Carboxyhemoglobin Level Interpretation
Reads a co-oximetry carboxyhemoglobin level against a baseline.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Carboxyhemoglobin measured by co-oximetry
- 24 percent
- Loss of consciousness at any point
- Yes
- Oxygen already running when the sample was drawn
- High-flow oxygen
- Hours on oxygen before the sample
- 1 hours
- Pulse oximeter reading, which does not measure carboxyhemoglobin
- 99 percent
Result: 24 percent, above the non-smoker baseline of about 3 percent
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Up to about 3 percent
- The non-smoker baseline. A level within it does not exclude poisoning, because oxygen given before the sample brings it down quickly.
- Up to about 10 percent
- The smoker baseline. The same 8 percent that confirms exposure in a non-smoker may be no more than baseline in a smoker.
- Above baseline
- Confirms exposure. It does not grade it.
- The level and severity
- Carboxyhemoglobin does not correlate with the severity of poisoning and does not predict outcome. A modest level in someone who lost consciousness is still a serious poisoning.
- What escalation rests on
- Loss of consciousness, a neurologic finding, cardiac ischemia, pregnancy, or symptoms persisting on oxygen. Hyperbaric oxygen is considered on these, not on the number.
- The pulse oximeter
- Cannot tell carboxyhemoglobin from oxyhemoglobin and reports the sum, so the saturation reads normal or high however severe the poisoning is.
- Against methemoglobin
- The opposite failure. There the oximeter plateaus low; here it reads falsely high.
- Half-life
- About 4 to 5 hours on room air, 60 to 90 minutes on high-flow oxygen, and 20 to 30 minutes hyperbaric. A level drawn after oxygen was started understates the peak.
What you enter
- Carboxyhemoglobin measured by co-oximetry
- Smoker, whose baseline runs up to about 10 percent
- Loss of consciousness at any point
- Any neurologic finding, including confusion
- Cardiac ischemia, arrhythmia, or a raised troponin
- Pregnancy
- Symptoms persisting after high-flow oxygen
- Oxygen already running when the sample was drawn
The other 2 fields
- Hours on oxygen before the sample
- Pulse oximeter reading, which does not measure carboxyhemoglobin
How this is calculated
Weaver LK. Carbon monoxide poisoning. N Engl J Med. 2009;360(12):1217-1225. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.