Insulin Feedback After a Missed Dose
A 16-year-old with type 1 diabetes uses a long-acting basal insulin each evening and rapid-acting insulin with meals. During a school trip she skips her evening basal dose entirely and eats a large pasta dinner without rapid-acting insulin. Six hours later she is nauseated, thirsty, and breathing deeply. A classmate's glucometer reads 24 mmol/L (normal fasting 4–7 mmol/L). Her breath smells fruity. The teacher wants to give her a sugary snack because she 'looks unwell,' and a friend suggests waiting until morning to see if she improves. The group is 90 minutes from the nearest hospital.
1. Explain, using the roles of insulin and glucagon, why her blood glucose rose so high and why her breath smells fruity.
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Without basal or meal insulin, insulin-dependent tissues (muscle, adipose) cannot take up glucose, so blood glucose climbs well above the normal 4–7 mmol/L range. Low effective insulin removes the normal brake on glucagon, so the liver breaks down glycogen and performs gluconeogenesis, adding more glucose to the blood. Because cells cannot use glucose, they switch to fat oxidation, producing excess acetyl-CoA that the liver converts to ketone bodies. Acetone is volatile and gives the fruity breath; ketones are also acids, explaining the deep breathing as respiratory compensation. The key judgement is that this is a low-insulin state, not a 'sugar low,' so the fruity breath and very high reading point to ketone accumulation rather than hypoglycemia.
2. Evaluate the teacher's suggestion of a sugary snack and the friend's suggestion to wait until morning. What is the safest action?
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A sugary snack is dangerous: glucose is already extremely high, so adding carbohydrate without insulin worsens hyperglycemia and ketone production. Waiting until morning risks progression to diabetic ketoacidosis, which can cause vomiting, dehydration, electrolyte imbalance, and loss of consciousness. The safest action is urgent medical care now-calling emergency services or traveling to the hospital-while monitoring her breathing and consciousness. If rapid-acting insulin is available and dosing is known, it may be given under medical guidance, but it should never be improvised without knowing the dose. The reasoning rests on recognizing a hyperglycemic emergency, not on treating 'looking unwell' as hypoglycemia.