Scavenger receptor-A is a sensitive disease activity biomarker in ESR and CRP normal rheumatoid arthritis

Identification of rheumatoid arthritis (RA) patients in active disease with normal ESR and CRP is a challenge in disease activity assessment. The objective of this study was to evaluate the performance and clinical significance of Scavenger receptor-A (SRA) as a disease activity biomarker in RA, especially in ESR and CRP normal patients.

One hundred and sixty-two RA (40 discovery cohort; 122 validation cohort), 20 osteoarthritis (OA), and 36 healthy controls (HCs) were recruited. Ten disease activity markers were evaluated by Bio-Plex Pro Human Cytokine Assay in the discovery cohort. SRA levels were measured by enzyme-linked immunosorbent assay (ELISA) in the validation cohort. The association between SRA and clinical phenotypes was also analyzed. ROC analysis was performed for disease activity prediction.

SRA was found to be correlated with disease activity in the discovery cohort. The serum SRA level was verified by ELISA in the validation cohort, and was found to be correlated with disease activity index in RA patients, including DAS28-ESR (r = .477, p < .001), swollen joint counts, and tender joint counts; as well as inflammation markers, including ESR and CRP. In ESR and CRP normal RA, there was a strong correlation between SRA and DAS28-ESR ( $$  = 4.564, p = .003). In addition, area under the ROC of SRA was higher than AUC_ESR and AUC_CRP in ESR and CRP normal RA patients, suggesting that serum SRA could be more sensitive than ESR and CRP for disease activity assessment in this group of patients. In the low DAS28-ESR (≤3.2) group, the AUC of SRA for disease activity measurement was higher than that of ESR and CRP, indicating that SRA was also more sensitive than ESR and CRP in low-disease activity RA.

SRA was correlated with RA disease activity and may be a sensitive serum biomarker for disease activity evaluation, especially in ESR and CRP normal patients, as well as in the low-disease activity group. SRA could be a promising marker for disease activity assessment.