The search for laboratory measures of outcome in rheumatoid arthritis.

A large number of laboratory tests have been developed within the past decade to measure factors involved in the immune inflammation of RA. These can be divided into genetic markers, general measures of inflammation, autoantibodies and tissue-specific markers. In general, it is simpler to prove the power of a certain test to measure the disease process than to predict outcome. Apart from RF positivity and CRP/ESR, few, if any, tests have proven to be of importance in independent studies from different centres. Among the promising candidates for future work are detailed analysis of the HLA-D region genes, sulphoxidation status, the autoantibody against RA33 nuclear antigen, soluble IL-2 receptor measuring lymphocyte activity, hyaluronate/hyaluronan or PIIINP from synovial tissue, the combined use of COMP and proteoglycan epitope tests for cartilage matrix, and pyrodinoline cross-linking for collagen from bone and cartilage. The ideal setting for testing such markers are prospective cohort studies starting early in the disease, and since many such studies have been initiated recently, one can expect much new information in coming years. Attention needs to be devoted to the kinetics of marker metabolism, since many are degraded or removed at very fast rates from the circulation, making serum assays less informative.