Serum amino-terminal type III procollagen peptide in rheumatoid arthritis. Relationship to disease activity, treatment, and development of joint erosions.

Using 2 radioimmunoassays, increased serum levels of amino-terminal type III procollagen peptide and its degradation products were demonstrated in rheumatoid arthritis patients. Patients with active disease showed higher serum propeptide levels than did patients with inactive disease. Unlike D-penicillamine, azathioprine treatment suppressed the propeptide levels in patients with active disease. A 6-month prospective study showed significantly higher initial serum propeptide levels in patients with erosive progression. The propeptide level reflects disease activity and may be a valuable prognostic marker in rheumatoid arthritis.