139 PROMIS in VWD, IPFDs and RBDs 5 DISCUSSION In this study, we demonstrate that the selected PROMIS measures are valid and reliable instruments to measure health-related quality of life in adults with VWD. The PROMIS CATs were considered feasible, since the number of completed items of the selected set of CATs was only slightly higher than that of the SF-36v2. In addition, the CATs had less floor and ceiling effects than the SF-36v2. This implies that the PROMIS CATs more adequately cover the range of functioning of adults with VWD. The PROMIS fixed scale global health was also considered feasible, with a lower number of completed items and similar floor and ceiling effects compared to the SF-36v2. The PROMIS CAT anxiety and depression had a good construct validity, while all other PROMIS CATs had an excellent construct validity. All PROMIS measures are reliable for use on group-level. Moreover, all studied PROMIS CATs and the short form anger can be used to draw reliable conclusions on an individual patient level. Our study findings on the feasibility, construct validity and reliability of the PROMIS CATs are consistent with previous studies performed in Dutch patients with hemophilia 21,22. Regarding the relevance of the PROMIS CATs, our study findings are inconsistent with a previous study performed in Dutch patients with VWD. This previous study found that Dutch patients with VWD primarily experience a reduced vitality compared with the general population 12,30. Within this study, our population only reported slightly lower scores on the PROMIS CAT physical function compared to the Dutch general population 35,36,38. Our study population consisted primarily of patients with a non-severe beelding phenotype. This may explain the difference with the previous study, since patients with a severe bleeding disorder tend to have a more impacted healthrelated quality of life than patients with a non-severe bleeding disorder 12,30. In addition, our study population primarily consisted of females and elderly participants who both tend to score worse on physical functioning 15,57. Strengths and limitations This is the first study assessing the feasibility, measurement properties, and relevance of the PROMIS measures in patients with VWD. We followed the COSMIN guidelines, determined construct validity in a profound manner using the MTMM, and incorporated the latest methodology on reliability estimates 32,53,58. A possible limitation of this study is the limited information on the feasibility of the PROMIS measures compared to the SF-36v2. In our study, feasibility was determined based on the number of items needed to complete for the PROMIS
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