For a number of years, I have volunteered for the American Red Cross as a blood drive coordinator and staffer. It's an intensely rewarding experience. Here's a bit more about donating in the United States.

You must be at least 17 years of age and at least 110 pounds. You must also be in good health.

  • Accepted
    • Persons with asthma and allergies will be accepted if they are breathing normally and under control.
    • Someone taking blood pressure medication may still donate blood if they are within the limits on the day of donation.
    • Even cancer patients can give blood if it has been five years since their diagnosis, surgery, or last radiation treatment, as long as there has been no recurrence or chemotherapy.
    • If you have had dental work recently - teeth cleaning, root canal, a filling, or an extraction without an infection - you may still donate.
    • Diabetics can give blood if it has been two weeks since their initial dosage of insulin or a change in their dosage.
    • If someone with epilepsy has been seizure-free for three months - with or without medications - they are eligible to donate.
    • You cannot donate if you currently have mono, but if you are fully recovered donation is allowed.
    • Nursing mothers may donate.
    • If you have had surgery recently but the wound is healed and you have gone back to normal activity, you may donate blood.
  • Temporary Deferrals
    • If you have recently received a blood transfusion, you will be given a one-year deferral.
    • Oral surgery related to abscesses or infections requires a three-day deferral.
    • A two- to four-week deferral is given following vaccinations for rubella, chicken pox, oral polio, smallpox, or meningitis.
    • An individual will be deferred for three years after the last symptoms of malaria.
    • A pregnant woman will be deferred until six weeks after birth, unless a blood transfusion was required.
    • If you have had a tattoo or non-sterile body piercing, you will be deferred for a year and a day from the date you try to donate. Sterility is not a factor for the tattoo, but if the piercing was done by a certified piercer donation is permitted.
    • Those who have spent more than 72 consecutive hours in a correctional facility in the past year and individuals currently incarcerated will be deferred for twelve months, as will anyone who has been in a mental institution for more than 28 days.
  • Permanent Deferrals
    • Cancer patients with leukemia or lymphoma are not eligible to give blood.
    • Those with Creutzfeld-Jakob Disease will be indefinitely deferred, as will anyone with increased risk of CJD or with CJD-diagnosed relatives.
    • Anyone who has had hepatitis since the age of 11 will be permanently deferred.
    • A number of serious illnesses require permanent deferral, including lupus, Kaposi's sarcoma, Multiple Sclerosis, sickle-cell disease, and Lyme Disease.
  • AIDS and Blood Donation
    • If a health care worker has been exposed to the blood of someone with HIV, he or she must take a twelve-month deferral.
    • Permanent Deferrals
      • Men who have had sex with another man even once since 1977 are ineligible to give blood. This has caused some controversy among the gay community.
      • Anyone who has ever used a needle to inject illegal drugs or steroids will be permanently deferred.
      • Those who use clotting factor concentrates for a disorder such as hemophilia are not permitted to donate blood.
      • Anyone with AIDS or one of its symptoms, or anyone who has ever had a positive HIV test, may not give blood.
      • If you have had sex with an individual listed above within the past twelve months, you are not eligible to donate.
      • If, since 1977, you have received drugs or money for sex, you are not allowed to give blood.
      • Anyone born in one of a number of African countries since 1977 will be permanently deferred, as will anyone who has lived there for more than a year since 1977. Those who have received medical treatment with a blood product there are also ineligible. If you have had sex with anyone who was born in, has lived in, or received medical care in any of those countries since 1977, you are also deferred permanently from donation.

The Process
Every time you donate blood, you must fill out the same forms. When you are called, you will be given an interview behind a partition and your vitals (temperature, blood pressure, pulse) will be taken, as will a drop of blood to ensure you have enough red blood cells to donate safely. After you have passed the interview and drop test, you will be transferred to a table or reclining chair for the donation. It generally takes between ten and thirty minutes to donate a pint of blood, after which you will be escorted - even if you feel fine, someone will escort you - to an area with snacks and drinks to start the recovery process. Most donors feel fine within a couple of hours, but you shouldn't engage in any major activity for the rest of the day while the plasma is being replenished. It takes a couple of weeks to fully replace the cells taken during donation. Your blood is then tested for syphilis, HIV, and hepatitis and you will be notified if anything turns up positive. (The ARC emphasizes that one should not donate blood just to get an HIV test as their procedures are not perfect.)

Another important aspect of blood donation is platelet apheresis. Platelets, used to control bleeding, are needed by patients undergoing a bone marrow transplant, chemotherapy, an organ transplant, and surgery, but they have shelf life of just five days. Blood cell separators are used to withdraw the blood from the donor, recover the platelets, and then return the blood to the same donor. It takes longer than whole blood donation but is as vital, if not more so. Many donation centers have a TV for donors to watch or books and magazines to read during the two-hour process. Within 48 hours, the body has completely replaced all platelets, so you can donate every two days - but not more than 24 times annually.

...and personal experience.