Demographics, clinical features, and comorbidities of high-altitude polycythaemia: a multicentre, retrospective, observational study

Background: High altitude polycythaemia (HAPC) has posed a major burden due to its high prevalence and multisystem involvement among highlanders, but clinical data on HAPC is scarce. We aimed to describe the clinical characteristics of patients with HAPC in China. Methods: Adult patients diagnosed with HAPC in five hospitals of China between August 2012 to May 2024 were retrospectively enrolled. We analysed information including demographics, living altitude, haemoglobin concentration (Hb) and comorbidities, and fitted restricted cubic splines models with multivariable adjustments to investigate the relationship between age, altitude and Hb. Results: A total of 1098 HAPC patients were included and 97 individuals of them did not provide information on ethnicity. Of the remaining 1001 participants, 93% were native Tibetans. The median Hb showed a significant difference (P < 0.0001) between male (21.9 g/dL, interquartile range (IQR) = 21.4-22.9 g/dL) and female patients (19.6 g/dL, IQR = 19.2-20.8 g/dL), and was slightly higher in Tibetans than Han migrants, especially in females (19.6 g/dL, IQR = 19.2-20.7 g/dL vs. 19.3 g/dL, IQR = 19.2-19.5 g/dL) (P = 0.198). Restricted cubic splines models revealed Hb exhibited a positive linear correlation with altitude (P-overall = 0.027, P-nonlinear = 0.291), with a rate of 0.3g/dL/1000 m of elevation, whereas no significant relationship with age (P-overall = 0.974, P-nonlinear = 0.860). The commonest comorbidities were hypertension (18.5%) and pneumonia (17.6%). Besides, heart failure (P < 0.001), chronic airway disease (P = 0.018) and pulmonary heart disease (P < 0.001) were more prominent in females while liver disease (P = 0.079) was more frequent in males. Conclusions: This study suggests a much higher proportion of HAPC in native Tibetans, and the Hb in HAPC patients remains significant gender-specific and altitude-dependent variations. Moreover, in addition to hypertension and pneumonia, gender-specific comorbidity surveillance should pay attention to digestive system disease in male HAPC patients and cardiopulmonary system disease in female HAPC patients.