Judging disease activity in rheumatoid arthritis by serum free kappa and lambda light chain levels

Abstract

The study aimed to evaluate the levels of serum free kappa (κ) and lambda (λ) light chains in patients with rheumatoid arthritis (RA) as well as exploring the association between serum free κ and λ light chains and activity of RA. For this purpose, healthy individuals and patients with active RA and RA in remission were enrolled, and their serum levels of free κ and λ light chains were measured using rate nephelometry. The diagnostic accuracy of serum free κ and λ light chains was evaluated by receiver operating characteristic curves and 95% confidence intervals for areas under the curve (AUC). The results obtained indicated that the levels of serum free κ and λ light chains in patients with active RA were significantly higher than those of patients in remission and of healthy controls (p < 0.05). Further, the AUC values in patients with active RA were 0.871 for free κ light chain and 0.781 for free λ light chain. When the optimal cut-off point for serum κ light chain was 8.02 g/L, the maximum sensitivity and specificity were 82.5% and 82.5%, respectively, and when the optimal cut-off point for serum λ light chain was 3.57 g/L, the maximum sensitivity and specificity were 80% and 82.5%, respectively. It was thus found that serum levels of free κ and λ light chains were positively correlated with disease activity in RA, the Disease Activity Score 28 (DAS28), and values for C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), platelet count (PLT), rheumatoid factor (RF), and anticitrullinated protein antibody (ACPA) (p < 0.05). In conclusion, high serum levels of free κ and λ light chains in patients with active RA are closely correlated with disease activity parameters including DAS28, CRP, ESR, PLT, RF, and ACPA. Thus, the above-mentioned levels of serum free κ and λ light chains may be used as important indicators of activity of RA.

Keywords: Disease activity; Disease activity score; Light chain; Rheumatoid arthritis.

Figure 1

Serum levels of free κ and λ chain (g/L) in patients with active rheumatoid arthritis (RA), patients in remission, and healthy controls.

Figure 2

The κ:λ chain ratio in patients with active rheumatoid arthritis (RA), patients in remission, and healthy controls.

Figure 3

Receiver operator curves of diagnostic parameters for active rheumatoid arthritis. When the optimal cut‐off point for serum κ light chain was 8.02 g/L, the maximum sensitivity and specificity were 82.5% and 82.5%, respectively (area under the curve 0.871, p < 0.01). However, when the optimal cut‐off point for serum λ light chain was 3.57 g/L, the maximum sensitivity and specificity were 80% and 82.5%, respectively (area under the curve 0.781, p < 0.01).

Figure 4

Analysis of correlation between serum free κ (A) and λ (B) light chains and Disease Activity Score 28 (DAS28). Linear correlation analysis shows that serum free κ and λ light chain levels were positively correlated with DAS28 score in patients with active rheumatoid arthritis (r = 0.774 and 0.665, respectively; p < 0.05).