blood donations

The INTERVAL trial in the United Kingdom investigated the optimal frequency of blood donations and its effect on the donor’s health.

Blood donations have saved countless lives by enabling blood transfusions for several clinical indications. However, there have been no studies investigating strategies to obtain the most blood with minimal adverse effects on donors. Consequently, there are drastic differences in blood collection policies and practices between different countries. For instance, in the United Kingdom, men and women can donate blood every 12 and 16 weeks, respectively. In contrast, in the United States, men and women can both donate blood every eight weeks. Furthermore, observational studies suggest that shorter durations may increase the frequencies of iron deficiency, lower haemoglobin concentrations, and increase rates of deferrals (refusal to take blood from a donor).

A recent trial in the United Kingdom called the INTERVAL trial, published in The Lancet, investigated the effects of blood donation frequency on blood supply and donor health over a two-year period. Participants over the age of eighteen and fulfilling criteria for blood donation were recruited to the study. There were 22,466 men and 22,797 women who participated in this first-ever randomized trial concerning blood donations.  The men were randomly assigned to 12, 10, or 8-week inter-donation intervals, whereas the women were randomly assigned to 16, 14, or 12-week inter-donation intervals. After 6, 12, 18, and 24 months, donors were required to complete a questionnaire assessing their safety characteristics. Furthermore, at the two-year mark, participants also completed cognitive and physical tests. The trial aimed to determine the number of blood donations over the two-year period and assess donor safety profiles, including quality of life, donation-related symptoms, physical activity, cognitive function, haemoglobin and ferritin concentrations, and deferral frequency.

Researchers compared measurements to the standard donation frequency in the United Kingdom, which is 12 weeks for men and 16 weeks for women. Compared to the standard inter-donation interval, the mean amount of blood collected per male donor, increased by 1.69 and 0.79 units in the 8 and 10-week interval group, respectively. Similarly, in women, the mean amount of blood collected per donor relative to the standard increased by 0.84 and 0.46 units in the 12 and 14-week interval group, respectively. No differences between physical activity, cognitive function, and the incidence of major adverse effects were found between the randomized groups. Interestingly, however, self-reported symptoms including feeling faint, tiredness, breathlessness, and dizziness were moderately higher in the more frequently donating groups. The authors also found that haemoglobin and ferritin concentrations (markers of iron deficiency) were lower in participants assigned to the shorter interval groups, which likely contributed to their higher frequency of deferrals.

The INTERVAL study demonstrated that the amount of blood donations can be significantly increased by reducing the duration between donations, without affecting the donor’s physical activity, cognitive function, and quality of life. However, more frequent donations were associated with a reduced iron count in the form of haemoglobin and ferritin. Consequently, a higher proportion of donors were deferred, which can be time-consuming and costly for blood services and demotivate donors. The authors propose that individuals with higher than average initial haemoglobin and ferritin concentrations could be ideal candidates for more frequent donations. In other words, the current study highlights the possibility of personalized donation strategies to collect more blood without negatively affecting donor health.

Written by Haisam Shah, BSc


Di Angelantonio, E., Thompson, S. G., Kaptoge, S., Moore, C., Walker, M., Armitage, J., … & INTERVAL Trial Group. (2017). Efficiency and safety of varying the frequency of whole blood donation (INTERVAL): a randomised trial of 45 000 donors. The Lancet.

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