Affinity pediatrics
If these appear abnormal, protein testing and globin DNA sequencing can help to establish the genetic mutation and diagnosis these are necessary for future genetic counseling. Often, no clinically significant downstream effects are present when Hb has low oxygen affinity, and no treatment of hypoxemia or mild anemia is required.ĭiagnosis of oxygen affinity-altering genetic mutations in Hb first requires determination of the Hb-oxygen dissociation curve and P50 value, the oxygen tension at which Hb is 50% saturated. Notably, although pulse oximetry shows low peripheral oxygen saturation, oxygen delivery to the peripheral tissues is actually increased the oximeter is simply detecting the relatively low percentage of oxygenated Hb in the bloodstream in the setting of increased oxygen extraction by peripheral tissues. Variants with low oxygen affinity, including Hb Kansas, Hb Beth Israel, Hb Saint Mande, and Hb Sunshine Seth, may result in anemia, cyanosis, and low peripheral oxygen saturation. Hb variants with high oxygen affinity, including Hb Chesapeake, Hb Montefiore, and Hb Crete, often result in erythrocytosis and no clinically significant downstream effects. Genetic mutations in Hb structure that alter its affinity for oxygen may or may not be clinically significant. In contrast, if Hb affinity for oxygen is reduced, oxygen delivery to peripheral tissues increases this change may result in relative anemia, because fewer red blood cells are required for adequate oxygen delivery, and the patient may have cyanosis due to increased oxygen extraction by peripheral tissues. More red blood cells are required to compensate for poor oxygen delivery, resulting in erythrocytosis. If Hb affinity for oxygen is increased, oxygen adheres tightly to Hb and oxygen delivery to peripheral tissues is impaired. Genetic mutations in these chains can affect the affinity of Hb for oxygen. Normal adult hemoglobin (Hb) is composed of a tetramer of 2 α-globin and 2 β-globin chains. In the absence of cardiopulmonary pathologic conditions, other causes, such as hemoglobinopathies associated with low oxygen affinity, should be considered. Low peripheral oxygen saturation in newborns can be due to cardiac or pulmonary disease. This case report describes Hemoglobin Sunshine Seth, a rare low-oxygen-affinity hemoglobin variant presenting as reduced peripheral oxygen saturation in an otherwise well-appearing infant male. These changes may or may not be of clinical significance.
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Mutations in the structure of alpha- and beta-globin chains can alter the affinity of hemoglobin for oxygen, and changes in oxygen affinity may result in changes in the oxygen saturation detected by pulse oximetry. Therefore, it is important to consider alternative, albeit rare, diagnoses, including hemoglobinopathies with abnormal oxygen binding properties.
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When this evaluation is unrevealing, other interventions may be tried without clear benefit to the patient, including, but not limited to, supplemental oxygen. The diagnostic evaluation for neonatal hypoxemia can be invasive and expensive.
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The differential diagnoses for reduced peripheral oxygen saturation in an infant include congenital heart disease, respiratory distress syndrome, transient tachypnea of the newborn, persistent pulmonary hypertension of the newborn, meconium aspiration syndrome, pneumonia, pneumothorax, and sepsis.
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Pulse oximetry is routinely used in the newborn nursery for clinical monitoring and to detect critical congenital heart disease.