Symptomatic Methemoglobinemia at a Relatively Low Methemoglobin Level After Aniline Exposure in a Patient With Hemoglobin D Trait

Methemoglobinemia is a condition in which hemoglobin is oxidized, impairing its ability to bind and transport oxygen, leading to tissue hypoxia. We report a rare case of symptomatic methemoglobinemia in a patient with a previously undiagnosed hemoglobin D (Hb D) trait, who developed symptoms at a relatively low methemoglobin (MetHb) level following exposure to aniline. A 57-year-old male who works in a garment shop presented to the emergency department with chest pain, dyspnea, and low oxygen saturation unresponsive to high-concentration oxygen therapy. A discrepancy between arterial oxygen partial pressure (pO₂) and oxygen saturation (sO₂) raised suspicion for methemoglobinemia, which was confirmed by an elevated MetHb level of 11.3%. Hemoglobin electrophoresis revealed the presence of the Hb D trait. The patient's recent handling of newly purchased blue jeans in a poorly ventilated stockroom implicated aniline dye as the likely cause of his methemoglobinemia. Treatment with methylene blue (MB) and ascorbic acid resulted in rapid clinical improvement and normalization of MetHb levels. This observation raises the possibility that Hb D may lower the MetHb level at which symptoms develop, a hypothesis that warrants further investigation.