Methemoglobin Level Interpretation
Reads a co-oximetry methemoglobin level against published bands.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Methemoglobin measured by co-oximetry
- 18 percent
- Pulse oximeter reading, which does not measure methemoglobin
- 85 percent
- Arterial oxygen tension, which is normal in methemoglobinemia
- 98 mmHg
Result: 18 percent, a level that produces cyanosis
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Under 3 percent
- Within the range seen normally.
- 3 to 15
- Often little more than discoloration.
- 15 to 20
- Cyanosis, with blood that is chocolate-brown and does not redden on exposure to air.
- 20 to 50
- Headache, fatigue, dizziness and breathlessness.
- 50 to 70
- Seizures, arrhythmia, coma and metabolic acidosis.
- Over 70
- Often fatal.
- Methylene blue
- Given for symptoms at any level, or at 30 percent and above without them.
- The pulse oximeter
- Does not measure this. Its reading drifts toward about 85 percent and stops there however high the level climbs, and it does not correct on oxygen.
- The blood gas
- The arterial oxygen tension is normal, because it measures oxygen dissolved in plasma rather than what the hemoglobin can carry. Only co-oximetry measures methemoglobin.
- G6PD deficiency
- Methylene blue works through NADPH from the pentose phosphate pathway, so it does not reduce the methemoglobin and can cause hemolysis.
What you enter
- Methemoglobin measured by co-oximetry
- Symptoms attributable to the methemoglobinemia
- Known G6PD deficiency
- Taking a serotonergic drug
- Pulse oximeter reading, which does not measure methemoglobin
- Arterial oxygen tension, which is normal in methemoglobinemia
How this is calculated
Wright RO, Lewander WJ, Woolf AD. Methemoglobinemia: etiology, pharmacology, and clinical management. Ann Emerg Med. 1999;34(5):646-656. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.