Acute methemoglobinemia- Diagnosing and managing in family practice.

Methemoglobinemia is a rare but serious disorder in which hemoglobin is oxidized to methemoglobin, impairing oxygen transport. This condition can present in primary care with cyanosis and oxygen desaturation and is potentially misdiagnosed as respiratory or cardiac failure. We present the case of a 38-year-old male driver who was brought to the emergency department unconscious, with cyanosis, and unresponsive to oxygen therapy. His oxygen saturation was 86% on pulse oximetry, although arterial blood gas analysis showed a normal partial pressure of oxygen. The source of poisoning was unknown at the time of admission. Subsequent co-oximetry testing revealed elevated methemoglobin (MtHb) levels (64.8%), confirming a diagnosis of methemoglobinemia. Immediate treatment with intravenous methylene blue resulted in a prompt clinical recovery, with a return to consciousness and normalization of methemoglobin levels within hours. This case highlights the importance of considering methemoglobinemia in patients presenting with unexplained unconsciousness and cyanosis. Early diagnosis and treatment, even when the source of poisoning is unclear, are key to preventing complications and improving patient outcomes.