Development and Validation of a New Disease Activity Index as a Numerical Sum of Four Variables in Patients With Early Arthritis

Abstract

To describe the development and validation of a disease activity index in early arthritis that can be easily applied in daily practice and clinical research. The Hospital Universitario La Princesa Index (HUPI) was developed after analysis of data from an early arthritis cohort (202 patients with 756 visits). It is the sum of 4 variables (graded 0-3): tender joint count, swollen joint count, patient global assessment, and acute-phase reactants (erythrocyte sedimentation rate [ESR] and/or C-reactive protein [CRP] level, depending on availability at the moment of evaluation). The score for each variable was based on its quartile distribution in the cohort. The HUPI was validated using the following properties: feasibility, internal consistency (Cronbach's alpha), convergent validity (Pearson's r coefficients with other activity measures), criterion validity (area under the receiver operating characteristic curve [AUC ROC] to detect minimal disease activity [MDA]), and sensitivity to change (AUC ROC) to detect change with the physician's and patient's assessment of disease activity. Internal consistency is reasonable (α = 0.63). The HUPI correlates well with activity measures such as the Disease Activity Score in 28 joints (DAS28; r = 0.89) and the Simplified Disease Activity Index (SDAI; r = 0.70), and correlates slightly worse with the functional index of the Health Assessment Questionnaire (r = 0.69). It discriminates MDA correctly (AUC 0.95), and its sensitivity to change is slightly superior (AUC 0.902) to that of the DAS28-ESR (AUC 0.864), the DAS28-CRP (AUC 0.889), and the SDAI (AUC 0.791). The HUPI has face validity, is easy to calculate, is sensitive, and is a valid composite index for the assessment of disease activity in patients with early arthritis, both in clinical research and in routine care.