Out of the Blue: Cyanosis and Methemoglobinemia in a Renal Transplant Patient Following Phenazopyridine Ingestion.

Methemoglobinemia is a rare but serious condition affecting the blood's ability to carry oxygen. Symptoms at presentation are often nonspecific. We describe the case of a 58-year-old female presenting with unexplained central cyanosis and severe hypoxia despite preserved respiratory effort and seemingly reassuring lab values. Further questioning revealed recent ingestion of a large quantity of phenazopyridine, an over-the-counter urinary analgesic known to cause oxidative stress. Co-oximetry confirmed significant elevation of methemoglobin levels. Methylene blue is well-regarded as the gold standard, and its use in treatment of this patient led to favorable clinical and laboratory improvement. Clinicians must maintain a high index of suspicion for dyshemoglobinemias in patients with unexplained cyanosis refractory to oxygen therapy, particularly when conventional metrics of oxygenation are inconsistent with the overall clinical picture.