The Self-Administered Rheumatoid Arthritis Disease Activity Index (RADAI) is Less Accurate than DAS28-CRP as a Disease Activity Measure in Pregnancy

Abstract

Objective: Disease Activity Score 28 (DAS28)–using the C-reactive protein (CRP) level has been validated to determine disease activity in rheumatoid arthritis (RA) patients during pregnancy. A self-administered questionnaire like Rheumatoid Arthritis Disease Activity Index (RADAI) has practical advantages over DAS28-CRP, and in this study, we aimed to validate the RADAI for use during pregnancy. Methods: Patients were derived from a prospective cohort on RA and pregnancy (Pregnancy-induced Amelioration of Rheumatoid Arthritis study). To validate the RADAI as a disease activity measure, the disease course over time and the disease activity states were compared with the DAS28-CRP. Furthermore, the RADAI was compared with DAS28-CRP in predicting fertility and pregnancy outcomes. Finally, to test construct validity, correlation of both RADAI and DAS28-CRP with a biomarker (galactosylation of immunoglobulin G [IgG]) were determined and compared. Results: In total, 269 patients were analyzed in this study. Mean RADAI scores showed a great decline in disease activity in the first trimester compared with DAS28-CRP (mean RADAI, −1.13; mean, DAS28-CRP, −0.04). Correlations between DAS28-CRP and RADAI scores were moderate to good (0.44 < ρ < 0.71). Agreement in disease states was low (0.26 < κ < 0.51). Time to pregnancy was different between disease states according to DAS28-CRP (P = 0.03), but not according to RADAI (P = 0.56). Only DAS28-CRP could predict birthweight (DAS28-CRP β-0.17, P = 0.04; RADAI β-0.09, P = 0.10). Both DAS28-CRP and RADAI were associated with galactosylation of IgG at specific time points, but only change in DAS28-CRP was correlated with change in galactosylation of IgG from preconception to pregnancy. Conclusion: The RADAI could not be validated as a disease activity measure during pregnancy. DAS28-CRP remains the gold standard of measuring disease activity in pregnancy.