Sensitivity and specificity of autoantibodies binding to citrullinated carboxyterminal telopeptides of types I and II collagens in an early arthritis series.

OBJECTIVE To assess the specificity and sensitivity of autoantibodies binding to citrullinated carboxyterminal telopeptides of types I and II collagens in an early arthritis series. METHODS A cohort of 146 patients from the Kuopio 2000 Arthritis Survey having RA, AS, PsA, ReA, uSpA or undifferentiated arthritis were studied. Autoantibodies binding citrullinated types I and II carboxytelopeptides were measured in two different inhibition ELISA assays. Sera from 135 adult persons were used as controls. RESULTS In RA, the sensitivities were 0.83 with long type I telopeptide and 0.78 with long type II telopeptide and the respective specificities were 0.94 and 0.93, while the corresponding values in other inflammatory joint diseases were much lower. The likelihood ratio in RA increased with longer peptides from 4.20 to 14.06 for type I telopeptide and from 2.74 to 11.67 for type II telopeptide. CONCLUSION The antibody assay using long telopeptide from type I collagen was the most specific and sensitive method in every diagnostic category, although in the arthritides other than RA, binding was much less abundant and possibly citrulline-independent.