American Board of Internal Medicine (ABIM) Certification Practice Exam

Which type of alcohol is known to cause an elevated anion gap but a normal osmol gap?

1. Methanol

2. Isopropyl alcohol

3. Ethyl alcohol

4. Butanol

The correct answer is: Isopropyl alcohol

Isopropyl alcohol, also known as isopropanol, is known for causing an elevated anion gap metabolic acidosis without significantly affecting the osmol gap. This is an important distinction in the clinical setting. When isopropyl alcohol is metabolized, it produces acetic acid, which leads to metabolic acidosis. The elevated anion gap results from the accumulation of unmeasured anions (like lactate or acetic acid) in the blood. However, isopropyl alcohol does not contribute significantly to the osmol gap because it is less effective at increasing the osmolarity of the serum compared to other alcohols like methanol or ethylene glycol. In contrast, methanol and ethylene glycol typically result in both an increased anion gap and an increased osmol gap due to their metabolites. Ethyl alcohol, which is common in beverages, also does not typically produce the same clinical presentations as isopropyl alcohol when consumed in the same context. Butanol’s effects differ as well. Understanding these distinctions is crucial for the proper diagnosis and management of patients with suspected alcohol intoxication.