Comparative analysis of rheumatoid factor levels by immune turbidimetry and latex agglutination assays among anti-cyclic citrullinated peptide-positive rheumatoid arthritis patients

Background: Rheumatoid arthritis (RA) is one of the most common contributors to the burden of chronic and debilitating polyarthritis. Materials and Methods: Over a period of 3 months, 264 symptomatic patients were tested for the presence of anti-cyclic citrullinated peptide (CCP) antibodies, and the first 50 patients with RA whose serum samples tested positive for anti-CCP (>10 AU/ml) were included in the study. Immune turbidimetric assay was employed to determine the titers of rheumatoid factor (RF) in patients of RA who have tested positive for anti-CCP and its performance was compared with latex agglutination testing modality. Results: Majority (82%) of the study population were female with a male-to-female ratio of 1:4.6. Latex agglutination test for RF using RHELAX-RF test kit yielded RF values ≥10 IU/ml in 31 (62%) patients, while the Immunoturbidimetric test: SPECTRUM RF Test Kit imparted RF titers ranging between 2.4 and 53.76 IU/ml, with a median RF titer of 22.22 IU/ml. The percentage agreement between the latex agglutination and immune turbidimetry assay for analyzing RF was 88%, with a strong positive correlation between latex agglutination and immune turbidimetry assay for RF (Spearman coefficient: r = 0.8097). Conclusion: Since the updated American College of Rheumatology/European League Against Rheumatism classification of RA underscores the precise titers of RF and anti-CCP in scoring RA, absolute titers of RF conferred by the immunoturbidimetry could be a welcome relief to slash inter-observer variations and hand out titers to better classify and treat patients of RA.