Implementing a primary-tertiary shared care model for enhancing cascade testing for familial hypercholesterolaemia: an effectiveness-implementation hybrid type III pre-post study.

Familial hypercholesterolaemia (FH) is a common but underdiagnosed genetic condition that leads to high low-density lipoprotein cholesterol and premature cardiovascular disease. Cascade genetic testing remains underutilised as a screening approach. Implementation strategies can increase the diffusion of innovations such as genetic medicine into non-genetic specialty settings more rapidly through dissemination networks. This study aimed to evaluate the success of a multifaceted implementation strategy to increase cascade testing for relatives of a person diagnosed with FH using a primary-tertiary shared care model. A multisite effectiveness-implementation hybrid type III pre-post study was conducted between 2022 and 2024 to compare the implementation of a new shared care model for FH cascade testing in NSW, Australia. During the control period, cascade testing of relatives was offered to FH index cases by a genetic counsellor at the lipid clinic. In the implementation strategy period, FH index cases were offered a cascade testing expression of interest form to provide to their relatives. Relatives were contacted by a genetic counsellor and provided with a pre- and post-cascade testing package, which was also provided to their general practitioner. A total of n = 25 index and n = 6 cascade cases were included in the control period and n = 81 index and n = 56 cascade cases in the implementation period. The number of cascade genetic tests per index case increased significantly from 0.24 in the control period to 0.52 in the implementation strategy period (incident rate ratio = 4.62; 95% CI: 0.39, 8.84; p = 0.032). Among relatives tested, there was no difference in the proportion with a confirmed FH gene change per index case (IRR = 2.15; 95% CI: 0.65, 7.01; p = 0.207). There was no difference in the proportion of index cases with at least one cascade test (OR = 1.49; 95% CI: 0.53, 4.19; p = 0.442). Implementation of our model increased FH cascade testing compared to previous standard care. These findings suggest a greater role for cascade testing in primary care settings. This opens new opportunities for integrating genetic screening into routine general practice, particularly for autosomal dominant conditions such as FH.