Second of 2 posts from student questions this coming week. Got a question to “Ask Prof”? Send an email, so I’ll remember! And I’ll put it in the queue 🙂
So we finished neuro and started cardiovascular. Students asked all sort of blood questions, applicable to the clinical realm:
1 unit of whole blood is about 450mL.
From several sources:
One unit of whole blood is equal to 450 milliliters or 0.950 pints. Blood collection centers usually measure it in mass rather than volume. The mass of one unit of blood is equal to 16.7 ounces. You can find more information here: www.unc.edu
Whole blood is normally divided into 4 components
Whole blood after donation is divided into
- red blood cell concentrates (PRBC = packed RBC)
- fresh frozen plasma
- platelet concentrates
Many other components are possible, but not typical. Here’s why they like to divide whole blood:
- Whole blood is more likely to carry disease.
- One unit of whole blood can be fractionated and provided to a number of individual instead of just one. For example, one unit of whole blood can be divided into a unit or packed cells, a unit of platelets, and a unit of fresh frozen plasma. Then, the plasma can be further fractionated.
- Most people require only one component.
- Components generally have greater shelf life than whole blood.
- Many blood products can be infused regardless of ABO blood type.
Here’s a bit about the components:
- PRBC = Packed Red Blood Cells are RBCs only. They are processed from whole blood or by RBC apheresis, where they’re known as “double reds,” because a donor can donate 2 units of RBCs. An average unit is 275-475mL. It can be stored for 35-42 days, when refrigerated properly.
- Plasma – known as “Fresh Frozen Plasma” (FFP), this is the liquid part of the blood. They remove many of the antibodies, as it can cause reactions, but it has some important coagulation factors, needed for those people who need help to clot their blood. One unit of FFP is between 200-400mL and has an expiration date of about 1 year.
- Platelets – the fragments of megakaryocytes may also be given to patients that have trouble clotting. One unit pheresis, from a single donor, is 175-500mL. If it’s closer to 500mL, they usually divide it to 2 bags. These are the most sensitive of the components and expire in 7 days.
- Cryoprecipitate – is prepared from plasma and contains fibrinogen and other clotting factors. It is the only one with enough fibrinogen, used to help with clotting, for IV use.
Question: I gave you three blood products above that are given to patients who have trouble clotting. Name a common drug that is given to patients to PREVENT clotting (I’ll list 3 names at the end of this blog).
- Granulocytes – these are WBCs. They don’t transfuse this much, but it is a possible product. One unit of granulocytes is about 225-400mL
Blood Splitting by Apheresis
Apheresis is a way to extract only a component, such as plasma, from a donor during the donation time. The whole blood from the patient is set to a machine which separates the wanted part from the blood and returns the rest of it back to the donor.
Plasma (plasmapheresis), platelets (plateletpheresis), red blood cells, and white blood cells can be separated by apheresis.
It’s a much longer donation process, and carries some risks, including a reaction to citrate, a chemical they add to prevent blood clotting. They often give donors calcium to prevent this.
- Heparin is injected IV or SubQ, not IM.
- Warfarin (trade name Coumadin, and others) is another drug that acts on the clotting factors and can be given in tablet forms (in the UK at least).
- Aspirin (medical abbreviation = ASA) is also used to prevent the clots that may lead to a heart attack.
Five more weeks left until break!