Utility of Repeated C-Reactive Protein Testing Nonradiographic Axial Spondyloarthritis

CRP test
CRP test
Results suggest that C-reactive protein testing should be repeated after at least 4 weeks.

In patients with nonradiographic axial spondyloarthritis (axSpA) with no signs of inflammation on MRI and normal C reactive protein (CRP) levels, as well as high disease activity indicative of potential benefits from tumor necrosis factor inhibitor (TNFi) therapy, CRP testing should be repeated after ≥4 weeks, according to data published in Arthritis Research & Therapy.

The investigators sought to examine the likelihood of a CRP test indicating elevated CRP levels in patients with nonradiographic axSpA who have had a prior normal CRP test. They conducted a post-hoc analysis of data from the phase 3, double-blind, randomized, placebo-controlled RAPID-axSpA study (ClinicalTrials.gov identifier: NCT01087762). The study enrolled patients who were MRI-positive for axSpA or had elevated CRP levels (more than the upper limit of normal, 7.9 mg/L). At 1 week, patients were randomly assigned in a 1:1:1 ratio to placebo, certolizumab pegol (CZP) 400 mg every 4 weeks, or CZP 200 mg every other week. Patients randomly assigned to placebo who did not meet Assessment of Spondyloarthritis International Society 20% response criteria (ASAS20) at either 14 or 16 weeks received either CZP 200 mg every other week or CZP 400 mg every 4 weeks. Moreover, participants who received placebo who did not attain an ASAS20 response were randomly assigned to CZP at 24 weeks.

Participant CRP levels were assessed at baseline and at 9 time points until 24 weeks. Among 106 patients who received placebo with baseline CRP measurements, 25% had normal CRP levels at baseline, of whom 50% had ≥1 test revealing an elevated CRP level to 16 weeks. Among 75% of patients with elevated baseline CRP levels, 31% had ≥1 normal CRP test result to 16 weeks. Based on linear mixed models, no changes in mean CRP levels were revealed in those receiving placebo from baseline to 24 weeks.

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The investigators concluded that in patients with nonradiographic axSpA who have CRP levels less than upper limit of normal, the CRP test should be repeated after ≥4 weeks, as there is a considerable possibility that subsequent testing will reveal elevated CRP levels, which would allow a patient to access treatment options, including TNFi therapies.


Landewé R, Nurminen T, Davies O, Baeten D. A single determination of C-reactive protein does not suffice to declare a patient with a diagnosis of axial spondyloarthritis ‘CRP-negative.Arthritis Res Ther. 2018;20(1):209.