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Article History

Received: 20 August 2019

Accepted: 26 March 2020

First Online: 10 April 2020

Ethics approval and consent to participate

: All procedures were reviewed and approved by Institutional Review Board of the Guangzhou Blood Center (Approval Number: GZBC20161001). Oral informed consents were only retrieved from donors in telephone group but not in other two groups, since it was a low-risk study comparing operational recruitment techniques that would have been applied to the donors in any case, except for randomisation; besides all data were processed anonymously. The ethics committee (The Institutional Review Board of the Guangzhou Blood Center) approved of the verbal consent procedure for participants in telephone group, and waiving the need for consent for the other two groups. All donors were not informed of the study goals or provided explanations about the nature of the interventions, otherwise they might have changed their return behaviour and thus compromised the results of the study. The Institutional Review Board of the Guangzhou Blood Center also approved these. The registration ID for this study on ClinicalTrial.gov is: NCT03366441.

: Not applicable.

: The authors declare that they have no competing interests.