Soluble interleukin-18 receptor complex is a novel biomarker in rheumatoid arthritis

Table 1 Characteristics of rheumatoid arthritis (RA) patients and control participants^a

Participant characteristics	Control (n= 67)	RA (n= 145)	AOSD (n= 6)	OA (n= 31)	SLE (n= 39)
Mean age, yr (± SEM)	60.7 ± 2.1	56.7 ± 1.2	54.3 ± 9.9	76.3 ± 1.5^b	38.8 ± 2.1^b
Sex, n
Male	40	24^b	1^b	6^b	6^b
Female	27	121	5	25	33
Smoking status, n
Nonsmoker	37	32	1	0	0
Smoker	30	12	0	0	0
Unknown	0	101	5	31	39
Joint damage^c, n
I	ND	42	ND	ND	ND
II	ND	47	ND	ND	ND
III	ND	20	ND	ND	ND
IV	ND	36	ND	ND	ND
Functional classification^d, n
I	ND	24	ND	ND	ND
II	ND	92	ND	ND	ND
III	ND	29	ND	ND	ND
IV	ND	0	ND	ND	ND
Mean DAS28 (CRP) (± SEM)	ND	4.3 ± 0.1	ND	ND	ND
Mean DAS28 (ESR) (± SEM)	ND	4.9 ± 0.1	ND	ND	ND
Mean HAQ (± SEM)	ND	5.8 ± 0.7	ND	ND	ND
Mean WBC (cell count/μL) (± SEM)	ND	7,307.3 ± 211.0	8,950.0 ± 533.1	5,134.7 ± 304.8	ND
Mean CRP level, mg/dL (± SEM)	ND	2.27 ± 0.22	2.15 ± 1.14	0.08 ± 0.02	ND
Mean ESR, mm/hour (± SEM)	ND	45.0 ± 2.7	40.3 ± 18.6	ND	ND
RF-positive^d, n (%)	2/64 (3.1%)	106/145 (73.1%)	0/6 (0%)	2/30 (6.7%)	2/39 (5.1%)
Mean RF, U/mL (± SEM)	3.7 ± 1.3	158.0 ± 20.9 ^b	4.8 ± 2.7	5.4 ± 1.3^b	3.8 ± 1.0
CCP-positive^e, n (%)	0/59 (0%)	121/145 (83.4%)	1/6 (16.7%)	0/30 (0%)	3/39 (7.7%)
Mean CCP, U/mL (± SEM)		0.3 ± 0.1	261.5 ± 27.2^b	22.5 ± 22.3	0.5 ± 0.1^b
PSL, n (%)	ND	89/145 (61.4%)	ND	ND	ND
Mean dose, mg/day (± SEM)	ND	5.91 ± 0.32	ND	ND	ND
MTX, n (%)	ND	58/145 (40.0%)	ND	ND	ND
Mean dose, mg/week (± SEM)	ND	6.87 ± 0.34	ND	ND	ND
DMARDs^f, n (%)	ND	117/145 (80.7%)	ND	ND	ND

^aRA = rheumatoid arthritis; AOSD = adult-onset Still's disease; OA = osteoarthritis; SLE = systemic lupus erythematosus; DAS28 = 28-joint Disease Activity Score; HAQ = Health Assessment Questionnaire; WBC = white blood cell; CRP = C-reactive protein; ESR = erythrocyte sedimentation rate; RF = rheumatoid factor; CCP = anticyclic citrullinated peptide antibody; PSL = prednisolone; MTX = methotrexate; DMARDs = disease-modifying antirheumatic drugs; ^bP < 0.05 vs. healthy controls; ^cSteinbrocker global score (I to IV) [21]; ^cSteinbrocker functional classification was used, ranging from class I, "complete functional capacity to carry out all usual duties without handicaps," to class IV, "largely or wholly incapacitated with (the person) bedridden or confined to wheelchair" [21]; ^dcutoff serum concentration of the immunoglobulin M rheumatoid factor (RF) is 20 units/mL; ^ecutoff serum concentration of the anti-CCP antibody is 4.5 U/mL; ^fnone of RA patients were treated with tumor necrosis factor α inhibitor at this point.

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