Ricardo AmaruJosef T. PrchalDaniela PatónMireya CarrascoEmma MancillaVictor R. Gordeuk2026-03-222026-03-22202410.1182/blood-2024-204118https://doi.org/10.1182/blood-2024-204118https://andeanlibrary.org/handle/123456789/76096Bolivian Andean Aymara highlanders have been living at 4000 meters for 14,000 years, and have developed evolutionary genetic adaptations to hypoxia (PMID:28448578; PMID:29100088; PMID:36980912). These include EGLN1 encoding prolyl hydroxylase 2 (PHD2), a regulator of transferrin transcription. Transferrin increases in hypoxia and iron deficiency (PMID: 9242677); contrasting reports indicate that elevated transferrin associates with thrombosis in mice but decreased thrombosis in a congenital disorder of hypoxia-sensing (PMID: 36040436; PMID: 31310728; PMID: 8281634). We analyzed clinical and laboratory data of Andean Aymara patients with High-Altitude Anemia (n=137, mean age 45 years, female gender 79%,) or High-Altitude Erythrocytosis (n=149, mean age 56 years, female gender 30%) with transferrin results in their medical records. Iron deficiency was present in 57% of anemia and 23% of erythrocytosis patients. Mean (SD) transferrin concentration was 3.08 (1.25) g/L in anemia and 3.34 (0.84) g/L in erythrocytosis patients. Thrombosis history was present in 8% of anemia and 13% of erythrocytosis patients. In logistic regression analysis in High-Altitude Anemia patients with adjustment for age and gender, iron deficiency associated with increased thrombosis history (odds ratio [OR] 6.7, P=0.030) while higher serum transferrin associated with decreased thrombosis history (OR 0.4, P=0.013). In High-Altitude Erythrocytosis patients iron deficiency associated with increased thrombosis history (OR 5.0, P=0.005), but transferrin's association with thrombosis history was not statistically significant (OR 0.8, P=0.52). In anemia and erythrocytosis patients combined, iron deficiency associated with increased thrombosis history (OR 4.6, P=0.0006) while elevated transferrin associated with reduced thrombosis history (OR 0.62, P=0.038). In individuals with extreme environmental hypoxia, we found no evidence that increasing transferrin is associated with increased thrombosis history, but rather observed a trend to decreased thrombosis history.enThrombosisMedicineEffects of high altitude on humansTransferrinInternal medicinearticle