Sarah P. Coundouris

Diversification of blood collection agencies' (BCAs) core business requires donors to donate substances of human origin (SoHO) beyond whole‐blood. Whole‐blood donors are assumed to be willing to convert to donate other SoHO as well as whole‐blood. However, no reviews consider the evidence on conversion (i.e., willingness/intention, behaviour, retention, attrition). This rapid review provides a narrative synthesis of whole‐blood donors' conversion to another SoHO, characteristics contributing to conversion, motives and deterrents, and interventions encouraging conversion. Sixty‐five studies were reviewed. Most were cross‐sectional and examined whole‐blood donor conversion to organ (willingness/pledge for deceased donation), plasma or stem cell donation. Most examined conversion rather than characteristics contributing to conversion, motives, deterrents or interventions. Whole‐blood donors appear willing to donate another SoHO, yet conversion rates are unclear. Besides self‐efficacy, there is little consistency in reported characteristics of donors converting, and few theories applied to understand characteristics encouraging conversion. Intrinsic (altruism, self‐esteem, curiosity) and extrinsic (perceived need, service experience, direct requests) motives and barriers (lifestyle, fearing reduced health) appear important and require further research. Interventions encouraging conversion need replication and may include in‐person, in‐centre approaches, raising awareness of the functional benefits of other SoHO (high need, usefulness), and developing promotional materials that pique donors' curiosity, invite questions, and encourage donor‐initiated conversations about conversion. Centralising BCAs as a single business or partnering with other organisations appears mutually beneficial to encourage conversion and sustainable panels/resources. Research is needed to understand the impact of encouraging conversion on donors and organisations, and identify optimal management strategies for multi‐SoHO donors.