I got this information from the San Pedro Sun:
There is a big blood drive on Ambergris Caye soon - September 4th from 9am. The location is next to El Torito and Island Adventures - right in town. Blood can only be stored for a short period of time which is why the hospitals need a constant supply of fresh donations. A healthy adult can donate a pint quite easily and the body makes more over a short period of time.
Donors must be between the ages of 18 - 65 years.
You must eat an adequate size meal prior to making the donation.
Your last donation must have been at least 3 months prior to donating.
Your latest tatoos must be at least a year old.
Menstruation must have stopped at least a week prior to donating.
It must have been a year since your last major surgery, transfusion of blood, pregnancy or miscarriage.
You must wait 2 years after your last malaria infection.
You cannot donate blood if you have HIV, AIDS, if you have had hepatitis over the age of 11 years, asthma, hypertension, diabetes, heart disease or if you are presently ill.