Diagnostic Value of Interleukin 6, Interleukin 12P70, Serum Amyloid A, and Procalcitonin for Rheumatoid Arthritis and Their Relationship With the Disease Activity

Objective To observe the diagnostic value of four serum inflammatory biomarkers, including interleukin 6 (IL-6), interleukin 12P70 (IL-12P70), serum amyloid A (SAA), and procalcitonin (PCT), in rheumatoid arthritis (RA) and to analyze their relationship with the disease activity.

Methods The study included 60 RA patients admitted to the Department of Rheumatology at Anhui Provincial Hospital of Traditional Chinese Medicine between December 2022 and December 2023. Thirty healthy individuals from the hospital’s physical examination center served as the control group. Serum levels of IL-6 and IL-12P70 were detected using flow cytometry. SAA levels were determined by immunoturbidimetry, and PCT levels were assessed by chemiluminescence. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), and anticyclic citrullinated peptide (ACCP) were detected using an automated biochemical analyzer. The 28-joint disease activity scores (DAS28-ESR) based on ESR were observed. Statistical analysis included t-tests, rank-sum tests, and Kruskal-Wallis H tests to compare the expression differences of the biomarkers among different groups. The diagnostic value of these biomarkers for RA was analyzed by ROC curve analysis. Spearman correlation analysis was performed to assess the relationships between the four inflammatory biomarkers and CRP, ESR, RF, ACCP, and DAS28-ESR.

Results 1) The expression levels of SAA, IL-6, and IL-12P70 in the RA group were significantly higher than those in the control group (P<0.01). 2) ROC curve analysis showed that the area under the curve (AUC) for PCT was 0.611 (95% confidence interval CI: 0.488-0.735, P>0.05), for SAA, it was 0.819 (95% CI: 0.733-0.906, P<0.01), for IL-6, it was 0.875 (95% CI: 0.803-0.946, P<0.01), and for IL-12P70, it was 0.832 (95% CI: 0.746-0.917, P<0.01). The combined index of IL-6, IL-12P70, SAA, and PCT had an AUC of 0.973 (95% CI: 0.942-1.000, P<0.01). This indicates that the four inflammatory biomarkers can assist in the diagnosis of rheumatoid arthritis. 3) The expression levels of PCT and SAA varied significantly among the high, moderate, and low activity RA groups (P<0.01). 4) In RA patients, CRP was positively correlated with SAA (r_s=0.75, P<0.01), and IL-6 (r_s=0.52, P<0.01). ESR was positively correlated with SAA (r_s=0.36, P<0.01). DAS28-ESR was positively correlated with PCT (r_s=0.34, P=0.01), SAA (r_s=0.51, P<0.01) and IL-6 (r_s=0.33, P=0.01).

Conclusion The four inflammatory biomarkers (PCT, SAA, IL-6, and IL-12P70) are closely related to rheumatoid arthritis disease activity and can serve as serum indicators to assist in the diagnosis and assessment of RA.