Table 3.

Association of RF IgA with High Attenuation Areas and Interstitial Lung Abnormalities on CT

	Rheumatoid Factor IgA Quartile					Percent difference (95% CI) in HAA per doubling of RF IgA	P-value
	< 6.04 U/mL	6.04 to 9 U/mL	9.04 to 15.86 U/mL	> 15.86 U/mL	P-value for trend
No. of subjects	1969	1554	1529	1684
HAA, cm3, median (IQR)	116.6 (99.0 to 142.5)	119.9 (101.7 to 143.0)	123.6 (102.9 to 148.1)	124.5 (105.2 to 149.2)
Percent difference (95% CI) in HAA
Unadjusted	0 (Ref)	1.99 (0.03 to 3.99)	5.15 (3.11 to 7.22)	6.26 (4.25 to 8.30)	<0.001	1.65 (1.10 to 2.21)	<0.001
Adjusted*	0 (Ref)	1.73 (0.15 to 3.33)	2.18 (0.57 to 3.82)	3.25 (1.65 to 4.88)	<0.001	0.95 (0.50 to 1.40)	<0.001
Never smoker	0 (Ref)	1.96 (−0.37 to 4.35)	1.02 (−1.37 to 3.46)	2.58 (0.12 to 5.09)	0.09	0.55 (−0.17 to 1.29)	0.14
Ever smoker	0 (Ref)	1.59 (−0.53 to 3.76)	3.46 (1.29 to 5.69)	4.35 (2.23 to 6.52)	0.001	1.35 (0.78 to 1.92)	<0.001
						Prevalence ratio (95% CI) for ILA per doubling of RF IgA
No. of subjects	747	617	516	523
ILA prevalence, % (95% CI)	9.6 (7.7 to 12.0)	12.5 (10.1 to 15.3)	13.6 (10.9 to 16.8)	16.1 (13.2 to 19.5)
Prevalence ratio (95% CI) for ILA
Unadjusted	1 (Ref)	1.29 (0.96 to 1.75)	1.41 (1.03 to 1.92)	1.67 (1.24 to 2.24)	0.001	1.15 (1.08 to 1.23)	<0.001
Adjusted†	1 (Ref)	1.24 (0.92 to 1.68)	1.26 (0.93 to 1.71)	1.42 (1.05 to 1.91)	0.038	1.11 (1.03 to 1.20)	0.006
Never smoker	1 (Ref)	0.96 (0.60 to 1.51)	0.88 (0.55 to 1.40)	1.15 (0.73 to 1.82)	0.46	1.04 (0.88 to 1.23)	0.68
Ever smoker	1 (Ref)	1.49 (0.99 to 2.22)	1.67 (1.11 to 2.52)	1.62 (1.09 to 2.42)	0.001	1.14 (1.05 to 1.23)	0.001

^*Adjusted for age, sex, race, study site, BMI, waist circumference, pack-years of smoking, current smoking status, total volume of imaged lung, percent emphysema, and tube current

^†Adjusted for age, sex, race, pack-years of smoking, and current smoking status

^**P-value for interaction of RF IgA and smoking was 0.15 in the HAA analysis and 0.31 in the ILA analysis.