Abstract
IntroductionThe aim of this study was to examine seroconversion and the relationship with age and inflammation of autoantibodies in a large group of patients attending an outpatient rheumatology clinic.MethodsLevels of antibodies to citrullinated proteins/peptides (ACPAs) and IgM rheumatoid factor (IgM-RF) were determined in 22,427 samples collected from 18,658 patients. The diagnosis was derived from a diagnosis registration system. The degree of seroconversion in repeated samples and the correlation of levels with age and inflammatory markers were determined for ACPA and IgM-RF in rheumatoid arthritis (RA) and non-RA patients.ResultsSeventy-one percent of RA patients (n = 1,524) were ACPA-positive and 53% were IgM-RF-positive; in non-RA patients (n = 2,245), the corresponding values were 2% and 4%, respectively. In patients with at least two samples (n = 3,769), ACPA status was more stable than IgM-RF status in RA patients. ACPA- or IgM-RF-negative non-RA patients seldom became positive. ACPA positivity was unrelated to age in both RA and non-RA patients. IgM-RF positivity was unrelated to age in RA patients; however, it increased with age in non-RA patients. The correlation between autoantibody levels and inflammatory markers was low in general and was somewhat higher for IgM-RF than for ACPA.ConclusionsACPA status is more stable in time and with increasing age than IgM-RF status, further establishing its role as a disease-specific marker. ACPA and IgM-RF levels are only moderately correlated with markers of inflammation.
Highlights
The aim of this study was to examine seroconversion and the relationship with age and inflammation of autoantibodies in a large group of patients attending an outpatient rheumatology clinic
In patients with at least two samples (n = 3,769), ACPA status was more stable than IgM rheumatoid factor (IgM-RF) status in rheumatoid arthritis (RA) patients
IgM-RF positivity was unrelated to age in RA patients; it increased with age in non-RA patients
Summary
The aim of this study was to examine seroconversion and the relationship with age and inflammation of autoantibodies in a large group of patients attending an outpatient rheumatology clinic. One of the frequent characteristics of rheumatoid arthritis (RA) is the presence of antibodies to citrullinated proteins/peptides (ACPAs) and/or IgM rheumatoid factor (IgM-RF) [1]. ACPAs target citrullinated proteins and are observed in around 70% of RA patients. In contrast to IgM-RF, ACPA is highly specific for RA (specificity 80% versus 96%, respectively) [3]. Besides their well-established superior specificity for RA, several other properties of ACPA are distinct from IgM-RF. About 50% to 70% of early-RA patients are ACPA-positive, and this phenotype remains fairly stable thereafter [2,5,6], even during treatment with tumour necrosis factor (TNF)-blocking agents [7]. IgM-RF levels decrease during antirheumatic treatment [8] and 17% of IgM-RF-positive RA patients turned negative after 6 months of anti-TNF treatment [9]
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