Pneumologie 2015; 69 - P22
DOI: 10.1055/s-0035-1551924

An asymptomatic swiss army professional with an oxygen saturation of 75% – a case report

S Guler 1, S Brunner-Agten 2, S Bartenstein 1, HU Bettschen 3, T Geiser 1, P Keller 4, M Funke 1
  • 1Department of Pulmonary Medicine, University Hospital of Bern, Switzerland
  • 2Institut für Labormedizin, Kantonsspital Aarau, Switzerland
  • 3Lungenpraxis Spiez, Switzerland
  • 4Department of Hematology, University Hospital of Bern, Switzerland

Case report:

We report on a 51 year old man referred for severe nocturnal oxygen desaturation revealed during investigation for suspected sleep apnoea due to daytime sleepiness. The former smoker, known for an allergic bronchial asthma, denied other respiratory or cardiac symptoms. Physical examination was unremarkable. Small airway obstruction was present in pulmonary function test (FEV1 89% pred./MEF50 66% pred.). Pulse oximetry at ambient air showed a peripheral O2 saturation of 75% that increased to 86% under 7 L/min O2. Directly measured oxygen saturation (SaO2) by arterial blood was slightly decreased (89%), with normal pO2 (82 mmHg or 10.9 kPa) and pCO2 (38 mmHg or 5.1 kPa). Calculated p50 was increased to 40 mmHg or 5.3 kPa indicating a low oxygen binding affinity to hemoglobin. Laboratory analysis showed no anemia (hemoglobin 138 g/l), but discretely elevated reticulocytes (2.2%, 107 G/L absolute) and no markers of hemolysis (LDH, bilirubin, haptoglobin). Due to the discrepancy between pO2, invasive and non-invasive measured SO2 we further evaluated for an abnormal hemoglobin. Conventional hemoglobin electrophoresis and high pressure liquid chromatography (HPLC) revealed no conclusive results. However after Sanger sequencing of the beta globin gene, a heterozygous mutation of c.137C>T was detected, indicating a hemoglobin variant called Hemoglobin Cheverly.

Discussion and Conclusion:

Known causes of decreased SpO2 are poor peripheral perfusion, skin pigment, nail polish, anemia, motion artefacts and interfering ambient light. In rare cases of unexplained low SpO2, variant hemoglobins have to be considered as well.

More than 1000 mutations of the globin chains have been described. The most frequent hemoglobinopathies are thalassemia syndromes, HbS, HbC and HbE. Hemoglobin Cheverly is an extremely rare hemoglobin variant with only 5 – 9 cases described so far. The mutation (β-45 Phe→Ser) results in an unstable hemoglobin that can cause mild hemolytic anemia (Yaeger et al., 1983). An abnormal absorbtion spectrum of a variant haemoglobin has to be suspected if SpO2 is lower than SaO2. A reduced O2 affinity of the variant haemoglobin is present if p50 is elevated. In our case Hb Cheverly reveals both of this abnormal characteristics. Analysis by electrophoresis and HPLC might not be sufficient to detect all cases of variant hemoglobins. In face of inconclusive results, genetic sequencing should be performed. Hb Cheverly is not expected to cause symptoms, if no hemolysis is present. Counselling of the affected individuals and equipping them with emergency cards can avoid major diagnostic and therapeutic efforts in case of routine medical interventions or medical emergencies.