Establishing the minimum clinically important difference for the Genetic Counseling Outcome Scale (GCOS-24).

To establish the smallest change in genetic counseling outcome that is meaningful for patients, the aim of this study was to establish the Minimum Clinically Important Difference (MCID) for the Genetic Counseling Outcome Scale (GCOS-24). GCOS-24 is a patient-reported outcome measure for clinical genetics services. Secondary aims included understanding what patients deem important for reaching this score. Participants were 74 new patients recruited from the All Wales Medical Genetics Service, between April 2016 and December 2016. An anchor-based, global transition question methodology was used to identify the MCID, by asking participants how much meaningful change they experienced following their genetics appointment, and comparing this with GCOS-24 change scores. This ensured that the established score was clinically meaningful to patients. Comments from a free text response box were analyzed using qualitative thematic analysis. The mean score of the group who felt "a little better" was determined to be the MCID. The MCID was established to be a GCOS-24 score increase of 10.3 points after a clinical genetics appointment. This score was significantly different from the group "neutral" (0.64 points), using an independent samples t test. Themes identified as important for reaching the MCID included "future and family". These findings contribute to interpretability of GCOS-24 and provide some useful insights for genetic counseling service development.