title: Evaluation of endocrine tests. D: the prolonged fasting test for insulinoma.
abstract: OBJECTIVE
  To establish the diagnostic performance of the prolonged fasting test in patients suspected of insulinoma.
  
  
  METHODS
  We included all patients who were referred to our department between August 1995 and August 2006 with a clinical suspicion of insulinoma. Insulinoma was diagnosed by a positive Whipple's triad during the prolonged fast in combination with an insulin/C-peptide ratio below 1. The presence of insulinoma was confirmed by histopathological data, which was considered the golden standard. If the prolonged fast was negative, long-term follow-up was obtained.
  
  
  RESULTS
  Ten patients had a positive Whipple's triad during the prolonged fast: eight had a histologically proven insulinoma, and two had factitious hypoglycaemia (insulin/C-peptide ratio >1.0) One additional patient likely had an insulinoma, but the Whipple's triad remained absent at up to 56 hours of fasting. Follow-up (median 53 months (3 to 142) in 76% of patients with a negative fasting test revealed no missed cases of insulinoma. During the prolonged fast the glucose, insulin and C-peptide concentrations overlapped in patients with and without insulinoma.
  
  
  CONCLUSIONS
  In our centre, the prolonged fasting test defined as a positive Whipple's triad in combination with an insulin/C-peptide ratio <1 had a sensitivity of 88.9% and a specificity of 100% for the diagnosis of insulinoma.
authors.affiliation: Department of Endocrinology and Metabolism, Academic Medical Centre, University of Amsterdam, the Netherlands. a.c.vanbon@amc.nl
authors.forename: A C
authors.initials: AC
authors.lastname: van Bon
authors.forename: N
authors.initials: N
authors.lastname: Benhadi
authors.forename: E
authors.initials: E
authors.lastname: Endert
authors.forename: E
authors.initials: E
authors.lastname: Fliers
authors.forename: W M
authors.initials: WM
authors.lastname: Wiersinga
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000032:analysis*; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood; D005215:Fasting / Q000502:physiology; D005260:Female; D006801:Humans; D007003:Hypoglycemia / Q000097:blood; D007328:Insulin / Q000097:blood; D007340:Insulinoma / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D010190:Pancreatic Neoplasms / Q000175:diagnosis*; D011237:Predictive Value of Tests; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin