Korelasi antara kadar serum secreted frizzled-related protein-1 (SFRP-1) dan tumor necrosis factor-alpha (TNF-alpha) dengan penanda turnover tulang pada pasien artritis reumatoid perempuan premenopause = Correlation of secreted frizzled-related protein-1 (SFRP-1) serum and tumor necrosis factor-alpha (TNF-alpha) serum with bone turnover markers in patients with rheumatoid arthritis in premenopausal women