Hypoglycemia

Today we discussed hypoglycemia. Outside context of medications, this is very rare, but must be investigated. Some important points that came up:


A framework for causes (loosely based on Harrison's):

1) Alimentary / postprandial

"Pseudo": normal glucose with symptoms. Possible role for 5h glucose tolerance test
"True": Occurs with rapid gastric emptying (gastrectomy, pyeloroplasty, refeeding, post-vagotomy)

2) Fasting

Decreased supply (i.e. not an insulin problem):

Hormone deficiency (pituitary or adrenal)
Liver failure (late)Starvation (late)
Enzyme deficiency (in childhood/neonate)
EtOH (from decreased NADH)
Medications (sulfa, salicylates, pentamidine, quinolones)

Increased demand (i.e. an insulin problem)

Low insulin- IgF-secreting tumor (sarcoma, RCC, HCC)

High insulin
Exogenous insulin
Insulin secretagogue (e.g. sulfonylurea)
Insulinoma
Insulin receptor antibodies (autoimmune)


Pts usually become symptomatic (neuroglycopenic or autonomic symptoms) at BG less than 2.5-3

Need to confirm hypoglycemia (with serum, not capillary glucose), that symptoms are caused by it, and that glucose reverses the symptoms (sometimes referred to as Whipple's triad)

Best test to rule in insulinoma or other neuroendocrine tumor after ruling out medications and adrenal insufficiency is 72h fast

Pts are admitted to hospital, and fasted for up to 72h, allowed to take calorie-free fluids only, and are active during waking hours. Blood for measurement of glucose (serum, not accucheck), insulin, c-peptide are taken q6h, with measurement of insulin and c-peptide when BG less than 3.3mM

Endpoints of the test are any of: 1) BG below 2.5, 2) neuroglycopenic symptoms, 3) 72h elapsed
-Also give 1mg glucagon and measure BG q 20min x 3
-Feed the pt
-Insulin level over 3uU/mL when BG is below 3.0 is highly suggestive of insulinoma.
-C-peptide is measured to differentiate endogenous vs. exogenous insulin (with exogenous insulin, insulin level is high, but c-peptide is undetectable since exogenous insulin does not have c-peptide)

If test is positive, imaging studies: CT/MRI/US

Therapy for insulinoma is surgery; medical management is octreotide or diazoxide.

NB- look for MEN1 if insulinoma (pancreatic endocrine tumors, pituitary tumors, primary hyperparathyroidism)

Link:

Click here for 2009 practice guideline for this problem from the Journal of Clinical Endocrinology and Metabolism