Blood typing – Uses, Indications, Procedure, Result

Blood typing is a method to tell what type of blood you have. Blood typing is done so you can safely donate your blood or receive a blood transfusion. It is also done to see if you have a substance called Rh factor on the surface of your red blood cells.

Your blood type is based on whether or not certain proteins are on your red blood cells. These proteins are called antigens. Your blood type (or blood group) depends on what types your parents passed down to you.

Cross-matching; Rh typing; ABO blood typing; Blood group; Anemia – immune hemolytic blood type; ABO blood type; A blood type; AB blood type; O blood type

Blood typing is a method to tell what type of blood you have. Blood typing is done so you can safely donate your blood or receive a blood transfusion. It is also done to see if you have a substance called Rh factor on the surface of your red blood cells.

Your blood type is based on whether or not certain proteins are on your red blood cells. These proteins are called antigens. Your blood type (or blood group) depends on what types your parents passed down to you.

Blood is often grouped according to the ABO blood typing system. The 4 major blood types are:

  • Type A
  • Type B
  • Type AB
  • Type O

How the Test is Performed

A blood sample is needed. The test to determine your blood group is called ABO typing. Your blood sample is mixed with antibodies against type A and B blood. Then, the sample is checked to see whether or not the blood cells stick together. If blood cells stick together, it means the blood reacted with one of the antibodies.

The second step is called back typing. The liquid part of your blood without cells (serum) is mixed with blood that is known to be type A and type B. People with type A blood have anti-B antibodies. People with type B blood have anti-A antibodies. Type O blood contains both types of antibodies.

The 2 steps above can accurately determine your blood type.

Rh typing uses a method similar to ABO typing. When blood typing is done to see if you have Rh factor on the surface of your red blood cells, the results will be one of these:

  • Rh+ (positive), if you have this substance
  • Rh- (negative), if you do not have this substance

How to Prepare for the Test

No special preparation is necessary for this test.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

Blood typing is done so you can safely receive a blood transfusion or a transplant. Your blood type must closely match the blood type of the blood you are receiving. If the blood types do not match:

  • Your immune system will see the donated red blood cells as foreign.
  • Antibodies will develop against the donated red blood cells and attack these blood cells.

The 2 ways that your blood and the donated blood may not match are:

  • A mismatch between blood types A, B, AB, and O. This is the most common form of a mismatch. In most cases, the immune response is not very severe.
  • Rh factor may not match. The immune response can be much more severe.

Blood typing is very important during pregnancy. Careful testing can prevent severe anemia in the newborn and jaundice.

Normal Results

You will be told which ABO blood type you have. It will be one of these:

  • Type A blood
  • Type B blood
  • Type AB blood
  • Type O blood

You will also be told whether you have Rh-positive blood or Rh-negative blood.

Based on your results, your health care providers can determine which type of blood you can safely receive:

  • If you have type A blood, you can only receive types A and O blood.
  • If you have type B blood, you can only receive types B and O blood.
  • If you have type AB blood, you can receive types A, B, AB, and O blood.
  • If you have type O blood, you can only receive type O blood.
  • If you are Rh+, you can receive Rh+ or Rh- blood.
  • If you are Rh-, you can only receive Rh- blood.

Type O blood can be given to anyone with any blood type. That is why people with type O blood are called universal blood donors.

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

  • Fainting or feeling lightheaded
  • Multiple punctures to locate veins
  • Excessive bleeding
  • Hematoma (blood buildup under the skin)
  • Infection (a slight risk any time the skin is broken)

Considerations

There are many antigens besides the major ones (A, B, and Rh). Many minor ones are not routinely detected during blood typing. If they are not detected, you may still have a reaction when receiving certain types of blood, even if the A, B, and Rh antigens are matched.

A process called cross-matching followed by a Coombs test can help detect these minor antigens. It is done before transfusions, except in emergency situations.

Common Questions

How is it used?

Blood typing is used to determine an individual’s blood group, to establish whether a person is blood group A, B, AB, or O and whether he or she is Rh positive or Rh negative.

Blood typing may be used to:

  • Ensure compatibility between the blood type of a person who requires a transfusion of blood or blood components and the ABO and Rh type of the unit of blood that will be transfused. Blood typing is performed in conjunction with other tests such as an RBC antibody screen and a crossmatch to determine what type of blood or blood components the person can safely receive. A potentially fatal transfusion reaction can occur if a unit of blood containing an ABO antigen to which the blood recipient has an antibody is transfused to the recipient. For example, people with blood group O have both anti-A and anti-B antibodies in their blood. If a unit of blood that is group A, B, or AB is transfused to this person, the antibodies in the recipient’s blood will react with the red blood cells, destroying them and causing potentially serious complications.Similarly, if an Rh-negative individual is transfused with Rh-positive blood, it is likely that the person will produce antibodies against Rh-positive blood. Although this situation does not cause problems for the recipient during the current transfusion, a future transfusion with Rh-positive blood could result in a serious transfusion reaction.
  • Determine compatibility between a pregnant woman and her developing baby (fetus). Rh typing is especially important during pregnancy because a mother and her fetus could be incompatible. If the mother is Rh negative but the father is Rh positive, the fetus may be positive for the Rh antigen. As a result, the mother’s body could develop antibodies against the Rh antigen. The antibodies may cross the placenta and cause destruction of the baby’s red blood cells, resulting in a condition known as hemolytic disease of the fetus and newborn (HDFN). To prevent development of Rh antibodies, an Rh-negative mother is treated with an injection of Rh immune globulin during her pregnancy and again after delivery if the baby is Rh-positive. The Rh immune globulin binds to and “masks” the fetus’s Rh antigen during pregnancy and delivery and prevents the mother from developing antibodies against the Rh antigen.
  • Determine the blood group of potential blood donors at a collection facility. Units of blood collected from donors are blood typed and then appropriately labeled so they can be used for people that require a specific ABO group and Rh type.
  • Determine the blood group of potential donors and recipients of organs, tissues, or bone marrow, as part of a workup for a transplant procedure. Along with HLA testing, ABO blood typing is used to identify and match organ and tissue transplant donors with recipients who have the same or an acceptable number of matching HLA genes and antigens.

When is it ordered?

ABO grouping and Rh typing are performed on all donated blood. They are also performed when people require blood transfusion. Conditions or situations that may warrant a transfusion include:

  • Severe anemia and conditions causing anemia such as sickle cell disease and thalassemia
  • Bleeding during or after surgery
  • Injury or trauma
  • Excessive blood loss
  • Cancer and the effects of chemotherapy
  • Bleeding disorders such as hemophilia

Testing is ordered when a woman becomes pregnant to determine whether she is Rh negative or positive. All newborn babies of Rh-negative mothers are typed for ABO and Rh soon after birth to determine if the mother needs to receive Rh immune globulin.

Blood typing may be ordered when a person becomes a candidate for an organ, tissue, or bone marrow transplant, or when a person wishes to become a donor. It is one of the first of many tests used when determining whether a potential donor and recipient are compatible.

Sometimes blood typing may be done as part of the process for determining whether someone could be a blood relative.

What does the test result mean?

The results of blood typing will determine if a person is type A, B, AB, or O and if he or she is Rh negative or positive. The results will tell the healthcare provider what blood or blood components will be safe for the person to receive.

The following table shows what types of blood patients can safely receive, based on their individual blood type.

Blood Group and Rh Type of Patient Safe (Compatible) Blood Types for RBC Transfusion*
A positive A positive, A negative, O positive, O negative
A negative A negative, O negative
B positive B positive, B negative, O positive, O negative
B negative B negative, O negative
AB positive AB positive, AB negative, A positive, A negative, B positive, B negative, O positive, O negative
AB negative AB negative, A negative, B negative, O negative
O positive O positive, O negative
O negative O negative

*These apply for RBC transfusions only; when transfusing plasma products and platelets, the compatible choices are different.

Blood typing results will show whether a pregnant woman is Rh positive or negative. This information will indicate whether she may be a candidate for receiving Rh immune globulin, which would prevent her from developing antibodies against her fetus’ blood cells.

Typing of donated blood is important because this information allows healthcare practitioners to determine which patients are compatible and can safely receive that blood.

Similarly, when a donor organ, tissue, or bone marrow is compatible with the intended recipient, it is less likely to be rejected in the immediate post-transplant period.

Is there anything else I should know?

The following table summarizes the approximate distribution of blood groups and types in the U.S. population:

BLOOD TYPE RH POSTIVE RH NEGATIVE TOTAL
O 39% 9% 48%
A 30% 6% 36%
B 9% 2% 11%
AB 4% 1% 5%
TOTAL 82% 18% 100%

Although Rh incompatibility has more severe consequences, one of the most common causes of hemolytic disease of the fetus and newborn (HDFN) is actually an incompatibility between the mother’s and baby’s ABO blood groups, not the Rh factor. However, ABO grouping cannot be used to predict whether HDFN will occur because antibodies to the ABO blood groups are naturally occurring.

Besides A and B, many other antigens exist. Having a rare blood type is especially problematic if you need repeated transfusions, as sickle cell anemia and thalassemia patients do. If blood transfusions are not closely matched to blood types of patients, they may suffer transfusion reactions. Such reactions are less likely if donors and recipients are from the same racial or ethnic groups. Molecular testing techniques that analyze a person’s genes may be used to predict the presence of unusual or uncommon red cell antigens.

Do I need to know my blood type?

If you need a transfusion, healthcare practitioners at your health care facility will determine your blood type before they give you any blood. The only time you would not get a blood type test is in an extreme emergency and there is not enough time to type your blood. In this case, you would receive group O since this blood type does not have any A or B antigens that can potentially cause a hemolytic transfusion reaction. The use of Rh-negative blood depends upon the situation and the supply of O negative blood in the area.

Who are universal blood donors and recipients?

Universal blood donors have type O, Rh-negative blood. This means they have no A or B antigens or Rh factor on their red blood cells to which the recipient’s antibodies can react. Recipients of their red blood cells have little risk of a hemolytic transfusion reaction due to ABO or Rh incompatibility.

Universal recipients have type AB, Rh-positive blood. They recognize A, B, and Rh antigens as “self” and can receive red blood cells of any ABO or Rh type with no risk of a serious hemolytic transfusion reaction due to ABO or Rh incompatibility.

Besides ABO and Rh, are there other types of red blood cell antigens?

Yes, numerous other antigens can be present on the surface of red blood cells. These other RBC blood group antigens include, for example, Kell, Kidd, Duffy, and other Rh antigens. The body does not produce antibodies to these antigens unless it is exposed to these antigens through blood transfusion or during pregnancy. These antibodies are not detected during routine blood typing but may be found with an RBC antibody screen.

References

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