A 36-year-old man on Levemir (insulin detemir) and Humalog (insulin lispro) measures blood glucose before breakfast and finds it is low. What is the most likely cause?

• A. Levemir dose is too high
• B. Humalog dose is too high
• C. Skipped dinner the previous evening
• D. Exercise overnight increased insulin sensitivity

Answer: (A)

Long-acting insulin provides the background, overnight coverage that keeps hepatic glucose production in check. If the basal insulin dose is too high, it continues to act through the night and suppresses glucose release, so the fasting glucose in the morning drops. The rapid-acting insulin mainly controls post-meal glucose; if it were too high, hypoglycemia would be more likely after meals rather than before breakfast. Skipping a dinner could lower morning glucose too, but with both basal and bolus insulin in use, the most consistent and likely cause of a low pre-breakfast reading is an excessive basal insulin dose.