BACKGROUND: Roughly one quarter of short-term temporary deferrals (STTDs) of blood donors are low hemoglobin deferrals (LHDs), i.e. STTDs due to a hemoglobin (Hb) value falling below a cutoff of 125g/L for female and 135g/L for male donors. Since voluntarily donating blood is a prosocial activity, donors may perceive deferrals as social exclusion, which can cause social pain, decrease self-esteem, and lead to anti-social behavior. Yet, little is known about the causal impacts of LHDs on donor return.
STUDY DESIGN AND METHODS: We use a quasi-experiment with 80,060 donors, invited to blood drives in the canton of Zurich, Switzerland between 2009 and 2014. Within a narrow window of Hb values around the predetermined cutoff, the rate of LHDs jumps discontinuously. This discontinuous jump allows us to quantify the causal effect of LHDs on donor return, as it is uncorrelated with other unobserved factors that may affect donor return too.
RESULTS: We find different behavioral reactions to LHDs for female and male donors. Female donors do not react to the first LHD. However, after any repeated LHD, they are 13.53 percentage points (p-value < 0.001) less likely to make at least one donation attempt within the next 18 months and make 0.389 fewer donation attempts (p-value < 0.001). Male donors already react to the first LHD. They are 5.32 percentage points (p-value: 0.139) less likely to make at least one donation attempt over the next 18 months and make 0.227 (p-value: 0.018) fewer donation attempts. After any repeated LHD, male donors are 13.30 percentage points (p-value: 0.004) less likely to make at least one donation attempt and make 0.152 (p-value: 0.308) fewer donation attempts.
CONCLUSION: LHDs have detrimental impacts on donor return, especially if they occur repeatedly – suggesting that avoiding false LHDs and helping donors to better cope with them helps to maintain the pool of prospective donors.