Zhenghai S, et al. - Osteoarthritis patients exhibited a significantly higher level of serum AXL compared with that in the healthy controls. Serum AXL was identified to be closely associated with the severity of radiographic osteoarthritis.

• This study involved 183 patients with knee osteoarthritis and healthy volunteers (n = 170).

• Using enzyme-linked immunosorbent assay, AXL level in serum was recorded.

• The osteoarthritis group, vs controls, had significantly higher serum AXL levels.

• Elevation in serum AXL level was noted in association with the increase of Kellgren-Lawrence score, in osteoarthritis cases.

• Positive correlation of serum AXL level with the following was observed: age, body mass index, erythrocyte sedimentation rate, serum C-reactive protein, cartilage oligomeric protein, matrix metalloproteinase-13, and transforming growth factor-β1 levels.

• By receiver operating curve analysis, 33.375 ng/mL was identified as the cut-off value for serum AXL.