High-Sensitivity C-Reactive Protein as a Biomarker of Disease Activity in Psoriatic Arthritis

Objectives C-reactive protein (CRP) is commonly used to assess disease activity in psoriatic arthritis (PsA), yet fewer than 50% of patients with active PsA have elevated CRP levels. High-sensitivity C-reactive protein (hsCRP) assays detect lower concentrations missed by conventional methods but their role as biomarkers of PsA disease activity remains uncertain. We aimed to evaluate the association between hsCRP levels and clinical and sonographic measures of PsA activity. Methods We analyzed data from the Gladman-Krembil cohort that included patients with PsA followed from January 2016 to April 2025 (“clinical cohort”). Patients in this cohort are followed at 3-12-month intervals with standardized collection of medication use, PsA disease activity measures, patient-reported outcomes, and laboratory tests. The following measures of disease activity were assessed: Disease Activity measures included disease activity in Psoriatic Arthritis (DAPSA), clinical DAPSA (cDAPSA), Minimal Disease Activity (MDA), tender and swollen joint count (TJC, SJC), Psoriasis Area and Severity Index (PASI), enthesitis and dactylitis counts, patient pain, global assessment, and function, classifying patients as remission/low (DAPSA < 14) or moderate/high disease activity (≥14). HsCRP levels were measured using standardized high-sensitivity assays. A smaller subset underwent a comprehensive ultrasound of their joints/entheses before and 3 months following initiation of advanced therapy (“US cohort”). Total inflammatory sonographic scores, including synovitis, paratenonitis, tenosynovitis, and enthesitis, were calculated. Associations between hsCRP and clinical and sonographic measures of disease activity were analyzed using GEE multivariable regression models, which were adjusted for age, sex, and body mass index (BMI). Results A total of 1263 patients (10568 visits) from the clinical cohort and 144 patients (222 visits) from the US cohort were analyzed. Baseline mean hsCRP levels were 6.3±15.1mg/L and 8±12.4 mg/L in the clinical and US cohorts, respectively. Higher hsCRP was independently associated with higher DAPSA, TJC, SJC, dactylitis count, PASI (clinical cohort), and with patient-reported outcomes such as pain, global assessment of disease activity, and physical dyfunction (Table 1). Higher hsCRP levels were also significantly associated with reduced odds of achieving DAPSA-LDA, cDAPSA-LDA, and MDA. HsCRP was associated with SPARCC enthesitis score in the US cohort but not in the clinical cohort and with synovitis, paratenonitis, and tenosynovitis scores. HsCRP was associated with sonographic enthesitis count but not with the total enthesitis score. Table 1: The association between hsCRP and measures of PsA disease activity - GEE regression models Conclusion HsCRP is associated with both clinical and sonographic measures of inflammation in PsA. These findings support its utility as a simple, objective biomarker for monitoring both clinical and subclinical disease activity in PsA.