title: Increase of urinary 5-hydroxyindoleacetic acid excretion but not serum chromogranin A following over-the-counter 5-hydroxytryptophan intake.
abstract: 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 micromol/day; normal is less than 45 micromol/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.
  
  
  OBJECTIVE
  To determine whether, and to what extent, oral 5-HTP increases urine 5-HIAA excretion and serum CgA levels in healthy volunteers.
  
  
  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 micromol/day (22 micromol/day to 459 micromol/day) during 5-HTP intake, compared with 18 micromol/day (12 micromol/day to 36 micromol/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.
authors.affiliation: Division of Endocrinology and Metabolism, University of Western Ontario, London, Canada.
authors.forename: Tisha
authors.initials: T
authors.lastname: Joy
authors.forename: Grace
authors.initials: G
authors.lastname: Walsh
authors.forename: Sonya
authors.initials: S
authors.lastname: Tokmakejian
authors.forename: Stan Hm
authors.initials: SH
authors.lastname: Van Uum
mesh_terms: D006916:5-Hydroxytryptophan / Q000008:administration & dosage / Q000378:metabolism*; D000328:Adult; D015415:Biomarkers / Q000378:metabolism*; D002276:Carcinoid Tumor / Q000175:diagnosis; D053379:Chromogranin A / Q000097:blood*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D006897:Hydroxyindoleacetic Acid / Q000652:urine*; D008297:Male; D008875:Middle Aged; D004366:Nonprescription Drugs / Q000008:administration & dosage / Q000378:metabolism; D011446:Prospective Studies
chemical_list: D015415:Biomarkers; D053379:Chromogranin A; D004366:Nonprescription Drugs; D006897:Hydroxyindoleacetic Acid; D006916:5-Hydroxytryptophan