Haematocrit level in obesity hypoventilation syndrome: a predictor of mortality?

Background: The connection between obstructive sleep apnea and secondary erythrocytosis is controversial. We hypothesised that there may be a higher prevalence of erythrocytosis in patients with obesity hypoventilation syndrome (OHS) due to persistent hypoxemia.

Methods: The study was a retrospective, cross-sectional review of patients with OHS derived from an established cohort of "non-invasive ventilation" patients at the Department of Sleep Medicine at the Royal Infirmary Medical Centre, Edinburgh (2004-2017). Relevant clinical data were obtained from patient records.

Results: The cohort comprised 74 patients with OHS, 44 men (60%), mean age at diagnosis 54 ± 10 years. The mean haematocrit level for the group overall was 0.44, in men 0.45, and in women 0.41. Of 11 patients with erythrocytosis (15%), 7 were men. Thirteen patients (18%) 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 that in patients with OHS who had normal haematocrits.

Conclusions: This is the first study showing increased prevalence of erythrocytosis in OHS patients. There was a "U"-shaped correlation with mortality according to haematocrit levels.