IDENTIFICATION OF CAUSE OF HYPOGLYCEMIA
PLASMA INSULIN AND C-PEPTIDE
Increase in
Insulin and C-peptide in the presence of hypoglycemia indicates islet-cell
tumors, autoimmune insulin secretion, and drug-induced (sulphonylureas,
repaglinide) causing endogenous hyperinsulinaemia.
Decrease in insulin and C-peptide
indicates presence of other secondary conditions like chronic renal failure (as
C-peptide is excreted by kidney), liver disease, alcohol induced, anorexia
nervosa, etc.
Increase in insulin but decrease in
C-peptide indicates administration of exogenous insulin, Insulin anti-receptor
antibodies (IR-A).
PLASMA Β-HYDROXYBUTYRATE
Hypoglycemia
due to hyerinsulinemia shows low ketone bodies. In hypoglycemia due to other
conditions like liver disease, anorexia nervosa, hypopituitarism etc, this ketone
body is raised.
PLASMA PROINSULIN
Normally
only <20% of insulin is released in circulation. In islet cell tumor,
circulating proinsulin is increased.
INSULIN ANTIBODIES
The presence
of insulin antibodies, due to pre-exposure to exogenous insulin may give false
high plasma insulin concentrations. Since C-peptide does not cross-react with
insulin antibodies, its measurement can be used as index of β-cell function.
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