Blood donation
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.
Process
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.
Screening
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 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.
Donation
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, less than a pint, is drawn during the blood donation process.
Plasmapheresis
For the donation of plasma only, with the red cell component returned to the patient, the set-up for a donor is identical. The canula is then run to a means of collection:
- Blood (typically 600-700ml) is collected in a bag that is disconnected and spun in a centifuge to separate the red cells and plasma. The plasma (typically around 300ml) is drawn off. The bag is returned to the donor, reconnected to the canula, and the red cells run back to the vein.
- An automated centifuge machine takes an amount of blood and spins the red cells from the plasma. The red cells are periodically returned through the canula and the process repeated until the prescribed amount of plasma has been collected (typically 650ml).
- With this method, each plasma donation is optimised.
- This can be repeated at intervals of twice in seven days.
- The other obvious benefit of this method is that there is no potential confusion over what blood is returned to which donor, as may be possible with the first method.
In any case, it is important for the plasma donor to saturate their system with liquid in the 24 hours before donation, and particularly the day of the donation. This ensures that the blood plasma volume is maximised, and that the process runs smoothly.
Plasma is normally harvested for blood clotting 'factors' for use by people whose bodies do not produce these agents. Plasma donors can also be innoculated to allow particular antibodies to be harvested from their plasma.
Recovery
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, with red blood cell counts taking 4-5 weeks to recover.
Complications
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 blood, blood bank, blood transfusion, American Red Cross
