Prognostic value of oxygenated hemoglobin (OxyHem) in fibrosing interstitial lung diseases

Background: Progressive hypoxemia is a hallmark of fibrosing interstitial lung disease (fILD). OxyHem is a simple-to-measure correlate of oxygen content. We aimed to assess whether OxyHem correlates with outcomes in fILD. Methods: The database of our center was reviewed for fILDs. OxyHem (g/dL) was calculated as Hb x fractional SaO2. Clinical and functional data with absolute declines of FVC≥10% and/or DLCO≥15% were retrospectively analysed. Predictive values were evaluated by binary logistic and Cox regression analyses with age, gender, BMI, DLCO and FVC as covariates. Results:650 fILD patients (29% IPF, 28.6% cHP, 12.4% iNSIP, 16.3% uILD, 9.2% RA-ILD, 4.3% other ILD; 63.3% male, mean age 68.4 years) were analysed. The mean follow-up period was 16.8 months. Mean FVC was 74.4%pred., and 29.3% of patients showed a FVC decline ≥10%. OxyHem (mean13.4±1.4 g/dL) was strongly related to FVC decline ≥10% (odds ratio 1.33, p=0.0002) and also an independent predictor of the first occurrence of FVC decline ≥10% (hazards ratio [HR] 1.53, p=0.003). No similar relationships were observed for DLCO decline. Mortality was analysed in the IPF subgroup, in which 31/187 patients (16.4%) died. OxyHem Conclusion: OxyHem is an independent predictor of disease progression and outcomes in fILD. Future work has to validate these findings in larger cohorts.