IgA rheumatoid factor in rheumatoid arthritis.

Area of Science:

• Rheumatology
• Immunology
• Clinical Diagnostics

Background:

• Rheumatoid factor (RF) is crucial for rheumatoid arthritis (RA) diagnosis.
• Current research primarily focuses on IgM RF and total RF assays.
• The diagnostic utility of IgA RF in RA requires further investigation.

Purpose of the Study:

• To evaluate the added diagnostic value of IgA RF in rheumatoid arthritis.
• To compare the performance of IgA RF assays with established RA biomarkers.
• To assess the impact of incorporating IgA RF into existing RA classification criteria.

Main Methods:

• An international cohort of 398 RA patients and 1073 controls was tested for IgA RF using three commercial assays.
• Clinical and serological data for ACR/EULAR classification were collected.
• IgA RF sensitivity and specificity were compared to IgM RF and anti-citrullinated protein antibodies (ACPA).

Main Results:

• IgA RF demonstrated lower sensitivity for RA diagnosis compared to IgM RF.
• IgA RF levels were highest in patients with primary Sjögren's syndrome.
• Double positivity (IgM RF and IgA RF) increased RA specificity but reduced sensitivity.
• Combined positivity (IgA RF, IgM RF, and ACPA) enhanced specificity while decreasing sensitivity for RA classification.

Conclusions:

• IgA RF alone exhibits lower sensitivity than IgM RF for RA diagnosis.
• Incorporating IgA RF into RA classification alongside IgM RF and ACPA does not improve sensitivity.
• Combined IgA RF, IgM RF, and ACPA positivity significantly increases the specificity of RA classification.