Polycythemia at Moderate Altitude: Rethinking Screening for Polycythemia Vera

BACKGROUND: Polycythemia is a clinical condition characterized by increased red blood cell mass (RCM). With the aim to increase the sensitivity of capturing patients with polycythemia vera (PV), the hemoglobin (Hb) and hematocrit (Hct) thresholds were lowered in the 2016 revised World Health Organization (WHO) criteria. This study evaluated the impact of the 2016 revised WHO criteria on polycythemia prevalence at moderate altitude and explored the utility of RCM measurement in refining patient selection for PV evaluation at altitude. MATERIALS AND METHODS: Lab records of 62,300 individuals (22,666 residing at an altitude of 2250 meters compared to 39,634 at sea level) were retrospectively analyzed. Polycythemia was defined using Hb and Hct values as Hb >18.5 g/dL (Hct > 54%) in men and Hb > 16.5 g/dL (Hct > 50%) in women (2008 criteria) and Hb >16.5 g/dL (Hct >49%) for men and Hb > 16 g/dL (Hct > 48%) for women (2016 revision). RCM was measured using the carbon monoxide (CO) rebreathing technique in 14 patients referred for polycythemia evaluation and 7 healthy volunteers (HV) with high normal Hb levels. RESULTS: The mean age of participants was 44.6 ± 15.2 years, 50.1% were women, and 36.4% resided at an altitude. Applying the old WHO criteria, polycythemia was identified in 0.96% (121) of women and 2.08% (209) of men at altitude, versus 0.21% (38) in women and 0.45% (94) in men at sea level. The new WHO criteria substantially increased prevalence, especially among men at altitude, with 2.2% (280) of women and 32.5% (3260) of men at altitude meeting the criteria versus 0.44% (82) of women and 9.0% (1901) of men at sea level. Patients residing at altitude who were referred for possible PV did not exhibit a significant difference in RCM in comparison to HV with high normal-range Hb levels. RCM assessment detected patients with elevated RCM despite normal Hb level. CONCLUSION: Revised WHO criteria significantly increased the prevalence of polycythemia at altitude. RCM measurement using the CO rebreathing technique provides valuable diagnostic refinement for patient selection for further Polycythemia evaluation.