Table 3. Association of combined urine IL-6 and serum CRP measures with radiographic progression of RA at 3 years.

Categories based on IL-6 and C-reactive protein*	Odds ratio† (95% confidence interval)	Stratified by ACPA‡ Odds ratio† (95% confidence interval)		Stratified by ESR§ Odds ratio† (95% confidence interval)
		Positive n = 121	Negative n = 52	Elevated n = 102	Normal n = 71
Both low (n = 23)	1	1	1	1	1
Both mid (n = 62)	1.4 (0.5–3.7)	1.9 (0.6–5.9)	1.1 (0.1–8.9)	0.9 (0.2–3.7)	2.0 (0.5–7.7)
High C-reactive protein (n = 31)	3.7 (1.2–12.1)	2.5 (1.9–8.6)	2.3 (0.2–18.2)	3.2 (0.6–16.7)	2.7 (0.4–16.4)
High interleukin-6 (n = 26)	4.5 (1.3–16.4)	4.5 (1.1–18.7)	4.5 (0.3–32.6)	2.9 (0.5–17.2)	6.4 (1.0–33.2)
Both high (n = 31)	4.6 (1.4–15.2)	5.0 (1.2–20.6)	7.5 (0.5–22.7)	6.7 (1.0–25.8)	2.0 (0.4–11.2)

ACNPA, anti-cyclic citrullinated antibody; ESR, erythrocyte sedimentation rate.

^*Both low (reference): IL-6 level below the first tertile (<29.9) and C-reactive protein level below the first tertile (<0.2 mg/dL); both mid: mid-range values of C-reactive protein or IL-6, but neither high; high C-reactive protein: high C-reactive protein level only (C-reactive protein >1.5 mg/dL); high IL-6: high IL-6 level only (IL-6 > 116.9); both high: both IL-6 and C-reactive protein levels in the highest tertile (IL-6 ≥ 116.9 and C-reactive protein ≥1.5 mg/dL). IL-6 levels were adjusted for urine creatinine and expressed as units [(ng/mL)/(mg/dL)]×1000.

^†Adjusted for age, sex, smoking status, disease duration, disease activity scores in 28 joints, use of methotrexate, and use of anti-tumor necrosis factor therapy.

^‡The positive cut-off value for ACPA was >5.0 U/mL.

^§The positive cut-off values were as follows: ESR for men >(age/2) mm/hour and ESR for women was >[(age + 10)/2] mm/hour.