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TORONTO — Unlike standard C-reactive protein (CRP) testing, results from high-sensitivity CRP (hs-CRP) testing may be a reliable marker of psoriatic arthritis (PsA) disease activity, findings from a large new study suggested. 

“We found that higher sensitivity CRP was independently associated with composite, individual, and sonographic measures of disease activity,” study author Ujjwol Prasad Risal, MD, told Medscape Medical News.

The hs-CRP test also identified patients who were less likely to achieve low disease activity (LDA) and minimal disease activity (MDA) states, said Risal, who until recently was a clinical research fellow in PsA at Women’s College Hospital and the Department of Medicine at the University of Toronto, Toronto, Ontario, Canada. He is currently a rheumatologist and assistant professor at the B.P. Koirala Institute of Health Sciences, Dharan, Nepal.

The results were presented as a poster during the Spondyloarthritis Research and Treatment Network (SPARTAN) 2026 Annual Meeting.

Conventional CRP testing may be useful for other types of arthritis, such as rheumatoid arthritis, but it has limited accuracy in detecting active PsA, particularly at lower levels of inflammation — for example, at values < 10 mg/L, Risal said.

“Even in patients with active inflammation, CRP is raised only in around 50% of patients, which means 50% of patients with active disease may have normal CRP,” he said.

Hs-CRP testing, which is useful in predicting cardiovascular disease and is being used in other areas of medicine, utilizes a more sensitive assay to detect CRP in the blood to improve identification of “even minimal inflammation or low-grade inflammation,” Risal said.

Hs-CRP’s Links to Disease Activity With and Without Ultrasound Data

Hs-CRP’s utility as a biomarker of PsA disease activity has not been clear, however, leading Risal and colleagues to conduct a prospective cohort study of 1060 adult patients with PsA who fulfilled classification criteria for PsA. They were a mean age of 51.5 years (45.9% female), with a mean baseline Disease Activity in PsA (DAPSA) score of 14.4. (A DAPSA score < 14 indicates LDA and > 14 indicates moderate disease activity.) The researchers followed study participants at 3- to 12-month intervals, and they measured hs-CRP using a commercial assay.

A subset of 144 patients also underwent standard musculoskeletal ultrasound prior to, and 3 months after, initiating advanced therapy for active PsA to assess inflammation in their joints, entheses, and tendons. These patients had a mean age of 48.2 years, a mean DAPSA of 23.5, and 54.2% were women.

In a multivariable regression analysis to determine the association between hs-CRP and measures of PsA disease activity (per 10-unit increase in hs-CRP), Risal and colleagues found that higher hs-CRP was independently associated with DAPSA score in the clinical cohort (adjusted beta-coefficient, 2.37; 95% CI, 1.87-2.87; P < .001) and in the ultrasound cohort (adjusted beta-coefficient, 7.67; 95% CI, 4.31-11.03; P < .001), as well as other composite measures of disease activity, and patient-reported outcomes (including pain) and PsA-specific musculoskeletal domains.

The Spondyloarthritis Research Consortium of Canada enthesitis count was associated with hs-CRP in the ultrasound cohort (risk ratio, 1.20; 95% CI, 1.07-1.36; P = .002) but not in the clinical cohort.

Higher hs-CRP was independently associated with higher sonographic disease activity based on total synovitis score (adjusted beta-coefficient, 11.06; 95% CI, 4.02-18.09; P = .002) and paratenonitis score (adjusted beta-coefficient, 3.25; 95% CI, 1.80-4.71; P < .001) but not tenosynovitis score, whereas the total counts of joints with synovitis, paratenonitis, enthesitis, or tenosynovitis were each significantly and independently associated with higher hs-CRP.

And for disease activity states, higher hs-CRP was associated with reduced odds of achieving MDA, DAPSA-LDA, and clinical DAPSA-LDA.

Hs-CRP had moderate discriminatory ability for identifying LDA states. The researchers obtained an area under the curve (AUC) of 0.63 for DAPSA-LDA using a “cutoff” hs-CRP value of 3.60 mg/L.

“That m eans that if the CRP is higher than 3.60, patients are at lower likelihood of getting or achieving the DAPSA – LDA state,” Risal said.

Similarly, the AUC was 0.62 for MDA using a cutoff of 3.45 mg/L.

Clinical Implications

Risal said that these results should be useful for rheumatologists in treating patients with PsA. “Even though the discriminatory performance of hs – C R P was moderate, the study provides additional objective information for use in routine monitoring of patients.”

But when asked to comment on the study for Medscape Medical News, Matthew Stoll, MD, PhD, professor of pediatrics in the Division of Pediatric Rheumatology at The University of Alabama at Birmingham and Children’s of Alabama in Birmingham, Alabama, said the findings may not have a huge impact as the management of PsA “is driven by the full clinical picture,” and isn’t based solely on CRP levels.

“For example, if a patient has active arthritis and/or psoriasis, I’m going to recommend altering their systemic immunomodulatory therapy, regardless of the CRP test result.”

And for a patient who appears to be clinically doing well but has a high CRP, he may look more closely for inflammation. “I may image a previously active joint or perhaps bring that patient back in a bit sooner than I would have otherwise, but I wouldn’t alter their management on the basis of the lab test alone,” he said.

Like other pediatric rheumatologists, Stoll uses CRP along with other inflammatory markers to monitor disease activity and progression in patients with PsA. But like most in the field, he’s limited to the version of the CRP test used by the laboratory where he’s affiliated (Children’s of Alabama), which uses standard CRP testing.

But if clinicians do have access to hs-CRP testing, the optimal hs-CRP cutoffs identified in the study for DAPSA-LDA and MDA make hs-CRP measurements “a practical, objective tool to flag patients unlikely to achieve low disease activity in routine clinical practice,” Abhijeet Danve, MD, associate professor of medicine (rheumatology, allergy, and immunology) and director of the Spondyloarthritis Program at Yale University School of Medicine, New Haven, Connecticut, told Medscape Medical News. He was not involved in the study.

No outside funding source for the study was identified, and the researchers did not report having any relevant financial relationships with industry.