Insulin levels measured with an insulin-specific assay in patients with fasting hypoglycaemia related to endogenous hyperinsulinism.
OBJECTIVE
The finding of insulin levels above a minimum threshold at the time of symptomatic hypoglycaemia is crucial in the diagnosis of endogenous hyperinsulinism. The aim of this study was to evaluate insulin levels at the time of hypoglycaemia with an insulin-specific assay in such patients.


METHODS
We measured insulin levels in 15 patients with fasting hypoglycaemia related to endogenous hyperinsulinism using an insulin-specific immunoradiometric assay (IRMA) without any significant cross-reaction with intact proinsulin.


RESULTS
Insulin levels were below 6 mIU/l in all the samples taken at the time of symptomatic hypoglycaemia in 6/15 patients, and in some of the samples in three patients; insulin levels were below 3 mIU/l in samples from 5 patients. C-peptide levels were above 0.6 ng/ml in all these samples. The lowest proinsulin level was 35 pmol/l. Insulin levels were measured with a less specific RIA (40% cross-reaction with proinsulin) in 8/15 patients and were above 6 mIU/l in all samples in seven patients, and all but one sample in the 8th patient. Mean concomitant C-peptide and insulinoma size were lower in those patients with insulin-IRMA levels below 6 mIU/l.


CONCLUSIONS
Symptomatic hypoglycaemia below 0.45 g/l can result from insulin levels below 6 or even 3 mIU/l; lower insulin levels and secretion could be observed preferentially in small insulinomas. If an insulin assay devoid of any significant cross-reaction with intact proinsulin is employed, measuring C-peptide (and/or proinsulin) levels at the time of symptomatic hypoglycaemia is mandatory to make the diagnosis of endogenous hyperinsulinism.
Department of Endocrinology, Hopital Rangueil, CHU Toulouse, 1 Avenue Jean-Poulhes, TSA 50032, 31059 Toulouse-Cedex 9, France.
Delphine
D
Vezzosi
Antoine
A
Bennet
Josette
J
Fauvel
Catherine
C
Boulanger
Othman
O
Tazi
Jean-Pierre
JP
Louvet
Philippe
P
Caron
D000328:Adult; D000368:Aged; D001786:Blood Glucose; D002096:C-Peptide / Q000097:blood; D005215:Fasting; D005260:Female; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood / Q000175:diagnosis*; D007003:Hypoglycemia / Q000097:blood / Q000175:diagnosis*; D015592:Immunoradiometric Assay / Q000379:methods*; D007328:Insulin / Q000097:blood*; D007340:Insulinoma / Q000097:blood / Q000175:diagnosis; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000097:blood / Q000175:diagnosis; D011384:Proinsulin / Q000097:blood
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D011384:Proinsulin