Oxygen Saturation in Pulse Oximetry in Hemoglobin Anomalies

Abstract

Pulse oximetry is an essential diagnostic method in pediatric emergency medicine and pediatric intensive care. However, if undetected hemoglobin anomalies are the underlying cause measurements of low oxygen saturation can be interpreted incorrectly or may lead to unnecessary examinations. In 2 recently discovered hemoglobin anomalies, Hb Bonn and Hb Venusberg, this resulted in extensive and repeat cardiopulmonary examinations. This review aims to provide an overview of hemoglobin anomalies causing low oxygen saturation.We describe the methods required for differential diagnosis of hemoglobin anomalies, such as hemoglobin electrophoresis, High Performance Liquid Chromatography, hemoglobin gene sequencing and spectral photometry, and the difficulties with the interpretation of results. Furthermore, with a review of the literature we provide an extensive overview of hemoglobin anomalies which result in low oxygen saturation measurement in pulse oximetry. With the examples of Hb Bonn, a novel hemoglobin mutation of the proximal α1-globin, which results in false low pulse oximetry measurements of oxygen saturation, and Hb Venusberg, a low oxygen-affine hemoglobin mutation of the β-globin, we highlight the difficulties arising from the respective case histories.In pediatric medicine, hemoglobin anomalies must be included in the diagnosis as a possible underlying cause of low oxygen saturation in case of ambiguous or conflicting pulse oximetry findings.

How we diagnose and manage altered oxygen affinity hemoglobin variants

“…Examples of such Hbs include Hb Bassett, Hb Rothschild and Hb Canebiere . There are also a subset of low affinity variants with low SpO 2 and normal SaO 2 (eg, Hb Titusville and Hb Bonn) . Variants with this unusual pattern have falsely low SpO 2 measurements due to abnormal absorption spectra of the variant Hb at wavelengths emitted by the pulse oximeter.…”

Oxygen Saturation of 75%, but No Symptoms!

“…In general, small amounts of COHb and MetHb are not detected by pulse oximetry and lead to overestimation of SpO 2 , if present [4]. Variant hemoglobins are rare causes of falsely low pulse oximetry readings and are usually taken into consideration only after extensive assessment for respiratory and cardiac diseases, exclusion of MetHb, SulfHb, COHb, and other factors disturbing the performance of pulse oximeters [5]. …”

A novel haemoglobin variant mimicking cyanotic congenital heart disease

“…Mutations in the β-globin gene (HBB) will only become clinically significant months after birth 14. Hb variants known to have low SpO 2 measurements are listed in figure 1 8…”

“…Hb variants clinically significant in newborns appear in italics. Reprinted from Zur et al 8. Reprinted with permission.…”

“…If PaO 2 is normal, an Hb assessment should be made, including electrophoresis, high-performance liquid chromatography and isoelectric focusing. In the presence of an abnormal Hb variant, DNA sequence analysis is necessary to identify and characterise the mutation 8 18 19…”