Methemoglobinemia in the Era of COVID-19: A Potential Confounder of Glycemic Control

Glycated hemoglobin A(1c) (HbA(1c)) is frequently used as a measure of glycemic control but can be inaccurate in certain clinical scenarios leading to poor estimates of insulin requirements. We present the case of a 76-year-old man with diabetes and COVID infection. HbA(1c) was measured at 5.7%, though the patient reported home glucose readings of 200 to 300 mg/dL (11.1-16.65 mmol/L). Pulse oximetry on presentation was 50% to 60%, which initially improved to 93% with supplemental oxygen of 15 L via nonrebreather face mask. Treatment with remdesivir and dexamethasone was initiated, but the patient was again found to have low oxygen saturations requiring bilevel positive airway pressure and transfer to the intensive care unit. The patient was started on 1.1 U/kg of insulin daily in a basal-bolus regimen. The patient developed severe hyperglycemia requiring 2.4 U/kg to achieve glycemic control. Co-oximeter analysis of an arterial blood gas sample revealed methemoglobinemia. Exchange transfusion was performed with clinical improvement. Subsequent measurement of fructosamine was 360 umol/L (360 000 µmol/L), correlating with reported home glucose measurements. Methemoglobinemia may impair glycation of hemoglobin or interfere with measurement of HbA(1c), thereby compromising the use of this molecule as a marker for glycemic control in patients with this condition.