The level of full-length phospho-OPN in synovial fluid of seropositive (mean ROD 0.200±0.018, median 0.198) and seronegative (mean ROD 0.192±0.027, median 0.194) RA patients was higher when compared to the levels of OA patients (mean ROD 0.153±0.017, median 0.149), no significant difference between seropositive and seronegative group was seen, as shown in Fig 1A. Here, SPP1 is linked to rheumatoid arthritis.