Table 2: The clinical manifestation of methemoglobinemia [1, 2].

%MetHgbSymptomology

0–3Asymptomatic and normal level in blood
3–15Possibly asymptomatic, grayish pallor, mild cyanosis, and low oxygen saturation per pulse oximeter
15–20Cyanosis and chocolate-brown appearance of blood
20–50Dyspnea, fatigue, weakness, headache, dizziness, and syncope
50–70CNS depression, lethargy, seizures, and metabolic acidosis
>70Severe cyanosis and death