American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the correlation of blood glucose increase with serum sodium levels?

1. Every 50 mg/dL increase decreases sodium by 1.0 mEq/L

2. Every 100 mg/dL increase decreases sodium by 2.0 mEq/L

3. Every 100 mg/dL increase decreases sodium by 1.6 mEq/L

4. Every 150 mg/dL increase decreases sodium by 1.2 mEq/L

The correct answer is: Every 100 mg/dL increase decreases sodium by 1.6 mEq/L

The correct answer reflects the established relationship between blood glucose levels and serum sodium levels, often referred to in the context of hyperglycemic states such as diabetes mellitus. When blood glucose levels rise, this increase can cause a relative dilution of sodium due to fluid shifts and osmotic effects. Specifically, for every 100 mg/dL increase in blood glucose, it is understood that sodium levels can decrease by approximately 1.6 mEq/L. This correlation is based on the principle that hyperglycemia leads to osmotic diuresis, resulting in a dilutional effect on sodium. In practice, this relationship is important to consider when interpreting serum sodium levels in patients with elevated blood glucose, as it helps clinicians avoid misdiagnosing hyponatremia in the context of hyperglycemia. The other options suggest different rates of sodium decrease with glucose levels, which do not align with the well-documented literature on the topic. The discrepancies in those rates reflect a misunderstanding of the physiological principles at play, highlighting the importance of recognizing the specific correlation of 1.6 mEq/L for every 100 mg/dL increase in blood glucose. Understanding this correlation is crucial in clinical settings, especially when managing patients with diabetes or acute hyperglycemic crises