Background: Retention of first-time donors is pivotal for blood collection centers. The present study built on research showing the importance of donor identity among regular donors and sought to compare the effectiveness of various communication strategies on return rate.

Study design and methods: Postal letters were sent to a large sample of first-time whole blood donors (N = 1219) a few weeks following their first donation. Four versions of this letter were differently constructed in a way to boost the acquisition of donor identity (i.e., by including information about their ABO and Rh(D) blood group, emphasizing the salience of donor identity, offering a keyring with personalized information, or specifying the percentage of those sharing the same ABO and Rh(D) blood group). One version with no identity-related information served as a control condition. Participants' subsequent blood donations were tracked for 5-22 months after receiving the letter.

Results: Survival analysis showed that the return rate was significantly higher among those who had received information about the percentage of the country's population with the same ABO and Rh(D) blood group (in comparison with the four other versions). There was no significant effect on the blood type rarity.

Conclusion: Blood collection centers could orient the strategy employed to communicate with first-time donors to improve donors' retention. Arousing a sense of social identification with others with the same blood type may reveal a promising avenue.