Table 8.

Relationship between pack-year category and frequency of AS patients in low and high MMP clusters

Pack years	Low MMP cluster	High MMP cluster
0	46 (73.0)	17 (27.0)
1 to 15	19 (52.8)	17 (47.2)
16 to 30	8 (47.1)	9 (52.9)
> 30	5 (35.7)	9 (64.3)a

Data presented as n (%). AS, ankylosing spondylitis; MMP, matrix metalloproteinase. ^aP (trend) = 0.001 (Cochrane-Armitage test for trend).