Post-Bariatric Hypoglycaemia

Post-bariatric hypoglycaemia is late postprandial hypoglycaemia, usually 1 to 3 hours after a meal, after Roux-en-Y gastric bypass and less often after sleeve gastrectomy. It typically appears more than 1 year after surgery.

Severe neuroglycopenic disease affects roughly 1% of patients, although reports vary widely. Mild asymptomatic glucose falls under 3.0 mmol/L on continuous monitoring are much more common.

It differs from early dumping, which occurs within 1 hour of eating and causes gastrointestinal and vasomotor symptoms with normal glucose.

Pathophysiology.

Rapid delivery of nutrient to the small bowel produces an exaggerated glucagon like peptide-1 and insulin response, with higher insulin sensitivity and impaired glucagon counter regulation.

Bile acid changes and altered gut hormones contribute. Beta cell hypertrophy is inconsistent and does not explain the syndrome.

• Adrenergic and neuroglycopenic symptoms 1 to 3 hours after a carbohydrate rich meal: sweating, palpitations, confusion, visual change, seizure.
• Symptoms may occur after exercise. Fasting hypoglycaemia is not typical.

Red flags.

• Seizure, loss of consciousness or injury.
• Hypoglycaemia while driving or in hazardous work.
• Fasting episodes (look for another cause).

• Documented low glucose with symptoms that resolve when glucose is restored.
• Mixed meal test with glucose and insulin at baseline and every 30 minutes for 3 hours: glucose under 3.0 mmol/L (54 mg/dL) with symptoms and inappropriately detectable insulin supports the diagnosis. Continuous glucose monitoring shows the pattern.
• Do not use an oral glucose tolerance test, because low glucose is common in asymptomatic people after bypass.
• Exclude other causes: sulphonylurea screen, insulin autoantibodies, a 72-hour fast if any fasting episodes occur, morning cortisol, and imaging only if fasting hypoglycaemia points to insulinoma.

Differential diagnosis.

• Early dumping syndrome.
• Insulinoma.
• Insulin autoimmune syndrome and factitious insulin or sulphonylurea use.
• Adrenal insufficiency and alcohol related hypoglycaemia.
• Non-surgical reactive hypoglycaemia.

• Diet: 6 small meals daily with about 30 g of slowly absorbed carbohydrate or less each, combined with protein and fat. Avoid refined sugars and drinking with meals.
• Acute hypoglycaemia: 15 g oral glucose (not more, to limit a rebound), repeat at 15 minutes. Glucagon 1 mg intramuscularly if unable to take oral intake.
• Acarbose 50 to 100 mg with each main meal.
• Diazoxide 3 to 8 mg/kg daily in two or three divided doses, starting low (about 25 mg twice daily). Watch for oedema, hypertrichosis and hyperglycaemia.
• Octreotide 50 micrograms subcutaneously 30 minutes before meals, or a long acting preparation, with attention to gallstones, steatorrhoea and glucose rise.
• Continuous glucose monitoring with low glucose alarms. Advise against driving until control is secure.
• Refractory disease: gastric tube feeding into the remnant stomach, or reversal or revision of the bypass. Partial pancreatectomy is not advised because relapse is common.

Special groups. Pregnancy after bypass: avoid the oral glucose tolerance test and use fasting glucose, HbA1c or continuous monitoring to assess glucose.

Monitoring. Symptom diary and continuous glucose data every visit, weight and nutrition (vitamin B12, iron, calcium, vitamin D).

Referral and escalation. Endocrinology and bariatric team for confirmed disease, and urgently for seizures or driving risk.