Table 2

Univariable analysis of factors associated with serum NN and NA levels in patients with SLE
Variable Category/term Ratio for NN (95% CI) P-value for NN Ratio for NA (95% CI) P-value for NA
Gender * Female (n = 336) 1 1
Male (n = 61) 2.01 (1.06, 3.81) 0.03 5.00 (2.50,9.98) <0.001
Disease duration Ratio given per 5-year increase 0.43 (0.23, 0.79) 0.005 0.32 (0.20,0.51) <0.001
Age (at diagnosis) Ratio given per 10-year increase 0.10 (0.02, 0.46) <0.001 0.04 (0.01,0.16) 0.002
Ethnicity* Caucasian (n = 182 ) 1 1
Afro-Caribbean (n = 146 ) 0.75 (0.47, 1.22) 2.07 (1.26,3.40)
Other (n = 69) 0.33 (0.17, 0.63) 0.003 3.75 (1.86,7.56) <0.001
Any ENA** No (n = 165) 1 1
Yes (n = 232) 3.43 (2.19, 5.37) <0.001 3.19 (1.93,5.27) <0.001
Anti-Ro** No (n = 226) 1 1
Yes (n = 171) 1.70 (1.12, 2.59) 0.01 1.81 (1.14,2.89) 0.01
Anti-La** No (n = 345) 1 1
Yes (n = 52) 0.79 (0.41, 1.50) 0.47 0.46 (0.20,1.06) 0.07
Anti-Sm** No (n = 298) 1 1
Yes (n = 99) 5.63 (3.66, 8.67) <0.001 6.25 (3.84,10.2) <0.001
Anti-RNP** No (n = 288) 1 1
Yes (n = 109) 1.08 (0.69, 1.70) 0.74 1.72 (1.06,2.79) 0.03
Anti-dsDNA level <50 IU/ml (n = 177) 1 1
≥50 IU/ml (n = 170) 0.76 (0.26, 1.13) 0.17 1.32 (0.66,2.65) 0.43
C3 level <0.9 g/l (n = 139) 1 1
≥0.9 g/l (n = 208) 0.83 (0.57, 1.20) 0.32 1.26 (0.86,1.87) 0.24
Disease activity in general system§ A, B (n = 31) 1 1
C, D, E (n = 344) 0.96 (0.60, 1.54) 0.87 1.19 (0.71,2.00) 0.52
Disease activity in mucocutaneous system A, B (n = 41) 1 1
C, D, E (n = 334) 0.99 (0.63, 1.56) 0.95 1.32 (0.76,2.29) 0.33
Disease activity in neuropsychiatric system A, B (n = 18) 1 1
C, D, E (n = 357) 0.56 (0.13, 2.38) 0.44 1.04 (0.50,2.19) 0.91
Disease activity in musculoskeletal system A, B (n = 47) 1 1
C, D, E (n = 328) 1.20 (0.47, 3.04) 0.71 0.68 (0.43,1.05) 0.08
Disease activity in cardiorespiratory system A, B (n = 13) 1 1
C, D, E (n = 362) 0.43 (0.24, 0.78) 0.006 1.40 (0.22,8.70) 0.72
Disease activity in vascular system A, B (n = 12) 1 1
C, D, E (n = 363) 0.33 (0.17, 0.63) 0.001 0.39 (0.19,0.82) 0.01
Disease activity in renal system A, B (n = 41) 1 1
C, D, E (n = 329) 1.09 (0.40, 2.97) 0.86 4.28 (2.13,8.58) <0.001
Disease activity in hematological system A, B (n = 95) 1 1
C, D, E (n = 280) 1.21 (0.84, 1.74) 0.30 1.44 (0.95,2.17) 0.08
Overall disease activity over last four assessments Persistently low (n = 166) 1 1
Persistently mod/high (n = 209) 0.91 (0.66, 1.25) 0.57 0.66 (0.47,0.92) 0.01
Hydroxychloroquine No (n = 223) 1 1
Yes (n = 174) 3.52 (2.40, 5.17) <0.001 3.21 (2.08,4.95) <0.001
Immunosuppression No (n = 200) 1 1
Yes (n = 197) 1.66 (1.17, 2.34) 0.004 1.33 (0.89,1.98) 0.16
Oral corticosteroids ≤7.5 mg/day (n = 101) 1 1
>7.5 mg/day (n = 296) 0.81 (0.59, 1.13) 0.22 1.00 (0.69,1.44) 0.99
Albumin Ratio given per 5 g/l increase 1.38 (1.20,1.59) <0.001 1.42 (1.22,1.65) <0.001

*For gender, n values refer to the numbers of samples taken from female and male subjects, rather than the numbers of females and males in the cohort of patients. A similar stipulation applies to ethnicity where n values refer to the number of samples taken from patients of each ethnic group.

For the complex associations with disease duration and age, we carried out analysis of both linear and squared terms. The figures in the table refer to linear terms. The ratios for squared terms for NN are 0.66 (95% CI: 0.51, 0.85) for disease duration and 1.56 (95% CI: 1.20, 2.03) for age. The ratios for squared terms for NA are 0.59 (95% CI: 0.46, 0.75) for disease duration and 1.72 (95% CI: 1.32, 2.24) for age.

**For ENA, anti-Ro, anti-La and anti-Sm we did not have results from the date of every sample but it is assumed that positivity and negativity for these antigens generally remain stable.

§“Disease activity in general system” refers to the BILAG score (A, B, C, D or E) in the General Category of the BILAG index on the day when each sample was taken. The same principle applies to the remaining organ systems listed in the table, which are the eight different categories recorded in BILAG. Bold type indicates statistically significant P-values (P <0.05).

Croca et al.

Croca et al. Arthritis Research & Therapy 2014 16:R48   doi:10.1186/ar4477

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