Aims : Low levels of complement 3 (C3) and 4 (C4) are known to be associated with disease activity in SLE. Recently automated IL-6 test is introduced to clinical laboratories. We aimed to determine the IL-6 and complements (C3, C4, and CH50) to find out the usefulness as monitoring markers for disease activity in SLE.
Methods : Eighty-seven SLE patients were studied. The patients were categorized as three groups according to the levels of C3 and C4 ; a group with normal C3 and C4 (37 patients), decreased C3 and normal C4 (38 patients) and decreased both C3 and C4 (12 patients). Plasma levels of IL-6 and CH50 were measured in those patients with additional healthy subjects. Kruskal-Wallis test was performed among the groups.
Results : Healthy subjects and the three groups (normal C3 and C4, decreased only C3, and decreased both complements) showed the median level of IL-6 less than 1.50, 2.74, 2.12, and 3.04 pg/mL; CH50 were 28.15, 18.65, 18.70, and 6.90 U/mL, respectively. Levels of IL-6 and CH50 showed no statistically significant differences among the patient subgroups. However, the data of all the SLE groups showed higher IL-6 (p < 0.001), and the group with decreased both complement components showed lower CH50 level than healthy subjects (p = 0.05).
Conclusions : In SLE patients, plasma IL-6 levels were significantly increased, and that of CH50 were declined in patients with both C3 and C4 decreased. IL-6 may be a useful marker for differentiation of SLE patients from healthy subjects. Further prospective studies on the usefulness of IL-6 are helpful for SLE disease activity.