The effect of altitude change on anemia treatment response in hemodialysis patients.

Hemodialysis patients who live at high altitude use less exogenous erythropoietin but achieve higher hematocrit levels than those living at a lower altitude. The authors hypothesized that the effect of altitude would be strongest in hemodialysis patients with poor anemia treatment response. To explore this hypothesis, they studied anemia-related outcomes in US hemodialysis patients who move to higher altitudes. Using Medicare and US Geological Survey data, in 1992-2004 they identified instances in which a patient moved from a dialysis center at an altitude of <2,000 feet (600 m) to one at a higher elevation. Of these moves, 5,274 were ≥3,000 feet (900 m; the altitude group) and 25,345 were 250-500 feet (75-150 m; the control group). Among patients with poor treatment response at baseline, large increases in hematocrit and decreases in erythropoietin dosing were observed in the altitude relative to the control group. At 6 months, hematocrit had increased more in the altitude group (5.1%, 95% confidence interval (CI): 4.1, 6.2 vs. 3.7%, 95% CI: 3.5, 3.9), and erythropoietin dosing decreased more (4,600 units/week, 95% CI: 500, 8,700 vs. 1,700 units/week, 95% CI: 1,000, 2,400). No effect of altitude was observed in patients with better treatment response at baseline. These results support the hypothesis that altitude-induced hypoxia reduces erythropoietin requirements in hemodialysis patients with treatment-refractory anemia.