[Sex-specific hemoglobin thresholds for oxygen saturation: A non-linear regression analysis based on Tibetan...

To investigate the complex association between hemoglobin levels and resting pulse oxygen saturation (SpO₂) among surgical inpatients in a high-altitude environment, and to define precise, gender-specific physiological adaptation thresholds for hemoglobin, thereby providing evidence-based reference values for health management strategies in high-altitude populations.

This cross-sectional study enrolled adult inpatients from People's Hospital of Xizang Autonomous Region (altitude: 3 650 m) between January 2023 and October 2024. To rigorously evaluate the relationship between hemoglobin and resting SpO₂, multivariate linear regression analysis was performed. Furthermore, restricted cubic spline models and likelihood ratio tests were utilized to explore potential non-linear threshold effects. Models were adjusted for potential confounding factors, including age, body mass index, hypertension, diabetes, smoking, alcoholism, and comorbid pulmonary diseases.

A total of 3 083 inpatients were enrolled in the final analysis, comprising 1 450 males and 1 633 females. The restricted cubic spline analysis revealed a significant non-linear relationship between hemoglobin levels and SpO₂ for the total population (non-linear test, P=0.006), indicating a distinct turning point in the dose-response curve. Two-piecewise linear regression models subsequently identified distinct inflection points for each sex. For female inpatients, the hemoglobin threshold was determined to be 15.482 g/dL; Above this level, SpO₂ significantly decreased as hemoglobin increased (β=-0.477, 95%CI: -0.760 to -0.193, P=0.001). Similarly, for male inpatients, the threshold was identified at 17.288 g/dL; Exceeding this value resulted in a significant inverse correlation between hemoglobin and SpO₂ (β=-0.344, 95%CI: -0.550 to -0.138, P=0.001).

This study establishes specific hemoglobin thresholds for oxygenation status in hospitalized patients at high altitude: 15.482 g/dL for females and 17.288 g/dL for males. Beyond these cut-off values, further increases in hemoglobin are associated with a deterioration in SpO₂, suggesting a transition from physiological adaptation to maladaptive hemoconcentration. These findings highlight the necessity of sex-stratified hemoglobin monitoring and potential preoperative optimization in high-altitude health management to prevent hypoxia-related complications.