Minimal clinically important difference (MCID) in allergic rhinitis: Agency for Healthcare Research and Quality or anchor-based thresholds?
In 2013, the Agency for Healthcare Research and Quality (AHRQ) recommended that allergic rhinitis (AR) studies calculate a minimal clinically important difference (MCID) based on an estimated threshold equal to 30% of the maximum total nasal symptom score. Applying this threshold, their data showed no differences between well-established treatments, and a subsequent analysis using prescribing information found no differences between active treatments and placebo controls.
The objective of this study was to demonstrate the application of an evidence-based model to determine MCIDs for AR studies, with an absolute value for an anchor-based threshold and validated methods for calculating distribution-based thresholds.
Using the same studies as the AHRQ report, anchor- and distribution-based MCID thresholds were determined for 3 clinical comparisons identified by the AHRQ: (1) oral antihistamine+intranasal corticosteroid (INCS) versus INCS, (2) montelukast versus INCS, and (3) intranasal antihistamine+INCS in a single device versus the monotherapies. The outcomes were compared with those reported using the AHRQ threshold.
No treatment comparison met the AHRQ-defined MCID threshold; all treatments were determined to be equivalent for all 3 queries. In contrast, the evidence-based model revealed some differences between treatments: INCS > montelukast; intranasal antihistamine+INCS > either monotherapy. No clinically relevant benefit was observed for adding an oral antihistamine to INCS, but some studies were not optimal choices for quantitative determination of MCIDs. Updating the literature search revealed no additional studies that met the AHRQ inclusion criteria.
The evidence-based threshold for MCID determination for AR studies should supersede the threshold recommended in the AHRQ report.