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Hypoglycemia: Diabetic & Nondiabetic Evaluation

Name: Hypoglycemia: Diabetic & Nondiabetic Evaluation
Creator: Veli Bakalov, MD

Treat the low fast, then let insulin and C-peptide name the cause

Endocrinology·Diabetes & Metabolism·5 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Evaluate nondiabetic hypoglycemia only after the Whipple triad: symptoms, glucose <55 mg/dL and relief when glucose is raised.
An alert patient takes 15–20 g of oral glucose and rechecks in 15 minutes; a patient who cannot swallow gets IV dextrose or IM/intranasal glucagon.
Glucagon fails when glycogen is depleted (starvation, alcohol); give dextrose with thiamine instead.
Sulfonylurea hypoglycemia is prolonged and recurrent: admit for dextrose infusion plus octreotide to block insulin release.
Hypoglycemia unawareness (long-standing type 1, tight control, autonomic neuropathy, β-blockers) is reversed by relaxed targets, 2–3 weeks of strict hypoglycemia avoidance and CGM.
Draw insulin, C-peptide, proinsulin, β-hydroxybutyrate and an oral hypoglycemic screen during a spontaneous low or a supervised 72-hour fast.
High insulin with low C-peptide means exogenous insulin; high insulin and C-peptide means insulinoma (localize with CT or endoscopic ultrasound) or secretagogue use (positive screen).
Low insulin with low ketones suggests an IGF-2–secreting tumor; low insulin with high ketones suggests adrenal insufficiency, organ failure, sepsis, starvation or alcohol.
Hypoglycemia 1–3 hours after meals following gastric bypass reflects GLP-1–driven hyperinsulinism and is treated first with dietary change.

Recognizing hypoglycemia

Whipple triad. In people without diabetes, hypoglycemia is diagnosed only when three things coincide: compatible symptoms, a plasma glucose below about 55 mg/dL measured at that moment, and relief when glucose is raised. Without the triad no workup is needed; postprandial symptoms with normal glucose are not hypoglycemia.

Levels in diabetes. Level 1 is glucose below 70 mg/dL, level 2 is below 54 mg/dL and clinically significant, and level 3 is any severe event with altered mental or physical status requiring another person's help. Insulin and insulin secretagogues cause nearly all hypoglycemia in diabetes, with missed meals, exercise, alcohol, CKD, older age and tight targets adding risk; level 2 or 3 events should prompt a review of the regimen.

Symptoms. Neurogenic symptoms come from sympathoadrenal discharge: adrenergic tremor, palpitations and anxiety, and cholinergic sweating and hunger. Neuroglycopenic symptoms reflect brain glucose deprivation: confusion, behavior change, slurred speech, focal deficits that mimic stroke, seizures and coma, so glucose is checked in anyone with altered mental status or a new deficit.

Treatment and prevention in diabetes

Alert and able to swallow15–20 g of glucose (tablets or gel preferred, or about 4 oz of juice); fatty foods such as chocolate slow absorption.
Recheck in 15 minutesRepeat until glucose is ≥70 mg/dL, then give a snack or meal.
Cannot swallow, no IV accessNothing by mouth (aspiration risk); glucagon 1 mg IM or SC, or 3 mg intranasal, which a bystander can give.
IV accessDextrose 25 g (D50) followed by a dextrose infusion; thiamine with glucose in malnourished or alcohol-using patients.

Glucagon. Glucagon raises glucose by mobilizing hepatic glycogen, so it fails when glycogen is depleted, as in starvation and alcohol-related hypoglycemia. It should be prescribed for everyone taking insulin or at high risk of severe hypoglycemia.

Sulfonylurea hypoglycemia. Long-acting agents such as glyburide, especially in older adults and CKD, cause prolonged and recurrent lows, so patients are admitted for a dextrose infusion and frequent glucose checks. Dextrose stimulates further sulfonylurea-driven insulin release and rebound lows; octreotide blocks that secretion and is the specific antidote.

Hypoglycemia unawareness. Recurrent hypoglycemia lowers the glucose threshold for epinephrine release and warning symptoms (hypoglycemia-associated autonomic failure), so neuroglycopenia arrives unannounced. Risk rises with long-standing type 1 diabetes, intensive control, autonomic neuropathy, β-blockers (which blunt tremor and palpitations but not cholinergic sweating), alcohol and older age. Management is to loosen targets, strictly avoid hypoglycemia for 2–3 weeks, which partly restores awareness, and use CGM with low-glucose alarms.

Evaluating hypoglycemia without diabetes

Ill or medicated patients. Look first for an obvious cause: drugs (insulin, secretagogues, alcohol, pentamidine, quinine), critical illness (hepatic, renal or cardiac failure, sepsis, starvation), cortisol deficiency, or a large non-islet cell tumor.

Seemingly well patients. Endogenous hyperinsulinism and surreptitious or malicious drug use must be excluded. Hormone levels are interpretable only during hypoglycemia, so a critical sample is drawn at a spontaneous episode, during a supervised 72-h fast for fasting symptoms (most insulinomas become hypoglycemic within 48 h), or after a mixed meal for postprandial symptoms. Measure glucose, insulin, C-peptide, proinsulin, β-hydroxybutyrate and a sulfonylurea/meglitinide screen, then give 1 mg IV glucagon: a rise of ≥25 mg/dL shows that insulin or IGF action had been preserving liver glycogen.

Critical-sample patterns

Cause	Insulin	C-peptide	Proinsulin	β-OHB	Other
Exogenous insulin	↑	↓	↓	↓	Drug screen negative
Insulinoma	↑	↑	↑	↓	Drug screen negative; localize
Sulfonylurea or meglitinide	↑	↑	↑	↓	Drug screen positive
IGF-2–secreting tumor	↓	↓	↓	↓	Low IGF-1, high IGF-2:IGF-1 ratio
Non-insulin-mediated	↓	↓	↓	↑	Little glucagon response

Glucagon raises glucose ≥25 mg/dL in the first four patterns.

Specific causes

Insulinoma. The most common functioning pancreatic neuroendocrine tumor causes fasting neuroglycopenia, often mistaken for seizures or psychiatric illness, and weight gain from frequent eating. About 90% are benign, solitary and under 2 cm; about 5–10% arise in MEN1, where they may be multiple, so calcium and PTH (and prolactin) are checked. After biochemical proof, the tumor is localized with multiphase CT or MRI and endoscopic ultrasound, with selective arterial calcium stimulation if imaging is negative. Enucleation or partial pancreatectomy is usually curative; diazoxide, which opens β-cell K-ATP channels, or octreotide controls symptoms when surgery is not possible.

Factitious hypoglycemia. Pharmaceutical insulin contains no C-peptide, so injected insulin gives high insulin with suppressed C-peptide and proinsulin. Healthcare workers and relatives of people with diabetes are classic, and malicious administration must be considered. Some insulin analogs are missed by immunoassays, so a suppressed C-peptide with hypoglycemia and low ketones points to exogenous insulin even when measured insulin looks unimpressive. Secretagogue ingestion mimics insulinoma and is identified only by the drug screen.

Non-islet cell tumor hypoglycemia. Large mesenchymal tumors (solitary fibrous tumor, sarcoma, mesothelioma) and hepatocellular carcinoma may secrete incompletely processed big IGF-2, which activates insulin receptors and suppresses insulin, C-peptide, ketones and IGF-1. Resection is curative; glucocorticoids help meanwhile.

Non-insulin-mediated causes. Adrenal insufficiency, hypopituitarism, liver failure, renal failure, sepsis, starvation (including anorexia nervosa) and alcohol cause hypoglycemia with low insulin and typically high ketones. Ethanol raises the NADH/NAD+ ratio and blocks gluconeogenesis, so a binge with little food can cause hypoglycemia hours later once glycogen is spent. Suspected adrenal insufficiency is confirmed with a cosyntropin stimulation test and treated with hydrocortisone.

Post-bariatric hypoglycemia. Months to years after Roux-en-Y gastric bypass, rapid carbohydrate delivery to the small bowel triggers exaggerated GLP-1 and insulin secretion, with hypoglycemia 1–3 h after meals, distinct from early dumping within 30 minutes. A mixed-meal test is used rather than an oral glucose tolerance test. Small, frequent, protein-rich meals low in simple carbohydrate come first, then acarbose, then octreotide or diazoxide. Noninsulinoma pancreatogenous hypoglycemia (nesidioblastosis) causes similar postprandial episodes from diffuse β-cell hyperfunction.