Introduction: This study aimed to determine whether predialysis blood gases is affected by altitude differences in hemodialysis patients with arteriovenous fistulas living in Turkey at three different altitudes. Methods: Patients' predialysis blood gases were compared by standardizing both arterial blood gases collections and working methods for patients undergoing hemodialysis using a dialysate with the same properties at altitudes of 30 m (sea level), 1020 m (moderate altitude), and 1951 m (high altitude). Findings: Blood gases disorders were detected in 32 (82.1%) high altitude group patients, whereas 49 (74.2%) sea level group patients had no blood gases disorders (P < 0.001). pH values in the high altitude group were significantly lower than those in the other groups, and the pH increased as altitude decreased (P < 0.001). The partial pressure of carbon dioxide (PaCO2) values was higher in the sea level group than in the other groups and increased at lower sea levels (P < 0.001). Bicarbonate values were significantly higher in the sea level group than in the other groups and increased at lower sea levels, similar to PaCO2 values (P < 0.001). The partial pressure of oxygen (PaO2) values in the high altitude and sea level groups were significantly higher and increased at lower sea levels (P < 0.001). The oxygen saturation (SaO2) values were significantly lower in the high altitude group than in the other groups and increased gradually at lower sea levels (P < 0.001). Discussion: Predialysis metabolic acidosis was more pronounced in patients undergoing hemodialysis at high altitudes, whereas PaCO2, PaO2, and SaO2 values were lower.