Central vs site outcome adjudication in the IRIS trial

Central adjudication of outcome events is the standard in clinical trial research. We examine the benefit of central adjudication in the Insulin Resistance Intervention after Stroke (IRIS) trial and show how the benefit is influenced by outcome definition and features of the adjudicated events.

IRIS tested pioglitazone for prevention of stroke and myocardial infarction in patients with a recent transient ischemic attack or ischemic stroke. We compared the hazard ratios for study outcomes classified by site and central adjudication. We repeated the analysis for an updated stroke definition.

The hazard ratios for the primary outcome were identical (0.76) and statistically significant regardless of adjudicator. The hazard ratios for stroke alone were nearly identical with site and central adjudication, but only reached significance with site adjudication (HR, 0.80; p = 0.049 vs. HR, 0.82; p = 0.09). Using the updated stroke definition, all hazard ratios were lower than with the original IRIS definition and statistically significant regardless of adjudication method. Agreement was higher when stroke type was certain, subtype was large vessel or cardioembolic, signs or symptoms lasted > 24 h, imaging showed a stroke, and when NIHSS was ≥3.

Central stroke adjudication caused the hazard ratio for a main secondary outcome in IRIS (stroke alone) to be higher and lose statistical significant compared with site review. The estimate of treatment effects were larger with the updated stroke definition. There may be benefit of central adjudication for events with specific features, such as shorter symptom duration or normal brain imaging.