Blood donation is a process by which a blood donor voluntarily has blood drawn for storage in a blood bank for subsequent use in a blood transfusion.
To understand the importance of the availability of a sustainable donated blood supply, the catch-cry of the Australian Red Cross Blood Service is, "80% of Australians will need blood in their lifetime, but less than 3% of Australians give blood each year."
Blood donations may be scheduled at local centers, or at times a "blood drive" will occur. These are events where a blood bank or other blood collecting organization will set up in a convenient location for people to stop in without appointment during their daily routine to donate blood.
The process of giving blood involves screening the donor, the actual donation, and a brief recovery period.
This applies to both whole blood donations and plasmapheresis (giving of plasma only) - see Donation below.
Western countries typically impose screening for blood donor candidates. When a donor arrives at a donation site, the donor typically fills out a consent form as well as answering a brief survey to help determine their eligibility. Questions include the donors's age, weight, most recent donation, current health, and various risk factors such as tattooing, drug use (recreational or performance enhancing), recent international travel, and sexual history. Answers are associated with your blood, but not your name to provide anonymity.
Often the blood hemoglobin concentration will be checked next, typically performed by a phlebotomist. While various tests exist, the most common ones are:
- hematocrit: done in some places. requires a centrifuge. A measurement of >38% allows donation to continue.
- colorimetric hemoglobin test using a hemoglobin photometer : a machine-read result from a chemical reaction on a testing strip.
- copper sulfate screening test (aka "float test"): measures the specific gravity of the donor's blood by placing a drop into a copper sulfate solution. The solution is calibrated so that a hemoglobin concentration of in >12.5 g/dl (the cut-off in the U.S. for donation) sinks.
Additionally, the donor may indicate to not use their blood but still go through the blood drawing process, again to protect the individual's confidentiality. All blood is later tested for diseases including STDs. If a disease is found, the donor will be notified and their blood discarded. It is discouraged for individuals to use blood donation as anonymous STD screening.
The blood donation itself happens next. The donor lies prone on a cushioned bench and extends an arm. The inner elbow is disinfected, and a cannula is inserted into a vein. The donor often has a tourniquet wrapped around his or her arm, or may be prompted to squeeze a ball repeatedly, to help speed the process. Blood flows from the vein, through the needle and a tube, and into a special collection bag which is placed on a small scale to measure the amount of blood withdrawn. Typically, around 500 millilitres, about a pint, is drawn during the blood donation process.
Rather than donating whole blood, a donor sometimes has the option to donate only some blood components while retaining others. This process is known as apheresis, and is more involved, time consuming, and requires more specialized equipment. The benefit is that more of the desired components can be concentrated and removed, and the donor is usually able to donate significantly more frequently than if whole blood had been removed. In some cases, the usefulness of the removed components is not as sensitive to blood type considerations.
The typical method of apheresis is to draw whole blood from the donor, then centrifuge the blood to separate its components (see apheresis for more information). The desired components (e.g. platelets, plasma) are removed and then the remaining components are returned to the donor.
Once the donation is complete, the donor is given a bandage or gauze to stop further blood flow and is normally allowed to leave. Beverages are often provided to donors to help them restore blood volume, and snacks may also be available. In some countries, stickers are sometimes worn by donors for the duration of the day, showing the donor's pride and encouraging others to donate as well. The entire process is usually completed in 15 to 30 minutes. The donor is discouraged from heavy exercise or lifting until the next day. Plasma volumes will return to normal in around 24 hours, while red blood cells are replaced by bone marrow into the circulatory system within about 3-5 weeks, and lost iron replaced over 6-8 weeks.
Finger prick and needle insertion typically cause only minor discomfort, but with some donors, phlebotomists may experience difficulties obtaining enough blood.
During the donation, hypovolemia may occasionally lead to a drop in blood pressure with some donors experiencing light-headedness. In some cases this may necessitate cancelling the donation, restoring blood volume with an intravenous infusion, or placing the donor in a Trendelenburg position (on a stretcher tilted "legs up"). Beverages may be given to further replenish blood volume, and the donor may have to remain in a prone position for a while under monitoring.
In a small number of cases, canulization can be followed by bruising in the weeks afterwards. This is rarely serious enough to require additional medical attention; if you experience bruising, consult your blood center or doctor.
Negative medical reactions to blood donation are rare and blood bank staff are well trained to handle them.
See also: blood, blood bank, blood transfusion, American Red Cross