Assessment of hyperinsulinaemia at the termination of the prolonged fast.
BACKGROUND
Traditional criteria to diagnose hyperinsulinaemic hypoglycaemia are based on insulin measurements by unspecific insulin assays. This study was performed to test whether these traditional criteria can be applied when insulin is measured by specific immunoassays.


METHODS
29 consecutive patients undergoing a prolonged fast were included; 11 patients with insulinoma and 18 healthy individuals. We determined plasma glucose, insulin, C-peptide, proinsulin, and beta-hydroxybutyrate concentrations at the termination of the fast. Insulin was measured by an unspecific radioimmunoassay (RIA) and a specific enzyme-linked immunosorbent assay (ELISA).


RESULTS
In 11 insulinoma patients, insulin concentrations at median plasma glucose concentration of 2.1 (range 1.3-2.5) mmol/l were 170 (76-340) pmol/l measured by RIA and 61 (11-156) pmol/l by ELISA. Insulin concentrations measured by RIA confirmed hyperinsulinaemia (i.e., >36 pmol/l, the proposed cut-off value for traditional insulin assays) in all insulinoma patients, whereas insulin concentrations measured by ELISA were <36 pmol/l in four patients. In three insulinoma patients, insulin concentrations measured by ELISA were <18 pmol/l, a proposed cut-off level to diagnose hyperinsulinaemia for specific insulin assays.


CONCLUSIONS
When insulin concentrations are measured by specific immunoassays in patients evaluated for fasting hypoglycaemia, traditional reference values cannot be applied.
Wiesli
Peter
P
Department of Internal Medicine, Division of Endocrinology and Diabetes, University Hospital of Zurich, CH-8091, Zurich, Switzerland. peter.wiesli@DIM.usz.ch
Brändle
Michael
M
Zapf
Jürgen
J
Seiler
Heidi
H
Zwimpfer
Cornelia
C
Spinas
Giatgen A
GA
Schmid
Christoph
C
D020155:3-Hydroxybutyric Acid / Q000097:blood; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000032:analysis; D002096:C-Peptide / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay; D005215:Fasting / Q000378:metabolism*; D005260:Female; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood* / Q000209:etiology; D007328:Insulin / Q000097:blood; D007340:Insulinoma / Q000150:complications; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000150:complications; D011384:Proinsulin / Q000097:blood; D011863:Radioimmunoassay; D012016:Reference Values; D012680:Sensitivity and Specificity; D013997:Time Factors
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D011384:Proinsulin; D020155:3-Hydroxybutyric Acid