and to what extent, oral 5-HTP increases urine 5-HIAA excretion and serum CgA levels in healthy volunteers.

PATIENTS AND METHODS: A randomized, prospective, double-blind, placebo-controlled crossover study, with a four-day washout period, was performed in a general community setting. Eight healthy subjects aged 22 to 58 years were recruited by advertising. Bedtime ingestion of 5-HTP 100 mg/day was compared with placebo ingestion for 10 days. Twenty-four hour urine excretion of 5-HIAA and serum CgA were the main outcome measures.

RESULTS: Median (range) urinary 5-HIAA excretion was 204 μmol/day (22 μmol/day to 459 μmol/day) during 5-HTP intake, compared with 18 μmol/day (12 μmol/day to 36 μmol/day) during placebo intake (P=0.017). 5-HTP did not affect clinical symptoms or serum CgA levels.

CONCLUSIONS: Oral 5-HTP increases urinary 5-HIAA excretion with considerable interindividual variation. In a small number of subjects, oral 5-HTP did not affect serum CgA levels. Therefore, increased 5-HIAA levels with normal CgA levels may suggest 5-HTP ingestion. The use of over-the-counter 5-HTP should be excluded as the cause of increased urinary 5-HIAA levels before initiating diagnostic tests to search for a carcinoid tumour. 5-HTP should be added to popular references as a substance that may cause increased 5-HIAA excretion.