Carbon Monoxide (CO): What Your Result Means

What is Carbon Monoxide (CO)?

Carbon monoxide (CO) is an odorless, colorless gas that binds hemoglobin far more tightly than oxygen, starving the body of oxygen. The blood test measures carboxyhemoglobin (the percentage of hemoglobin carrying CO). Because CO poisoning can be life-threatening and its symptoms are easily mistaken for flu, testing is critical when exposure is suspected.

Typical reference interval: Normal levels are low — nonsmokers commonly under 2-3%, while smokers can run higher (up to around 10%) from chronic exposure. Symptomatic poisoning generally involves higher levels; any suspected exposure with symptoms is treated as an emergency regardless of the number.. Laboratories differ — the interval printed on YOUR report always governs.

If your Carbon Monoxide (CO) is high

Common reasons Carbon Monoxide (CO) runs above the reference interval:

• Faulty heating or cooking appliances — gas furnaces, water heaters, and stoves can leak CO — a leading cause of home poisoning
• Car exhaust or generators — running engines in enclosed spaces, including attached garages, raises exposure fast
• Smoke inhalation from fires — fires produce CO as a major toxic component
• Smoking — cigarettes deliver CO, so smokers have chronically higher levels
• Occupational exposure — forklift and furnace work in enclosed spaces can expose workers

If your Carbon Monoxide (CO) is low

Common reasons Carbon Monoxide (CO) runs below the reference interval:

• No exposure — a low level is the expected outcome for most people — the reassuring result
• Non-smoker status — people who do not smoke generally run very low
• Recent exposure timing — CO clears over hours once exposure ends, so timing of the test matters

Symptoms worth knowing

Carbon monoxide poisoning causes headache, dizziness, nausea, confusion, and fatigue — symptoms easily mistaken for the flu. Severe poisoning brings loss of consciousness and can be fatal. Because it is odorless, people often do not realize they are being exposed.

What usually happens next

1. If CO poisoning is suspected, get to fresh air and call emergency services immediately — this is a medical emergency, not a wait-and-see result
2. Treatment is high-flow oxygen, sometimes in a hyperbaric chamber, guided by medical professionals
3. Find and fix the source — a qualified technician should inspect appliances, and CO detectors should be installed

Frequently asked questions about Carbon Monoxide (CO) results