About the Test
Purpose of the test
Blood typing may be used to:
- Ensure ABO and Rh compatibility between your blood type if you require a transfusion of blood or blood components and the unit of blood that will be transfused. While ABO and Rh are the most important, there are many other blood group systems that have to be considered. In addition to ABO/Rh typing, other tests such as a red blood cell (RBC) antibody screen and a crossmatch are performed to determine what type of blood or blood components you can safely receive.
- Determine compatibility between a pregnant woman and her developing baby (fetus). Rh typing is especially important if you are pregnant because you and your fetus could be incompatible. If you are Rh-negative but the father is Rh-positive, the fetus may be positive for the Rh antigen. Because Rh is an antigen, it can elicit an immune response and you could develop antibodies against the Rh antigen. These antibodies can cross the placenta and destroy the baby’s red blood cells, resulting in hemolytic disease of the fetus and newborn (HDFN).
- 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 for use by people that require a specific ABO group and Rh type.
- Determine the blood group type of potential donors and recipients of organs, tissues, or bone marrow, as part of a workup for a transplant procedure. In addition to blood typing, there is another system of proteins (antigens) found on most cells of your body (but not usually red blood cells) that play an important part in responding to foreign substances. These antigens vary from person to person and are known as human leukocyte antigens (HLA). 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 antigens.
What does the test measure?
Blood types are based on the markers (specific carbohydrates or proteins) or antigens on the surface of red blood cells (RBCs). Two major antigens or surface identifiers on human RBCs are the A and B antigens. Another important surface antigen is called Rh. A lab test for blood type detects the presence or absence of these antigens in determining your ABO blood group and Rh type.
People whose red blood cells have:
- A antigens are in blood group A
- B antigens are in blood group B
- Both A and B antigens are in blood group AB
- Neither of these markers is in blood group O
If the Rh protein is present on the red blood cells, your blood type is Rh-positive; if it is absent, your blood is type Rh-negative.
Our bodies naturally produce antibodies against A antigens if you are blood type B, and antibodies against B antigens if you are blood type A. If you are blood type AB, you will not have antibodies against A or B. Because of this, an AB+ person can receive AB+ blood, A+ blood, or B+ blood. And those with blood type O will have antibodies against both A and B.
The following table indicates the type of antibodies you are expected to have based on your blood type.
| A PERSON WITH BLOOD TYPE | WILL HAVE ANTIBODIES TO |
|---|---|
| A | B antigen |
| B | A antigen |
| AB | Neither antigen |
| O | A and B antigens |
These antibodies are useful for determining a person’s blood type and the types of blood they can safely receive (compatibility).
For example, if you are a group A person, you have antibodies directed against the B antigen. If you are transfused with type B blood, your antibodies would target and destroy the transfused B+ red blood cells. This can cause severe, potentially fatal complications. Thus, it is critical to match a person’s blood type with the blood that is to be transfused.
Rh-factors are genetically determined. A baby may inherit the Rh-factor from either parent or a combination of both. Unlike antibodies to A and B antigens, antibodies to Rh are not produced naturally. Antibodies that are produced against the Rh factor can develop only if you lack the Rh factor on your red blood cells and then you are exposed to Rh-positive red blood cells.
This can happen during pregnancy or birth when the mother is Rh-negative and the baby is Rh-positive, or sometimes when you are Rh-negative and are transfused with Rh-positive blood.
In either case, the first exposure to the Rh antigen may not result in a strong response against the Rh-positive cells, but any subsequent exposure such as a second pregnancy may cause severe reactions.
When should I get blood typing?
ABO grouping and Rh typing are sometimes automatically performed, such as anytime someone donates blood. Typing of donated blood is important because this information allows health care practitioners to determine which patients are compatible and can safely receive that blood.
In addition, there are a few times when it may be necessary for you to get a blood typing test.
Blood transfusion patients: If you are receiving a blood transfusion, you will need your blood type confirmed through a blood typing test. The only time you would not get a blood type test is in an extreme emergency lacking 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.
Conditions or situations that may warrant a transfusion include:
- Bleeding during or after surgery
- Injury or trauma due to excessive blood loss
- Cancer and the effects of chemotherapy
- Severe anemia and conditions causing anemia thus requiring frequent transfusions as experienced with sickle cell disease and thalassemia
- Bleeding disorders such as hemophilia
Organ, tissue or bone marrow transplant recipients or donors: Blood typing may be ordered when you become a candidate for an organ, tissue, or bone marrow transplant, or when you wish to become a donor. It is one of the first of many tests used when determining whether a potential donor and recipient are compatible.
Pregnant women: Testing is ordered when you become pregnant to determine whether you are Rh-negative or -positive. All newborn babies of Rh-negative mothers are typed for ABO and Rh soon after birth. This determines if the mother needs to receive Rh immune globulin, which prevents her from developing antibodies against her fetus’ blood cells.
To determine if people are related: Sometimes blood typing may be done as part of the process for determining whether someone could be a blood relative such as paternity cases.
Forensic testing in identifying a blood type from a blood stain sample taken from a crime scene.
If you have a desire to find out your blood type, you can ask your doctor or laboratory to check your past blood work records. You can also find out if you become a blood donor.
Finding a Blood Typing Test
How can I get a blood typing test?
In most cases, blood typing will be ordered by a doctor if you are a donor or recipient of a transfusion or organ transplant, or if you become pregnant. Blood typing will be automatically done when donating blood, and you can request the results be sent to you.
However, you can also request a blood typing test if you’re just curious or have a personal reason for wanting to discover your blood type. You should be able to get tested by your doctor, though you may have to pay out-of-pocket if there is a non-medical reason for your test.
You may also order a blood typing test online and set an appointment for testing by a Clinical Laboratory Improvement Amendments (CLIA)-approved laboratory.
Can I take the test at home?
It is possible to take a blood typing test at home using an at-home test kit. These kits come with a lancet to prick your finger and draw a blood sample. It will also have a card to place the blood sample on. How the blood reacts and appears will indicate your blood type. Be sure to follow the instructions carefully so that you get the most accurate result possible. When done correctly, you can expect to receive 99.9% accuracy in results.
Another option is to order a blood typing test online and have your sample collected at a local lab.
How much does the test cost?
For most situations when you’d need a blood typing test, it is a medical necessity and will usually be covered by health insurance. If you’re a donor, you will not have to pay anything out of pocket to find out your blood type (though it may take a couple of weeks to get results).
If you request a blood typing test on your own; however, you will likely have to pay for it out-of-pocket.
Prices vary depending on where the test is done or where you order a test kit from. If you are covered by insurance, you may be required to make a copayment or deductible payment depending on your plan. Your health care provider, laboratory, or test kit company should be able to give you an estimate of the cost.
Taking a Blood Typing Test
A sample of blood is drawn from a vein or from the tip of the finger. In newborns, blood from the umbilical cord or a small amount of blood from a heelstick may be used for testing.
Before the test
No preparation is needed for this test other than sterilizing the area with an alcohol pad before you draw blood.
During the test
To collect your blood sample, a phlebotomist will draw blood from a vein in your arm. They will start by tying an elastic tourniquet around the upper part of your arm and may have you make a fist to help the vein stand out. Next, they’ll cleanse the vein area with an alcohol wipe and allow the area to dry. Then a vacuum-collection tube with a needle is inserted into your vein to collect blood into a vial.
You may feel a slight pinch when the needle is first inserted. When the phlebotomist withdraws the needle, they will use a gauze pad to apply pressure to the site and cover it with a bandage. The entire blood draw shouldn’t take more than a couple of minutes.
Taking an at-home blood typing test involves a fingerstick using a tiny needle called a lancet. After cleansing a finger with alcohol and allowing it to dry, the lancet is used to prick the finger. The finger is then gently squeezed to obtain a few drops of blood and placed on the designated spots on the collection card. It is very important to follow the directions in collecting the specimen and to help you interpret the results. Test kit instructions may vary, so be sure to review the instructions before you move forward.
After the test
Other than keeping your bandage on for a little while to ensure that there is no bleeding, there are no restrictions after the test. You may have a slight bruise at the blood draw site. If using the fingerstick method, cover the wound with a bandage to prevent an infection and allow it to heal quickly.
Blood Typing Test Results
Receiving test results
Non-emergent blood typing test results obtained from a laboratory are generally available in a short amount of time, usually a day or so. Emergency transfusion results performed in a hospital laboratory are usually available within minutes. When doing an at-home test, your testing kit will specify how long to wait to look at the test card for results, but it’s also usually in just a few minutes.
If you are donating blood, you can request that your blood type results be shared with you, but it may take a couple of weeks to receive them by mail.
Interpreting test results
The results of blood typing will determine if you are type A, B, AB, or O and if you are Rh-negative or -positive. The results will tell the health care provider what blood or blood components will be safe for you to receive if necessary.
The following table shows what types of blood patients can safely receive, based on their individual blood types.
| 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. See the article on Transfusion Medicine for more on this.
Depending on your results and the reason for your testing, you may have questions for your doctor. These may include:
After you get your result:
- Will my blood type be easy to match if I ever need a donation?
- Is my blood type in high need of donations?
- Does my blood type put me at any type of health risk?
If you’re pregnant:
- What are the next steps if I test Rh-negative?
Resources
- Association for the Advancement of Blood & Biotherapies: FAQs About Blood and Blood Donation
- American Red Cross: Facts About Blood and Blood Types
- National Heart, Lung, and Blood Institute: Treatments for Blood Disorders
- National Heart, Lung, and Blood Institute: Blood Tests
- UNOS Transplant Living: Tests for Living Donation
- Vitalant Blood Donation: Blood and Blood Types
- LifeShare: General Blood Donation Questions
