Treatment decisions for people with non-radiographic axial spondyloarthritis (nr-axSpA) should not be based on a single test for elevated levels of C-reactive protein (CRP), European clinicians say.

Fluctuations are common in CRP results and tests should be repeated after four weeks if they are to be used as a marker of inflammation when determining eligibility to receive DMARD treatment, they recommend in  Arthritis Research and Therapy.

In a study of 106 placebo-treated patients with nr-axSpA they found that half of the patients who were ‘CRP negative’ at baseline went on to have an elevated result (>7.9mg/L) when re-tested over a four-month period.

Of the 26 patients who had normal CRP levels at baseline, 13 went on to have at least one elevated CRP result when tested at two, four, eight, 12 and 16 weeks.

Patients were particularly likely to have an elevated CRP if their initial test was just below (6-7.9 mg/L) the upper limit of normal (ULN).

And of the 80 patients who had a baseline CRP that was elevated, 25 (31%) subsequently had at least one test with normal levels up to 16 weeks later.

Since fluctuations tended to occur over the long term rather than short term,  a repeat test after several weeks would better categorise patients, particularly those with sacroiliitis on MRI and normal CRP, but high disease activity, the researchers said

“ For nr-axSpA patients with no signs of inflammation on MRI and normal CRP levels, in addition to a high disease activity indicative of a potential benefit from anti-TNF treatment, the CRP test should be repeated after at least 4 weeks,” they conclude.

“There is a substantial chance of finding elevated CRP levels upon subsequent testing, thus making the patient eligible for treatment options such as anti-TNF therapies.