MKSAP quiz: Nocturnal hypoglycemia in type 1 diabetes

This month's quiz asks readers to evaluate a 21-year-old man with type 1 diabetes being seen in the office for a follow-up to a recent hospitalization.


A 21-year-old man comes to the office for a follow-up evaluation. He has a 12-year history of type 1 diabetes mellitus and a recent HbA1c value of 8.2%. Two days ago, he was brought to the emergency department after having a seizure at 3 a.m. in his dormitory. Earlier that day, he ate a hearty dinner, played basketball with friends for 3 hours, and then had three beers at a local microbrewery. His glucose monitor showed a blood glucose level of 163 mg/dL (9.0 mmol/L) before he went to bed at 11 p.m. His initial plasma glucose level in the emergency department was 28 mg/dL (1.6 mmol/L). He was given intravenous glucose and recovered fully. His only medications are insulin detemir before breakfast and dinner and insulin aspart before all meals.

Physical examination shows a fit, muscular young man. Vital signs are normal; BMI is 19. All other physical examination findings are normal.

Laboratory studies show an HbA1c value of 8.2%.

Which of the following is the most appropriate advice related to evening exercise to give this patient?

A. Avoid evening exercise
B. If alcohol is consumed, drink only light beer
C. Eat complex carbohydrates at bedtime
D. Omit the evening dose of insulin detemir and insulin aspart


MKSAP Answer and Critique

The correct answer is C. Eat complex carbohydrates at bedtime. This item is available to MKSAP 16 subscribers as item 79 in the Endocrinology section. Information about MKSAP 16 is available online.

This patient should eat complex carbohydrates (at least 45 grams) at bedtime on evenings of vigorous exercise. He developed severe hypoglycemia several hours after playing basketball for 3 hours, drinking, and not eating before bedtime. Vigorous exercise depletes the muscles' glycogen stores. Although his blood glucose level was 163 mg/dL (9.0 mmol/L) just before he went to bed, his muscles continued to extract glucose from the blood for several hours to replenish their glycogen stores. The alcohol in his system inhibited the liver's ability to release glucose into the blood, and thus his plasma glucose level decreased severely while he was asleep. A substantial snack containing complex carbohydrates before bedtime would have been absorbed over several hours and thereby prevented hypoglycemia.

It is neither reasonable nor necessary to advise a fit young man with diabetes to avoid exercising in the evening.

Even light beer contains enough alcohol to inhibit hepatic glucose output. If he is willing to make the change, he should be advised to drink no alcohol on evenings of vigorous exercise.

Although omitting the insulin aspart dose might be reasonable, stopping both forms of insulin would be a poor choice. Doing so would cause his plasma glucose level to increase because of hypoinsulinemia. His plasma glucose level most likely would be extremely high by bedtime and even higher the following morning.

Key Point

  • In a patient with diabetes mellitus, vigorous exercise should be followed by consumption of complex carbohydrates to avoid hypoglycemia, especially when the exercise occurs in the evening.