There are several reasons why you may be asked to defer your donation for another time. Some include: Blood pressure that is too high or too low, Low iron levels in the blood, Active cold or flu, Recently had major surgery, Are recovering from an infectious illness, Allergies, Diagnosed with Zika virus, West Nile, Ebola or SARS, Certain cancers, Certain heart conditions, Received a blood transfusion within the last year, Spending three months or more (cumulative) in the United Kingdom (England, Northern Ireland, Scotland, Wales, the Isle of Man, the Channel Islands, Gibraltar or the Falkland Islands) from 1980 through 1996, Spending five years or more (cumulative) since 1980 in Europe, Spending a total of 6 months or more associated with a military base between 1980 to 1996 in specific European countries, Certain medications, vaccines, growth hormones, transplants, grafts.