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Journal of Peking University (Health Sciences) ›› 2026, Vol. 58 ›› Issue (1): 196-200. doi: 10.19723/j.issn.1671-167X.2026.01.026

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

Zhuoma GONGJUE1, Yiting MAO1, Puzhen DAWA1, Ciren LABA1, Qi YAN1,2,*()   

  1. 1. Department of Anesthesiology, People's Hospital of Xizang Autonomous Region, Lhasa 850002, China
    2. Department of Anesthesiology, Peking University People's Hospital, Beijing 100044, China
  • Received:2025-08-12 Online:2026-02-18 Published:2026-01-05
  • Contact: Qi YAN
  • Supported by:
    Peking University People's Hospital Research and Development Funds(RDJP2022-68); Peking University People's Hospital Research and Development Funds(RDE2022-21); Beijing Resident Standardized Training Quality Improvement Project(2023011); Xizang Autonomous Region Natural Science Foundation Group Medical Aid Project(XZ2024ZR-ZY013(Z))

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Abstract:

Objective: 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. Methods: 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. Results: 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). Conclusion: 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.

Key words: Oxygen saturation, Hemoglobin, Altitude, Threshold effect, Health management

CLC Number: 

  • R339.54

Table 1

Baseline characteristics by sex in Tibetan inpatients"

Variables Total (n=3 083) Male (n=1 450) Female (n=1 633) P
Age/years, $\bar x \pm s$ 45.0±14.6 47.3±14.1 43.0±14.7 < 0.001
BMI/(kg/m2), $\bar x \pm s$ 23.8±4.2 23.5±4.0 24.1±4.4 < 0.001
Hypertension, n(%) 275 (8.9) 107 (7.4) 168 (10.3) 0.005
Diabetes, n(%) 46 (1.5) 26 (1.8) 20 (1.2) 0.194
Smoking history, n(%) 441 (14.3) 419 (28.9) 22 (1.3) < 0.001
Alcoholism, n(%) 503 (16.3) 408 (28.1) 95 (5.8) < 0.001
Comorbid pulmonary disease, n(%) 1 505 (48.8) 729 (50.3) 776 (47.5) 0.127
Hemoglobin/(g/dL), $\bar x \pm s$ 15.5±2.5 16.8±2.1 14.4±2.2 < 0.001
SpO2 at rest/%, M (P25, P75) 90.0 (88.0, 91.0) 90.0 (88.0, 91.0) 90.0 (88.0, 91.0) 0.121
SpO2 at rest<88%, n(%) 615 (19.9) 268 (18.5) 347 (21.2) 0.055

Table 2

Multivariable linear regression analysis of the association between hemoglobin and pulse oxygen saturation at rest in Tibetan female and male inpatients"

Items Crude coefficient (95%CI) Crude P value Adjusted coefficient (95%CI) Adjusted P value
Female -0.141 (-0.211 to -0.066) < 0.001 -0.081 (-0.149 to 0.004) 0.038
Male -0.184 (-0.255 to -0.113) < 0.001 -0.124(-0.202 to -0.047) 0.002

Figure 1

Non-linear association between hemoglobin and SpO2 at rest in Tibetan female (A) and male (B) inpatients Adjusted for age, body mass index, hypertension, diabetes, smoking history, alcoholism, comorbid pulmonary disease. The solid red curve depicts the fitted non-linear association, with the surrounding shaded area representing the 95% confidence interval. The lower panel displays the histogram of hemoglobin concentration distribution within the sample. SpO2, pulse oxygen saturation."

Table 3

Threshold effect analysis of hemoglobin on pulse oxygen saturation at rest in Tibetan inpatients"

Gender Hemoglobin n Coefficient (95%CI) P value
Female < 15.482 g/dL 1 164 -0.021 (-0.121, 0.080) 0.688
≥15.482 g/dL 469 -0.477 (-0.760, -0.193) 0.001
Likelihood ratio test < 0.001
Male < 17.288 g/dL 904 0.032 (-0.099, 0.163) 0.634
≥17.288 g/dL 546 -0.344 (-0.550, -0.138) 0.001
Likelihood ratio test < 0.001
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