Serum Growth Arrest-Specific Protein 6 Levels are a Reliable Biomarker of Disease Activity in Systemic Lupus Erythematosus

Purpose Growth arrest-specific protein 6 (Gas6) has been suggested to be a biomarker of disease activity in patients with systemic lupus erthematosus (SLE). We investigated the clinical significance of this protein in Korean SLE. Methods Blood samples were collected from 150 SLE patients and 50 normal controls (NC). In addition, follow-up samples were collected from 50 SLE patients. Results Serum Gas6 levels of SLE patients (43.01 + 28.02 ng/mL) were higher than those of NC (20.15 + 9.23 ng/mL, p<0.001). When evaluated sensitivity and specificity of the Gas6 for diagnosing SLE using ROC curves, the sensitivity and specificity were 72.7 % and 84 % with a cut-off value of 25.3 ng/mL. In the ROC analysis of Gas6, anti-dsDNA antibody, ESR, complement 3 and complement 4 to identify patients with active lupus, area under the curve (AUC) of Gas6 was highest with 0.763. Serum Gas6 levels were significantly higher in the patients with serositis (70.04 +/- 30.85 ng/mL) and renal disorder (65.66 +/- 32.28 ng/mL) compared to those without (41.88 +/- 27.44 ng/mL, p=0.033, 40.3 +/- 26.33 ng/mL, p=0.001, respectively). Gas6 levels were correlated positively with anti-dsDNA antibody (r=0.199, p=0.015), ESR (r=0.204, p=0.013) and SLEDAI (r=0.512, p<0.001). In addition, serum Gas6 levels were correlated negatively with hemoglobin (r=-0.165, p=0.043), lymphocyte count (r=-0.165, p=0.043), complement 3 (r--0.343, p<0.001) and complement 4 (r--0.316, p<0.001). Furthermore, change in serum Gas6 levels was correlated with change in SLEDAI levels in the SLE patients that were followed up (r-0.524, p<0.001). Conclusion These results suggest that serum Gas6 can be a reliable clinical marker for monitoring disease activity and treatment response in SLE.