American Board of Internal Medicine (ABIM) Certification Practice Exam

What phenomenon is characterized by elevated blood glucose levels in the morning due to rising catecholamines?

1. Dawn phenomenon

2. Somogyi effect

3. Reactive hypoglycemia

4. Glycemic threshold effect

The correct answer is: Dawn phenomenon

The phenomenon characterized by elevated blood glucose levels in the morning due to rising catecholamines is known as the dawn phenomenon. This occurs as part of the body's natural circadian rhythm, where there is an increase in glucose production by the liver and a corresponding decrease in insulin sensitivity during the early morning hours. The surge in hormones such as cortisol, glucagon, and catecholamines (like epinephrine and norepinephrine) prepares the body for waking activities and can lead to higher fasting blood glucose levels upon waking. In contrast to other conditions listed, the dawn phenomenon is not related to prior events of hypoglycemia or other reactive processes. For instance, the Somogyi effect is often confused with the dawn phenomenon; however, it specifically refers to rebound hyperglycemia that occurs after nighttime hypoglycemia, which is driven by physiological counter-regulatory mechanisms responding to low blood sugar. Reactive hypoglycemia involves blood glucose dropping after meals (due to excessive insulin) and is unrelated to the morning glucose levels. The glycemic threshold effect describes the blood glucose concentration level beyond which glucose starts to spill into the urine, which is distinct from the hormonal influences seen in the dawn phenomenon. Thus, understanding the specific mechanisms and time frames involved clarifies why