What to Know About Carboxyhemoglobin Tests

Medically Reviewed by Poonam Sachdev on May 03, 2022
4 min read

A carboxyhemoglobin test is used to diagnose carbon monoxide poisoning. Carbon monoxide binds to hemoglobin — a protein in red blood cells that transports oxygen. Too much carbon monoxide in your blood prevents your body from getting enough oxygen. 

Carbon monoxide poisoning can be deadly. More than 50,000 Americans visit the emergency room for carbon monoxide poisoning annually, and more than 400 people die. A carboxyhemoglobin test can help you get the treatment you need if you’ve inhaled too much carbon monoxide. 

Carbon monoxide is an odorless, colorless gas that can build up in indoor spaces. Carbon monoxide poisoning happens when carbon monoxide builds up to dangerous levels in the blood and prevents your body from getting enough oxygen. Breathing in high levels of carbon monoxide has the potential to become deadly in just a few minutes.

Common sources of carbon monoxide include:

  • Vehicle engines (cars, trucks, boats)
  • Gas stoves
  • Gas and wood-burning fireplaces
  • Fuel-burning appliances such as clothes dryers 
  • Furnaces
  • Gas water heaters
  • Grills
  • Generators
  • Cigarette smoke

Carbon monoxide poisoning can be symptomless or only cause mild symptoms. People who are sleeping, drunk, or otherwise incapacitated can die from carbon monoxide poisoning before they notice any symptoms. Many people with carbon monoxide poisoning describe their symptoms as “flu-like.”

Common symptoms include:

However, unlike the flu, carbon monoxide poisoning does not cause a fever

People at higher risk for carbon monoxide poisoning include infants, pregnant women, the elderly, and people with heart or respiratory disease. 

Certain professions are also at risk of carbon monoxide poisoning at work. Jobs on docks or construction sites and in warehouses, refineries, and boiler rooms may be high risk. People who work with fuel-powered equipment, forges, blast furnaces, engines, or gas lines may also be at higher risk. High-risk professions include:

  • Welders
  • Firefighters
  • Mechanics
  • Forklift operators
  • Highway workers
  • Warehouse workers
  • Public safety officers
  • Diesel engine operators

If you experience symptoms of carbon monoxide poisoning and may have been exposed to high carbon monoxide levels, seek fresh air immediately and visit the emergency room or call 911.

A carboxyhemoglobin test is a blood test to check the amount of carbon monoxide in your blood. Your doctor will use a needle attached to a syringe to collect a blood sample from a vein or artery. Your doctor will send off this blood sample for testing. 

The blood is tested in a machine called a multiple wavelength spectrophotometer. This allows your doctor to measure your carboxyhemoglobin level and determine if you have too much carbon monoxide in your blood. 

The normal range for carbon monoxide in the blood is: 

  • Under 1% for non-smokers in areas with low pollution
  • Under 5% for people who live in urban areas or other areas with high pollution
  • Under 10% for smokers

Carbon monoxide poisoning is generally diagnosed at a carboxyhemoglobin level of over 10%. Severe poisoning occurs at levels over 20%.

A carbon monoxide blood test is the most accurate way to determine carboxyhemoglobin levels. Your doctor may also use a special pulse oximeter called a CO-oximeter. These allow for more accurate oxygen level readings in a patient with carbon monoxide poisoning. Your doctor will also take how long you were exposed to carbon monoxide into account. 

Carboxyhemoglobin tests are blood tests and are very safe.

The primary risks include:

  • Soreness 
  • Bruising
  • Dizziness 

You should not feel any long-term effects from a carboxyhemoglobin test. 

If your carboxyhemoglobin test shows that you have carbon monoxide poisoning, your doctor will determine treatment based on a few factors:

  • How long you were exposed to carbon monoxide
  • How much carbon monoxide you were exposed to
  • What your symptoms are
  • What your carboxyhemoglobin level is

Mild cases of carbon monoxide poisoning can resolve on their own once you start breathing fresh air. Moderate or severe cases may require hospitalization and devices such as an oxygen concentrator or a hyperbaric oxygen chamber. If you can't breathe independently, your doctor will use a ventilator to get you the oxygen you need. 

Carbon monoxide poisoning is avoidable. Following a few tips can help you prevent it.

Use carbon monoxide detectors. Carbon monoxide is colorless and odorless — you can’t see, taste, or smell it. However, a carbon monoxide detector can alert you to high levels of carbon monoxide in an area before the situation becomes dangerous. Check the batteries on your carbon monoxide detector every six months.

Service fuel-burning appliances, fireplaces, and other sources of carbon monoxide regularly. Regular maintenance helps ensure this equipment has no defects or leaks that could expose you to high levels of carbon monoxide. 

Never use grills, camping stoves, generators, or other fuel-powered equipment intended for outdoor use in an enclosed area. Using equipment designed for outdoor use inside or in an enclosed space can cause carbon monoxide to quickly build up to dangerous levels, even if the windows are open.

Never sleep inside an idling vehicle or run a car in an enclosed space. Vehicle engines produce very high levels of carbon monoxide. Hundreds of people die each year from running a car inside an enclosed space like a garage. Carbon monoxide can leak from the exhaust system and enter the cabin of the vehicle while the engine is running.