[From persistent "hypoxemia" to the diagnosis of an hemoglobinopathy]

Low oxygen (O2) affinity hemoglobin (Hb) variants are a group of structural hemoglobinopathies, caused in most cases by point mutations in beta or alpha globin genes. The clinical presentation is widely variable, from asymptomatic patients to those presenting cyanosis and/or low O 2 saturation without signs of chronic hypoxia. Accurate identification of these patients is essential to avoid invasive cardiorespiratory procedures that could be unnecessary. We present the case of a girl in an acute viral illness context, with repeated low peripheral O2 saturation (SpO2) readings without clinical picture of hypoxemia. The differential diagnosis included a low O 2 affinity Hb, suspected by an increased partial pressure of O2 at 50% (p50) and confirmed by molecular biology. We highlight the usefulness of arterial blood gas analysis and the p50 determination in the initial phase of evaluation of an unexplained "hypoxemia".