A single determination of C-reactive protein does not suffice to declare a patient with a diagnosis of axial spondyloarthritis ‘CRP-negative’

Table 1 Likelihood of finding elevated C-reactive protein (CRP) tests to week 16 after initial tests at baseline

Proportion of subsequent CRP tests elevated	Baseline CRP test normal (n = 26)	Baseline CRP test elevated (n = 80)
0%	13 (50%)	0 (0%)
> 0–20%	1 (4%)	1 (1%)
> 20–40%	4 (15%)	3 (4%)
> 40–60%	4 (15%)	11 (14%)
> 60–80%	1 (4%)	6 (8%)
> 80–100%	2 (8%)	4 (5%)
100%	1 (4%)	55 (69%)

Data included are from weeks 0, 1, 2, 4, 8, 12, and 16. Elevated CRP was defined as CRP > upper limit of normal (7.9 mg/L) and values ≤ 7.9 mg/L were considered normal

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