Table 4

Estimated difference in BASDAI or ASDAS-CRP drop after initiation of a first TNF inhibitor between smokers (ever, current, previous) and non-smokers

Smokers vs non-smokers with elevated baseline CRP
	Difference in ΔBASDAI				Difference in ΔBASDAI
	BASDAI units	95% CI	p Value		BASDAI units	95% CI	p Value
Ever smokers	0.62	0.13 to 1.11	0.01	Current smokers	0.75	0.22 to 1.28	0.005
Ever smokers	0.62	0.13 to 1.11	0.01	Past smokers	0.36	−0.28 to 1.00	0.27
	Difference in ΔASDAS-CRP				Difference in ΔASDAS-CRP
	ASDAS units	95% CI	p Value		ASDAS units	95% CI	p Value
Ever smokers	0.55	0.19 to 0.90	0.002	Current smokers	0.69	0.30 to 1.08	0.001
Ever smokers	0.55	0.19 to 0.90	0.002	Past smokers	0.30	−0.18 to 0.78	0.22
Smokers vs non-smokers with normal baseline CRP
	Difference in ΔBASDAI				Difference in ΔBASDAI
	BASDAI units	95% CI	p Value		BASDAI units	95% CI	p Value
Ever smokers	0.43	−0.05 to 0.90	0.08	Current smokers	0.30	−0.24 to 0.83	0.28
Ever smokers	0.43	−0.05 to 0.90	0.08	Past smokers	0.59	0.002 to 1.18	0.05
	Difference ΔASDAS-CRP				Difference in ΔASDAS-CRP
	ASDAS units	95% CI	p Value		ASDAS units	95% CI	p Value
Ever smokers	0.15	−0.20 to 0.49	0.40	Current smokers	0.17	−0.21 to 0.56	0.38
Ever smokers	0.15	−0.20 to 0.49	0.40	Past smokers	0.12	−0.31 to 0.54	0.59

Effect size estimates of differences in ΔBASDAI and ΔASDAS as demonstrated in figure 1C,D are displayed for patients treated with their first TNFi in subgroup analyses by baseline CRP status. Models are adjusted for gender, age, symptom duration, human leucocyte antigen-B27, classification as ankylosing spondylitis versus non-radiographic axial spondyloarthritis, body mass index, educational level and physical exercise and for differences in baseline BASDAI or ASDAS and BASFI. Positive coefficients signify a reduced TNF response in terms of BASDAI and ASDAS drop in comparison to never smokers. Separate models are used to investigate the smoking status as either ever or never and the smoking status as either current, previous or never. The full model results for the subgroup analysis of TNF patients with elevated baseline CRP are shown in the online supplementary table S1.
ASDAS-CRP, Ankylosing Spondylitis Disease Activity Score using C-reactive protein (CRP); BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; p, Wald-type p value; TNFi, tumour necrosis factor inhibitor.