Blood Group TypesCompatibility and Transfusions
This write-up was prompted by a related post asking about blood group compatibility: https://plus.google.com/100201577350898666331/posts/TJTTHpYRndvCONTENTS:| Types of Blood Products || ABO & Rh Groups |
- Universal recipient
- Universal donor| Blood Antigen Markers |
- Determining ABO designation: H antigen derivatives| Minor Blood Groups || Transfusion Preparation |
- Type & screen
- Type & cross-match
- Emergency casesCommon Blood Products
Whole, 2%, and skim (kidding)...
Whole blood used to be given for rapid and massive blood loss up until specific components were determined to be as clinically effective and more efficient in terms of supply management. Some components include packed red blood cells (pRBCs), fresh frozen plasma (FFP, which contains clotting factors), a more concentrated version of thawed and centrifuged FFP called cryoprecipitate, platelets, and others.
Separation permits judicious use of blood components, such as selective treatment using only pRBCs while conserving platelets to be used in a different patient, for example. It also allows different components to be packaged and stored under different conditions to maximize shelf-life.ABO and Rh Factor
Antigens are any cell fragment or molecule that antibodies can attach to and "flag" for eventual destruction by the immune system.
Major ABO and Rh blood group systems are highly emphasized because their antigens are the most immunogenic and pose a significant risk in terms of potential incompatible blood transfusion reactions.
AB blood type is the rarest and often cited as the "universal recipient" because those people lack antibodies targeted against A and B blood group antigens. In other words, A and B are not perceived as "foreign", and those individuals can handle all types (A, B, and O).
Blood type O is often considered the "universal donor" because those red blood cells do not have the potentially immunoreactive A and B antigens on them. Blood group O is the most common phenotype in the population at around 36-49% depending on race and ancestral place of origin.
Rh is named after the Rhesus monkey, and Rh factor commonly refers to the D antigen only even though there are around 50 antigens in the Rh group (this comes up often in obstetrics and pregnancy evaluation because of the transfer of blood between the mother and fetus). The presence or absence of the D antigen is the plus or minus designation seen after A, B, O, or AB (e.g., O+ or "O positive" is Rh positive O blood).Similar But Distinct Blood Antigen Markers
In normal scenarios, the O, A, and B antigens expressed on the surface of different RBCs are determined by 3 alleles located on chromosome 9. All antigens actually contain the same fundamental chain or base unit called the H antigen, and each varies by only one molecule.
If that oligosaccharide (short chain of carbohydrates) anchored to a protein on the RBC is unmodified, it is classified as "O" blood.
The "A" allele responsible for encoding a certain enzyme will add a molecule called N-acetylgalactosamine to transform the "O" chain (basic H antigen) into an "A" antigen instead. If the enzyme encoded by the "B" allele appends galactose (yes, the same natural sugar commonly found in milk), the "O" chain then becomes a "B" antigen. Basic ABO antigen structures are illustrated in Figure 11.17 here http://www.ncbi.nlm.nih.gov/books/NBK22396/#A1530Minor Blood Groups
In reality, aside from ABO and Rh, there are many minor blood group antigens too. There are 30 other blood group systems,
each of which has several sub-types. Of the minor groups, some of the more memorable ones are named after the patients whom they were first discovered in, such as Kell, Kidd, Duffy, Lewis, etc. It is thought that some minor blood groups may have arose due to evolutionary advantages. For example, some people lacking the Duffy antigen demonstrate resistance to certain species of malaria.
Relatively fewer people deal with these details on a day-to-day basis or are expected to remember the exact specifics, such as pathologists and technicians who work in the blood bank of a hospital. Nonetheless, these lesser-known minor antigens exist and are important.
• More info from Blood Groups and Red Cell Antigens: http://www.ncbi.nlm.nih.gov/books/NBK2261/
• A list of blood groups: http://en.wikipedia.org/wiki/Human_blood_group_systems#Blood_group_systemsWhat the Doctor Ordered: Type, Screen, and Cross-match
In medicine, there are a couple ways to order blood to prepare for transfusions. For routine elective surgical procedures (i.e., planned, not an emergency) where minimal blood loss is expected, doctors can order a "type and screen". This means they identify the major type of blood group of the patient and screen for clinically significant antibodies in the recipient's serum. This is done out of precaution and gives a heads-up to the blood bank to let them know the blood may
be required, but is not anticipated to be needed. It's also a preliminary and less intensive way to analyze blood because IF no unexpected RBC antibodies are present in the patient, then the extremely detailed identification of possibly hundreds of minor antigens in donor blood is not necessary. For those who qualify, blood can be given based on just ABO and Rh typing.
In other cases where blood products will be definitely administered (e.g., symptomatic anemia or active uncontrolled but slow bleeding), doctors request a "type and cross". The typing identifies the major blood group as before, and the full "cross-matching" goes into much deeper analysis to match up donor and recipient for all the clinically relevant minor antigens.
Of note, the addition of a cross-match to a "type and screen" (ABO/Rh typing and antibody screening) increases detection of incompatibility by only 0.01%. However, since millions of transfusions are performed, that 0.01% is not necessarily insignificant.In the Case of an Emergency
In urgent situations (e.g., hemorrhagic shock) where the correct ABO type is in doubt or unknown and the doctor cannot wait for a full cross-match, O- (O Rh-negative) blood is given. In life-threatening emergencies where Rh-negative blood is unavailable, giving Rh positive blood is not off limits (the apparent reaction can be medically managed in other ways, whereas the immediate life-threatening cause can only be managed with a few options).
A "type and screen" can take up to ~10 minutes, and a "type and cross-match" could take on the order of an hour. If they don't have 60 or even 10 minutes to spare, they start to administer the "universal donor" blood up front (while continuing to cross-match). This scenario does not happen as often, though, and is more likely to occur during disaster response situations or accidents involving severe injuries.Related:
• Facts about blood use and donations: http://www.redcrossblood.org/learn-about-blood/blood-facts-and-statistics
• Mosquitoes may tend to prefer blood type O:
- http://scienceline.org/2007/09/ask-knight-mosquitoes/ #ScienceEveryday #BloodType #Transfusions Public Domain image from Wikipedia.