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Abstract
Background Interleukin 6 (IL-6) has a crucial role in the pathogenesis of rheumatoid arthritis (RA) [1]. Measurement of serum and plasma IL-6 level has been reported that is useful for monitoring of RA disease activity [2-3]. In contrast, it still take a few hours to measure serum IL-6 level using traditional methods, and cause limitation for measuring it as routine assessment in daily clinical setting.
Objectives We established high sensitivity IL-6 quick measure system. We investigated accuracy of the system in RA patients.
Methods Serum samples were collected from 70 patients fulfilling the ACR classification criteria for RA. Serum IL-6 levels can be measured by our current system using 100 μl whole blood in only 25 minutes. Measurement of serum IL-6 level by chemiluminescent enzyme immunoassay (CLEIA) employed a two-step sandwich method using a cartridge for IL-6 measurement developed specifically for the fully automated chemiluminescent enzyme immunoassay system (Lumipulse f, Fujirebio, Tokyo) used at our clinical laboratory. The lower detection limits for serum IL-6 were 5pg/ml in our system and 0.1pg/ml in CLEIA. We first examined the correlation between our system and CLEIA methods. Secondary, we compared both system IL-6 titers and clinical parameter (CRP, ESR, DAS28-CRP, DAS28-ESR, CDAI and SDAI). Pearson's correlation coefficients were used to assess whether the ranking of each IL-6 was similar between methods. Associations between clinical measures and serum IL-6 levels were assessed using Spearman's rank correlation test. A value of p<0.05 was considered statically significant.
Results Seventy patients were analyzed, and their mean age was 65.8 (18-83), 59 (84.3%) patients were female. 43 (61.4%) patients were used MTX and the mean dose was 7.44 mg/week. 18 (25.7%) patients were treated by biological agents (ETN: 10, IFX: 3, ABA: 3, ADA: 1). Figure 1 shows a correlation between the data measured by our system and CLEIA. The IL-6 level measured by our system positively correlated with IL-6 level measured by CLEIA. The correlation of our system (x) with CLEIA (y) for IL-6 was: y=0.895x-5.94, r=0.966 (p<0.0001). Serum IL-6 level in our system correlated significantly with CRP (r=0.497, P<0.001), ESR (r=0.478, P<0.001), DAS28-CRP (r=0.278, P<0.05) and DAS28-ESR (r=0.327, P<0.01), but did not correlate with CDAI (r=0.114, P=0.35) and SDAI (r=0.209, P=0.08). Serum IL-6 level in CLEIA correlated significantly with CRP (r=0.682, P<0.001), ESR (r=0.534, P<0.001), but did not correlate with DAS28-CRP (r=0.163, P=0.17), DAS28-ESR (r=0.229, P=0.06), CDAI (r=-0.034, P=0.78) and SDAI (r=0.089, P=0.46).
Conclusions Our cytokine quick measure system has accuracy as good as CLEIA methods. Serum IL-6 level can be measured in 25 minutes using our methods. It might be usable for daily clinical setting and contributes to RA treatment.
References
McInnes IB, Schett G. The pathogenesis of rheumatoid arthritis. N Engl J Med 365 (23):2205-19.
Naoshi Nishina, Yuko Kaneko, Hideto Kameda et al. Reduction of plasma IL-6 but not TNF-α by methotrexate in patients with early rheumatoid arthritis: a potential biomarker for radiographic progression. Clin Rheumatol (2013) 32: 1661-66.
Keiko Shimamoto, Tomoki Ito, Yoshio Ozaki et al. Serum Interleukin 6 before and after therapy with Tocilizumab is a principal biomarker in patients with rheumatoid arthritis. J Rheum 40(7):1074-81.
Disclosure of Interest K. Koyama: None declared, K. Matsuda Grant/research support: Toray, H. Haro: None declared
DOI 10.1136/annrheumdis-2014-eular.2017