RESUMEN
BACKGROUND: Screening for congenital heart diseases by pulse oximetry is used for the initial assessment of the neonate. Variants of hemoglobin F can compromise light absorbance, inducing erroneous results. CASE REPORT: Two infants screened for congenital heart disease showed an asymptomatic low peripheral oxygen saturation. Arterial blood gases analysis revealed a normal arterial pressure of oxygen and oxygen saturation. More likely and/or severe causes of hypoxemia were ruled out. This "artifact" with SpO2-SaO2 dissociation, and after exclusion of other common etiologies of hypoxemia, raised the clinical suspicion of hemoglobinopathy. Hemoglobin molecular and genetic studies identified specific mutations in gamma chains from hemoglobin F, named hemoglobin F Sardinia. CONCLUSION: Hemoglobin F variants may result in low peripheral oxygen saturation readings by pulse oximetry, explaining the discordance in the clinical appearance and low peripheral oxygen saturation readings.