Obesity Hypoventilation Syndrome and Haematocrit levels: predictor for mortality?

Background: The connection between obstructive sleep apnea and secondary erythrocytosis is controversial. We hypothesized that there could be a higher prevalence of erythrocytosis in patients with Obesity hypoventilation syndrome due to persistent hypoxemia. Methods: We undertook a retrospective, cross-sectional review of OHS patients forming part of an established cohort of “Non -invasive ventilation “patients at the Department of Sleep Medicine at the Royal Infirmary Medical Centre, Edinburgh (2004-2017). We obtained the relevant clinical data from patient9s records. Results: The cohort comprised 74 OHS patients. Overall there were 44 men (59.5 %) and 30 women (40.5%). The mean age at diagnosis was 54 yrs. (25-75 SD 10). The mean Haematocrit level for the group overall was 0.44, in men the mean Hct was 0.45 and 0.41 in women.  Eleven patients had erythrocytosis (14.9%), seven were men and 4 were women. Thirteen patients (17.5%) died during follow- up (2004-2017). There was a statistically significant increase in risk of death in patients with higher and lower haematocrit levels compared to OHS patients with normal haematocrit. Conclusions: To our knowledge, this is the first study showing increased prevalence of erythrocytosis in OHS patients. We found a “U” shape correlation with mortality according to haematocrit levels.