American Board of Internal Medicine (ABIM) Certification Practice Exam

Which diagnostic test is essential for confirming carbon monoxide poisoning?

1. Chest X-ray

2. Carboxyhemoglobin measurement

3. Pulse oximetry

4. Blood gas analysis

The correct answer is: Carboxyhemoglobin measurement

Carboxyhemoglobin measurement is the essential diagnostic test for confirming carbon monoxide poisoning because it specifically quantifies the amount of carbon monoxide bound to hemoglobin in the blood. This test measures the percentage of hemoglobin that is in the form of carboxyhemoglobin, which is crucial for diagnosis, as carbon monoxide has a much higher affinity for hemoglobin than oxygen does. While other tests such as pulse oximetry and blood gas analysis provide useful information about a patient's oxygenation and acid-base status, they are not definitive for diagnosing carbon monoxide poisoning. Pulse oximetry can give falsely normal readings in cases of carbon monoxide poisoning because it may not differentiate between oxyhemoglobin and carboxyhemoglobin. Blood gas analysis can provide important insights but does not directly measure carboxyhemoglobin levels. A chest X-ray may be used to rule out other conditions or complications but has no direct role in diagnosing carbon monoxide poisoning. Thus, carboxyhemoglobin measurement stands out as the key test enabling healthcare providers to confirm exposure to carbon monoxide and assess its severity accurately.