CHEST Guidelines-A-37-Year-Old-Man-With-Bronchial-Asthma-and-Unexpl

A-37-Year-Old-Man-With-Bronchial-Asthma-and-Unexpl

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A 37-year-old man with a history of bronchial asthma was presented with persistent hypoxemia and a saturation gap, despite normal clinical parameters and test results. He displayed breathlessness and wheezing, which were managed with bronchodilators and glucocorticoids, but his oxygen saturation remained abnormally low at 75-80%. Diagnostic tests including chest radiographs, spirometry, ECG, and CT scans were unremarkable. Arterial blood gas analysis showed normal oxygen levels, but oximetry revealed a significant saturation gap.<br /><br />Further investigation with high-performance liquid chromatography (HPLC) and genetic testing revealed a rare variant of hemoglobin called Hemoglobin Cheverly, which presents with a leftward shift on the HPLC chromatogram, and Sanger sequencing confirmed a heterozygous missense mutation in the beta-globin gene. Hb Cheverly is a low-oxygen affinity hemoglobin variant causing erroneous pulse oximetry readings due to differential light absorption characteristics similar to deoxygenated hemoglobin.<br /><br />Common with about 1,000 known hemoglobin variants, Hb Cheverly can remain undetected because it doesn't typically cause significant anemia or hemolysis. In the presented case, the patient and his asymptomatic siblings exhibited an increased saturation gap due to this genetic condition. The variant's presence, while not life-threatening, necessitates awareness to avoid unnecessary diagnostic or emergency procedures, as it does not correlate with actual tissue hypoxemia.<br /><br />This case underscores the importance of comprehensive diagnostic measures when faced with unexplained hypoxemia and highlights the potential for rare hemoglobin variants to affect pulse oximetry readings without indicative clinical symptoms. Proper clinical evaluation requires awareness of such genetic anomalies and appropriate counseling for affected individuals and their families.

Keywords

bronchial asthma

hypoxemia

saturation gap

Hemoglobin Cheverly

pulse oximetry

HPLC

beta-globin mutation

oxygen affinity

genetic testing

clinical evaluation