[U-shaped association between hematocrit and resting pulse oxygen saturation in Tibetan plateau population]

To investigate the relationship between hematocrit (HCT) and low resting oxygen saturation in Tibetan plateau population.

This retrospec-tive cohort study included 3075 Tibetan adult inpatients who underwent elective non-cardiac, non-thoracic surgery at Tibet Autonomous Region People's Hospital between January 2023 and October 2024. Multivariate logistic regression was used to assess the association between HCT and low resting oxygen saturation (SpO₂<88%). Restricted cubic splines were employed to model non-linear relationships, and piecewise logistic regression, in combination with maximum likelihood estimation, was used to identify the HCT threshold.

Multivariate logistic regression analysis showed that elevated HCT was an independent risk factor for low oxygen saturation in the patients. For every 5-percentage-point increase in HCT, the risk of low oxygen saturation increased by 12% (P<0.01). The restricted cubic spline model revealed a significant U-shaped association between HCT and the risk of low oxygen saturation (P<0.01). The HCT threshold for the total population was 42.8%. When HCT was below 42.8%, each 5% increase in HCT was associated with a 22% reduction in the risk of low oxygen saturation in the patients (OR=0.780, 95%CI: 0.619-0.982, P<0.05). When HCT was 42.8% or above, the risk increased by 27.2% (OR=1.272, 95%CI: 1.132-1.429, P<0.01). Stratified analysis indicated that the HCT threshold was 40.4% for female patients and 46.6% for male patients.

There is a U-shaped association between HCT and low resting oxygen saturation in the Tibetan plateau population. An HCT level exceeding the population-specific threshold suggests that the adaptive erythropoietic response to high-altitude hypoxia may transition from being compensatory to potentially detrimental.