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Isotype Measurement May Increase RA Diagnosis

Enhanced serologic testing could speed rheumatoid arthritis diagnosis and treatment

MONDAY, Aug. 16 (HealthDay News) -- The chance of serologically diagnosing rheumatoid arthritis (RA) could increase dramatically by measuring the presence of three rheumatoid factor (RF) isotypes, according to research published in the August issue of the Journal of Rheumatology.

Troy D. Jaskowski, of the Associated Regional and University Pathologists Institute for Clinical and Experimental Pathology in Salt Lake City, and colleagues analyzed serum samples from 1,021 general population patients (GPP) being tested because of a suspicion of RA, 137 with RA, 100 healthy blood donors, and 50 people with systemic lupus erythematosus, to examine the value of measuring RF isotypes in relation to IgG anti-cyclic citrullinated peptide (CCP) antibodies in the general population.

The researchers validated the positive predictive value and sensitivity of the anti-CCP2 test in the diagnosed group as 96 and 65 percent, respectively. The likelihood of a specimen from the GPP being positive for RF increased seven- and 21-fold with the identification of RF IgA and IgG in addition to IgM, respectively. Anti-CCP2 and anti-CCP3 agreement was significantly higher for RA+RF and GPP than for RF−RA, RF−GPP, and non-RA subjects. Healthy blood donors were significantly distinguished from the general population by presence of anti-CCP2, but not anti-CCP3.

"Measurement of the three isotypes of RF may increase by seven- to 21-fold the chance of making the serologic diagnosis of RA; a testing algorithm is proposed. The anti-CCP antibody response appears significantly less peptide-specific in the presence of IgM RF than in its absence," the authors write.

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