User:Lexicans/Blood Compatibility

There are 8 main, common blood types determined by the absence or presence of these antigens, each of which can trigger an incompatible immune response in the body if they are foreign to a patient’s body, these blood types are A+, A-, B+, B-, AB+, AB-, O+ and O-. Each individual person has an ABO blood groups and an Rh factor antigen which can be either positive or negative, inherited from our biological parents. Each parent donates one of their two ABO genes to their offspring. The A allele and B allele are dominant and the O allele is recessive. Rh factor is a protein found on the covering of red blood cells if a patient has this protein they are Rh positive. The Rh positive factor protein is dominant to the Rh negative gene. When a blood transfusion is required patients are usually given blood from someone from the same ABO and RhD group, however if unavailable or in an emergency situation a patient can be provided with blood from another group that won’t react with the immune system’s antibodies. It is vital that a compatible blood type is used on a patient to decrease the risk of organ failure.

On average 112.5 million units of donated blood is collected globally each year, with 47% of these donations collected in high-income countries that only contains 19% of the world population. Blood type distribution is vastly different for specific racial and ethnic groups. This is a worldwide population calculation.

Compatible Blood Types
Your ABO blood type group comes from the different antigens in the membrane of red blood cells. An antigen is anything that the immune system can respond to, in blood the antigens are sugars produced by reactions that enzymes catalyse the transfer of sugar molecules. If you have blood type A, the cells in your body make antibodies only for type B antigens, the A-type surface antigens on the cells are not recognised. The exact opposite is true for type B blood. If you are type O, your cells make antibodies against type A and type B antigens, this is why type O blood patients can only receive blood from other type O blood. Type AB blood means that the cells do not make any antigens against type A or type B surface antigens, this is why type AB blood can receive blood from any other ABO blood type and is the universal recipient The antigens of the blood transfused to a patient must be compatible with the patients antigens otherwise the antigens will attack each other.

The antigens that are expressed on the red blood cells determine the blood type. Antigen ABO determines blood types A, B, O and AB. The D antigen on the Rh red blood group system is the most important antigen, if you have the D antigen you are RhD positive and if you don’t you are RhD negative. RhD antigen determines if the blood type is positive or negative whether its Rh D-positive or Rh D-negative.

Rh+ can receive either Rh+ or Rh- where Rh- must receive Rh-. O- is the universal blood type that can be given to all patients regardless of their blood type. O- blood is frequently used in emergency situations where the blood type of a patient is unknown and if there is no time to undertake a compatibility test.

Blood compatibility in infants:
There are several reasons why babies and infants require a blood transfusion where an identifiable compatible blood type is required. Commonly babies require a blood transfusion because they have anaemia, when they have less red blood cells than normal. This can be a result of babies being born premature, have a medical problem, have had many blood tests already or have lost substantial amounts of blood in an operation. If an infants blood type not the same as mothers there is a risk of ABO blood type incompatibility, which is a type of illness known as haemolytic disease of the newborn (HDN). This can also occur if the mothers blood is Rh positive and the babies blood is Rh negative from the father. This problem usually occurs at delivery of the baby when the placenta detaches but may also happen during a miscarriage or abortion when the blood cells of the two circulations mix. A babies blood type may not match the mother is because blood types are determined from genes from each parent, with some blood types being dominant over others. Commonly ABO incompatibility occurs when a women that has type O blood (positive or negative) has a baby whose blood is type A, type B or type AB (positive or negative). This table identifies that O type blood is recessive to type A and B blood, this is why ABO blood incompatibility occurs.

Approaches to Compatibility Testing:
These measures need to be considered in the cross-matching laboratory, if blood was taken into a dry tube the blood needs to be clotted to avoid fibrin interfering the results, all information on specimen tube and form need to be cross checked to ensure it is all the same and importantly only one cross match for compatibility should be handled at one time to avoid confusion.

Techniques:

Antibody screening:
By the time you are six months old, your body naturally develops antibodies against the antigens that you are lacking in your red blood cells [1]. A person with A type blood with have anti-B antibodies and a person with B type blood will have anti-A antibodies A RBC antibody screen is used to detect these antibodies when a blood transfusion is required. Donor blood must not contain the corresponding antigens so that the red blood cell antigens do not destroy each other in the patient’s blood, for example if you have A type blood you cannot receive B type blood because your body’s anti-B antibodies will fight against the B blood type B antigens. These antibodies have the potential to cause harm to the patient if they are transfused with blood that the antibodies may target or if a pregnant mother has antibodies that could target the red blood cells of the developing baby.

Electronic cross matching:
A newer, more current technique of testing compatible blood types is electronic cross matching. Mostly used in larger laboratories with appropriate computer programs. To be able to do electronic cross matching you need ABO and RhD of the patients and 2 separate details of how to identify the patient (name, hospital, patient number), blood type and blood required for transfusion. It is a computer program that helps cross match compatible blood types and patients and also has a system that alerts for error and incompatibility [2]. The computer program stores the ABO and RhD type of the patients and the antibody screening results. The program will alert the operator for any errors and incompatible blood types. The ABO test of the patient should be done twice.

In the lab: ABO typing
To determine blood types, the blood sample from the patient will be mixed with antibodies that contain A and B type blood to observe how the blood responds to the antibodies. The sample is checked to determine if the red blood cells coagulate together. If they react it refers that the blood reacted with one of the antibodies present. Next back typing is performed, where the serum of the blood is mixed with identified type A and B blood. Patients with type blood A will have anti-B antibodies and the opposite for type B. Type O contains both anti-A and anti-B antibodies.

In the lab: Rh testing
A similar test is performed to determine the Rh factor on the surface of the red blood cells, if the patient has the Rh cell surface protein then their Rh positive, if they do not have the protein on the surface of the red blood cells they are Rh negative.

Compatibility Errors
Human error will always be a constant source of complications in any difficult task which can be minimised through policies and procedures in labs to ensure a reduction of inaccuracies in clinical laboratories, the smallest mistake can have catastrophic results to the patients. A common cause of errors in cross matching for blood compatibility is misidentifying of patient or the sample. Mistakes are most likely to occur in emergency situations where specimen taken may be incorrectly labelled with the wrong patient identifier, the wrong sample used in examination of blood type, and an incorrect unit of blood issued. This could all lead to the wrong blood type being identified for the patient which would lead to a wrong compatibility identification.

Several investigations of blood transfusion related deaths identified that 1/3 of these deaths and 2/3 of incompatible red blood cell transfusions were preventable. From 1976 to 1985, 355 deaths were reported by the US food and drug administration. Of these 355 deaths 99 were either unrelated to the transfusion itself or were a cause from transfusion caused hepatitis or AIDS. From the remaining 256 deaths, 51% were acute haemolytic transfusion reactions (AHTR). AHTR is a serious complication that occurs within the first 24 hours of a blood transfusion and initial symptoms include an increase temperature and pulse. Other symptoms include dyspnoea, body chills, discomfort on transfusion site, abnormal bleeding. A common cause of this is patients with blood type O (Rh positive or negative) receiving a blood transfusion from a patient with type A or B blood or Rh negative patients receiving Rh positive blood or in rare cases receiving a large volume of incompatible plasma. 15% of these deaths were a result from acute pulmonary injury which occurs within the first 6 hours of transfusion and symptoms include acute onset of fever, tachycardia and hypotension which can all lead to respiratory failure. 10% of these deaths were from bacterial contamination which includes human immunodeficiency virus (HIV), Staphylococcus strain and Yersinia enterocolitica   . 10% of these deaths was from delayed haemolytic transfusion reactions (DHTR) which occurs between 2 to 14 days after a blood transfusion, which has similar symptoms to AHTR however are much less severe and include jaundice and high levels of lactate dehydrogenase (LDH). The final 3% of deaths was from a damaged product.