Erythrocytosis and Previous Deep Vein Thrombosis in Occupationally Active Adult Men Living at Moderate Altitude: A Retrospective Cross-Sectional Study

Objective: Deep vein thrombosis (DVT) is an important cause of venous thromboembolism-associated morbidity and mortality. Chronic exposure to moderate altitude may promote erythrocytosis through adaptive erythropoiesis, whereas elevated low-density lipoprotein (LDL) cholesterol may contribute to endothelial dysfunction and vascular inflammation. This study aimed to determine the frequency of previous DVT and to investigate the association of erythrocytosis and LDL cholesterol with previous DVT in occupationally active adult men living at moderate altitude. Methods: This retrospective cross-sectional study included 200 occupationally active adult men residing at an altitude of approximately 1300–1400 m above sea level. Participants were classified according to the presence or absence of a documented history of previous DVT. Hemoglobin and hematocrit were evaluated as markers of erythrocytosis, whereas LDL cholesterol was evaluated as the principal metabolic variable. Age, smoking status, hypertension, platelet count, white blood cell (WBC) count, red blood cell (RBC) count, and C-reactive protein (CRP) were analyzed as secondary variables. Because of the small number of DVT events and complete separation for hematocrit, univariate Firth-penalized logistic regression was used to identify factors associated with previous DVT. Results: Previous DVT was documented in 7 participants (3.5%). Participants with previous DVT were significantly younger than those without DVT (33.0±5.1 vs. 39.1±8.8 years, p=0.018) and had significantly higher hemoglobin levels (17.83±0.86 vs. 16.88±0.98 g/dL, p=0.027). In univariate Firth-penalized logistic regression, each 1-g/dL increase in hemoglobin was associated with higher odds of previous DVT (odds ratio [OR] 2.94, 95% confidence interval [CI] 1.32–6.71; p=0.009). Elevated hematocrit (≥49%) was present in all participants with previous DVT (100.0% vs. 74.1%). Firth regression provided a finite but highly imprecise estimate for hematocrit ≥49% (OR 5.28, 95% CI 0.62–689.64; p=0.151); the extremely wide CIs reflect sparse events and complete separation. Mean LDL cholesterol levels were similar between groups (122.0±34.3 vs. 121.2±29.6 mg/ dL, p=0.952). Smoking, hypertension, platelet count, WBC count, RBC count, and CRP were not significantly associated with previous DVT (all p > 0.05). Conclusion: A history of previous DVT was identified in 3.5% of this relatively young, homogeneous male population living at moderate altitude. Higher hemoglobin levels were associated with previous DVT in univariate analysis; however, an independent association could not be established because multivariable adjustment, including adjustment for age, was not feasible owing to the small number of events. These findings should therefore be considered exploratory and hypothesis-generating and require confirmation in larger prospective studies.