A composite serum biomarker index for the diagnosis of systemic sclerosis interstitial lung disease: a multicentre, observational, cohort study

OBJECTIVE: In patients with systemic sclerosis (SSc), we investigated composite serum biomarker panels for the diagnosis and risk-stratification of SSc-associated interstitial lung disease (SSc-ILD). METHODS: Twenty-eight biomarkers were analysed in 640 participants: 259 with SSc-ILD and 179 SSc-controls without ILD (Australian Scleroderma Cohort Study), 172 idiopathic pulmonary fibrosis (IPF)-controls (Australian IPF Registry), and 30 healthy controls. A composite index was developed from biomarkers associated with ILD in multivariable analysis derived at empirical thresholds. Performance of the index to identify ILD, and specifically SSc-ILD, and its association with lung function, radiological extent, health-related quality of life (HRQoL) were evaluated in derivation and validation cohorts. Biomarkers to distinguish SSc-ILD from IPF-controls were identified. RESULTS: A composite biomarker index, comprising SP-D, Ca15-3 and ICAM-1, was strongly associated with SSc-ILD diagnosis, independent of age, sex, smoking and lung function (index=3: pooled adjusted OR 12.72, 95%CI 4.59-35.21, p<0.001). The composite index strengthened the performance of individual biomarkers for SSc-ILD identification. In SSc patients, a higher index was associated with worse baseline disease severity (index=3 relative to index=0: adjusted absolute change in FVC% - 17.84% and DLCO% - 20.16%, both p<0.001). CONCLUSION: A composite serum biomarker index, comprising SP-D, Ca15-3 and ICAM-1 may improve the identification and risk-stratification of ILD in SSc patients at baseline