Archive Of Standardized Exam Questions: Carbon Monoxide Poisoning


This page is dedicated to organizing various examples of standardized exam questions whose answer is carbon monoxide poisoning. While this may seem a odd practice, it is useful to see multiple examples of how carbon monoxide poisoning will be characterized on standardized exams (namely the boards and the shelf exams). This page is not meant to be used as a traditional question bank (as all of the answers will be the same), however seeing the classic “test” characterization for a disease is quite valuable.


When it comes to standardized exams, each condition has its own “code” marked by key buzzwords, lab findings, clues, etc. If you are well versed in this code you will be able to more quickly identify the condition that is being discussed, and get the right answer on the exam you are taking. Below is the “code” for carbon monoxide poisoning

Chief Complaints:

  • Loss of consciousness can be seen in more serious cases.
  • Headache 
  • Dizziness
  • Confusion
  • Nausea 

Patient History:

  • Exposures: smoke inhalation, defective heating systems, motors operating in poorly ventilated areas (such as car in garage)

Clinical Workup: 

  • Red-pink coloration of the skin: carboxyhemoglobin has a bright red color and can turn the lips/skin a red/pink color.
  • Elevated carboxyhemoglobin level will be present in the blood.  

Question # 1

A 50 year old man comes to the office because he has been suffering from daytime headaches. He explains that his head is “killing him” and that he also feels nausea and dizziness. He denies any chest pain , shortness of breath, and does not have a cough. He is a peaceful sleeper, gets 10 hours of sleep every night, and his wife is pleased because he does not snore at night. His past medical history is unremarkable, and the patient does not take any chronic medications. He has a 20 pack year history of smoking cigarettes, and drinks 2 beers every week. He is occupied as a underground parking garage attendant. His vital signs are within normal limits, and his oxygen saturation is 98% on room air. His pulmonary and cardiac exams are within normal limits, except for an apical holosystolic murmur that is heard upon auscultation. His extremities are warm and well perfused, and they show no signs of cyanosis, clubbing, or edema. His neurological exam is unremarkable. Labs are ordered and are shown below:

  • Hematocrit: 62%
  • Platelets: 210,000/mm³
  • Leukocytes: 6,900/mm³

What condition might this patient be suffering from?

Explanation # 1

Headache/nausea/dizziness + exposure to car exhaust (in parking garage) + polycythemia = carbon monoxide poisoning

Question # 2

A group of high school students are having an indoor barbecue on a oil winter night. They are grilling vegetables, chicken, and potatoes. A few hours later they present to the ER with complaints of nausea, vomiting, headaches, and vague abdominal pain. One of the patients is evaluated and has a heart rate of 105 bpm, and a respiration rate of 24/min. The physician notes that his skin has a pinkish hue to it. What is the likely diagnosis?

Explanation # 2

Barbecuing indoors (producing CO) + nausea/headaches + pink skin hue = carbon monoxide poisoning

Question # 3

A 40 year old man is brought to the hospital after collapsing while working in the garage. He was performing some maintenance on his classic car when he lost consciousness. He had been working in the garage with the door partially open, and the engine running. The patient has no chronic medical conditions, and he does not take any chronic medications. What is the likely diagnosis in this patient?

Explanation # 3

Collapse/loss of consciousness + in garage with engine running =  carbon monoxide poisoning

Question # 4

A 50 year old woman comes to the ED with complaints of a headache, dizziness, and she also states that she is “sick to her stomach”. She denies any fever, cough, and does not have a runny nose. She explains that her daughter has also been complaining of a headache. They have a fireplace at home they use to keep warm, and have been using it frequently this winter. The patients vitals are within normal limits, except for some slight tachycardia. A physical exam is non-contributory. What is the most likely diagnosis in this patient?

Explanation # 4

Headache/nausea/dizziness + burning fire indoors = carbon monoxide poisoning

Question # 5

A 10 year old boy is brought to the ER by her father after she loses consciousness. They had been traveling in their truck during the night, and had made a bed for their son in the back of the truck (enclosed with a canopy) so that he could sleep during the drive. Upon arriving at their destination, they noticed that they had difficulty waking him up. Finally when he did wake up, he complained of a very severe headache, and nausea. After he began to vomit they decided to bring him tot he hospital. Currently his pulse is 145 bpm. A physical exam shows bright red skin around the mouth. What is the likely diagnosis in this patient?

Explanation # 5

Loss of consciousness + confinement in truck bed (exposed to exhaust fumes with CO) +  headache/nausea + bright red skin around mouth = carbon monoxide poisoning

Question # 6

A 5 year old girl is brought to the hospital because she has a two hour history of a headache and dizziness. She also complains of nausea and has vomited a few times. A physical exam is remarkable only for lethargy. When her venous blood is collected it appears bright red, and her carboxyhemoglobin saturation is 32% (ref range < 5%). What is the likely diagnosis in this patient?

Explanation # 6

Headache/dizziness/nausea + elevated carboxyhemoglobin saturation = carbon monoxide poisoning


Many questions on standardized exams go beyond simply recognizing the underlying condition. Often there are specific testable facts regarding some aspect of the disease’s pathophysiology/management/clinical implications that are commonly asked. Some of these are listed below:

  • Consequence of poisoning: carbon monoxide has a much higher affinity for hemoglobin compared to oxygen. This results in tissue hypoxia. Without oxygen the last step of the electron transport chain (transfer of electrons to oxygen) is compromised.
  • How is the diagnosis made: by a blood ABG, and detecting high levels of carboxyhemoglobin in the blood.
  • Treatment: 100% oxygen is the typical treatment. Intubation or hyperbaric oxygen therapy may be needed in more severe conditions.
  • Limitations of pulse oximetry: a pulse oximetry can not differentiate between carboxyhemoglobin and oxyhemoglobin (cannot be used in the diagnosis of CO poisoning).


Page Updated: 03.28.2017