title: A new classification plot for the C-peptide suppression test.
abstract: OBJECTIVE
  To evaluate the C-peptide suppression test as a screening test in patients with symptoms of hypoglycemia as compared to the standard fasting test.
  
  
  METHODS
  Retrospective discriminant analysis of data from C-peptide suppression tests.
  
  
  METHODS
  Clinical study.
  
  
  METHODS
  Patients with insulinomas and patients without insulinomas but having symptoms compatible with hypoglycemia.
  
  
  METHODS
  The results from C-peptide suppression tests of 26 patients with insulinomas and 100 patients without insulinomas were compared.
  
  
  METHODS
  A classification plot which introduces two discriminant parameters for the C-peptide suppression test: the ratio of [blood glucose]/[C-peptide] at the lowest C-peptide concentration and mean glycemia during insulin infusion.
  
  
  RESULTS
  In patients with insulinomas, minimal serum C-peptide levels were higher (1.81+/- 0.87 ng/mL; median 1.83 ng/mL; maximal suppression 37 +/- 24% of basal C-peptide levels) as compared to patients without insulinoma (0.40 +/- 0.15 ng/mL; median 0.30 ng/mL; maximal suppression of 75 +/- 9%; P<0.001). Mean glycemia during the test was lower in patients with insulinomas (30.8 +/- 3.3 vs. 47.5 +/- 8.3 mg/dL; P<0.001) as was the [blood glucose]/[C-peptide] ratio (21.9 +/- 14.6 vs. 139.2 +/- 43.8; P<0.001). Discriminant analysis revealed a specificity of 96% to rule out the diagnosis of 'insulinoma' at a 1% probability threshold with a sensitivity of 100%.
  
  
  CONCLUSIONS
  We developed a new classification plot for the C-peptide suppression test in order to accurately identify those patients whose symptoms of hypoglycemia are not due to endogenous hyperinsulinemia/insulinomas. Thus, the need for fasting tests and hospitalization costs can be reduced.
authors.affiliation: Department of Metabolic Diseases and Nutrition, Heinrich-Heine-University of Duesseldorf, Duesseldorf, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Saddig
authors.forename: Ralf
authors.initials: R
authors.lastname: Bender
authors.forename: Achim A R
authors.initials: AA
authors.lastname: Starke
mesh_terms: D007516:Adenoma, Islet Cell / Q000097:blood / Q000175:diagnosis*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002096:C-Peptide / Q000097:blood / Q000145:classification*; D005260:Female; D006801:Humans; D007003:Hypoglycemia / Q000097:blood / Q000175:diagnosis*; D007328:Insulin / Q000378:metabolism; D007329:Insulin Antagonists / Q000097:blood / Q000145:classification*; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000097:blood / Q000175:diagnosis*
chemical_list: D002096:C-Peptide; D007328:Insulin; D007329:Insulin Antagonists