Hb M-Saskatoon: An unusual cause of cyanosis in a Spanish child

Pulse oximetry in a 15-month-old boy with cyanosis revealed low oxygen saturation (SpO2 60%) with normal echocardiography findings. Arterial blood gas analysis showed normal PaO2, low hemoglobin oxygen saturation, and high methemoglobin level. Blood analysis revealed mild hemolytic anemia. HPLC and electrophoresis showed a variant hemoglobin in the A2-window and C/E band respectively. Beta-globin gene sequencing revealed heterozygous hemoglobin M Saskatoon [Beta63 (E7) His > Tyr; HBB: c 190C > T] along with alpha + heterozygous thalassemia. Hemoglobins M are structural variants that stabilize heme iron in the oxidized (ferric) state. They can be confused with other causes of methemoglobinemia like genetic alterations in methemoglobin reductase enzyme systems of red cells. The prognosis is excellent in these non-life-threatening conditions. : HbM, a variant of hemoglobin, should be considered in the differential diagnosis of cyanosis and pseudo-cyanosis (brown coloration), once cardiorespiratory pathologies are ruled out. Keywords: Methemoglobinemia, Hemoglobin M, Pulse oximetry, Hemoglobin oxygen saturation, Pseudo-cyanosis