Anti-Citrullinated Albumin Antibodies As Biomarker For The Diagnosis Of Rheumatoid Arthritis

ObjectiveCitrullinated human serum albumin has been previously reported in serum and synovial fluid from individuals with rheumatoid arthritis (RA), and antibodies to citrullinated human serum albumin (ACA) have been identified in RA serum. We developed a point-of-care (POC) test for ACA and evaluated its sensitivity and specificity in healthy subjects and subjects with clinically diagnosed RA and other rheumatic conditions and autoimmune disease. MethodsThe POC test is a lateral-flow immunoassay using antihuman IgA/G/M and anti-human serum albumin antibodies for detection of citrullinated serum albumin-ACA complexes. This test was used to determine serum or plasma ACA levels in a South Asian study population comprised of healthy controls (n=484) and subjects with clinically diagnosed RA (n=354) or other rheumatic (n=103) and autoimmune diseases (n=60), and compared to the levels of rheumatoid factor (RF) and anticitrullinated cyclic peptide antibodies (ACPA). ResultsSensitivity of ACA for RA was 0.520 and specificity was 0.994. ACA prevalence in other rheumatoid disease was similar to that of ACPA and less than that of RF. ACA was detected in 12% of RA samples that were negative for ACPA. The combined sensitivity of ACA+ACPA was 0.664 and the combined specificity was 0.845. ConclusionThe ACA POC test exhibits robust sensitivity and specificity for RA diagnosis in serum or plasma and, in conjunction with ACPA, can enable rapid and efficient differential diagnosis of RA with increased sensitivity and comparable specificity.