Purpose: Reliable measures are required for proper cost-utility analysis after critical care. No gold standard is available, but the EQ-5D health-related quality of life instrument (HRQoL) has been proposed. Our aim was to compare the EQ-5D with another utility measure, the 15D, after critical illness.
Methods: A total of 929 patients filled in both the EQ-5D and 15D HRQoL instruments 6 and 12 months after treatment at an intensive care or high-dependency unit. The difference in the medians and distributions of the scores of the instruments was tested with Wilcoxon signed-rank test and their association with Spearman rank correlation. Discriminatory power was compared by the ceiling effect and agreement between the instruments regarding the direction of the minimal clinically important change in the HRQoL scores between 6 and 12 months was tested with the McNemar-Bowker test and Cohen's kappa.
Results: The utility scores produced by the instruments and their distributions were different. Agreement between the instruments was only moderate. The 15D appeared more sensitive than the EQ-5D both in terms of discriminatory power and responsiveness to clinically important change.
Conclusion: The agreement between the two utility measures was only moderate. The choice of the instrument may have a substantial effect on cost-utility results. Our results suggest that the 15D performs well after critical illness, but further large cohort studies comparing different utility instruments in this patient population are warranted before the gold standard for utility measurement can be announced.