C-reactive protein thresholds for discriminating active disease in psoriatic arthritis may be different in early versus established disease.

Abstract

Objectives: Inflammatory biomarkers such as C-reactive protein (CRP) lack discriminatory capacity to detect active disease in psoriatic arthritis (PsA). Our aim was to find CRP thresholds capable of discriminating active disease in both early and established PsA.

Methods: We included a total of 345 PsA patients (215 early-onset not exposed to high-impact therapies and 130 with established disease under biologics and oral targeted therapies). Discriminative CRP thresholds were determined by the Youden index, while their sensitivity/specificity balance was evaluated by the area under the receiver-operating characteristic (AUROC) curve.

Results: Cohort I (recent-onset PsA) included 215 consecutive patients, mean age 49.8 ± 13.9 years, 145 men (67.4%) and 70 women (32.6%). Cohort II (established PsA: mean duration 9.2 ± 7.1 years) included 130 consecutive patients, mean age 55.6 ± 11.2 years, 64 men (49.2%) and 66 women (50.8%). In cohort II, a CRP value around 0.20 mg/dl resulted discriminative for active disease (AUROC 0.71, OR 4.7, p<0.001). Among patients not exposed to anti-TNF drugs in cohort II, a CRP ≥0.22 mg/dl was highly discriminative for active disease (AUROC 0.86). In cohort I, no CRP values ​​ with good discriminative performance were obtained in any scenario. The standard inflammatory CRP value (≥0.5 mg/dl) did not provide discriminative advantage above the previous thresholds in either cohort.

Conclusions: Our results suggest the adoption of lower than standard CRP cut-off values ​​ for a better assessment of PsA in clinical practice. This seems to be more applicable in established than in recent-onset PsA.