Estimation of the Harvey Bradshaw Index from the Patient-Reported Outcome 2 in Crohn's Disease: Results Based on a Large Scale Randomized Controlled Trial.

BACKGROUND

Many registrational trials in Crohn's disease assess treatment efficacy with the 2-item Patient-Reported Outcome (PRO2), while the Harvey-Bradshaw Index (HBI) is prominent in pragmatic trials and clinical practice. The translation between PRO2 and HBI has not been established.

METHODS

Data from a Phase 3 trial of vedolizumab in Crohn's disease were used to determine the Pearson correlation between PRO2 and HBI. Linear regression was used to fit equations that estimate between indices; 95% prediction intervals were determined for HBI scores corresponding to PRO2 thresholds for disease activity. Internal validation of the conversion equations was performed using the bootstrap methods.

RESULTS

PRO2 and HBI were highly correlated at baseline (r = 0.75 95% confidence interval (CI) 0.73-0.78; P < .001), induction (r = 0.87; 95% CI, 0.85-0.88; P < .001), and maintenance (r = 0.88; 95% CI, 0.85-0.90; P < .001). PRO2 and HBI change scores were moderately correlated (r = 0.72; 95% CI 0.69-0.75; P < .001) in induction and more strongly correlated during maintenance (r = 0.81; 95% CI 0.78- 0.84; P < .001). Regression equations for conversion of PRO2 to HBI from all cohorts (induction, maintenance, randomized, open-label) support an approximate conversion where HBI = 0.5 PRO2. As expected from the imperfect correlation between scores, the prediction intervals were generally wide. No evidence of overfitting was seen in bootstrap internal validation.

CONCLUSIONS

PRO2 and HBI correlate strongly and conversion between them is possible. These findings facilitate the practical application of trial results and clinical guidelines.