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Finding out your blood type is relatively simple. You can:
- have your doctor order a test
- get the information when donating blood
- take an at-home blood test
Your blood type is comprised of two blood groups: ABO and Rh.
Blood types are based on antigens on the surface of your red blood cells. An antigen is a substance that triggers an immune response by your body against that substance.
The presence of specific antigens designates ABO blood types:
- Type A has the A antigen
- Type B has the B antigen
- Type AB has both the A and B antigen
- Type O has neither the A nor B antigen
Once your ABO blood type has been determined, it can be further defined by identifying the Rhesus (Rh) factor:
- Rh-positive. If you have Rh antigens on the surface of your red blood cells, you have Rh-positive blood.
- Rh-negative. If you don’t have Rh antigens on the surface of your red blood cells, you have Rh-negative blood.
By including the Rh factor, the 8 most prevalent blood types can be identified: A+ or A-, B+ or B-, AB+ or AB-, and O+ or O-.
A phlebotomist (someone trained to draw blood) will use a needle to draw blood from your arm or hand at your doctor’s office, a clinical laboratory, or a hospital
The typical method for typing blood involves two steps:
- forward typing
- reverse typing
The first step is called “forward typing.” Your blood cells are mixed with antibodies against type A and B blood, and the sample is checked to see whether the blood cells stick together (agglutinate).
If blood cells stick together, it means your blood cells reacted with one of the antibodies.
For example, if your blood cells agglutinate when mixed with antibodies against type B blood (“anti-B antibodies”), you have type B blood.
The second step is called “back typing” or “reverse typing.” The liquid part of your blood without red blood cells (serum) is mixed with blood cells that are known to be type A and type B.
People with type A blood have antibodies against Type B blood (“anti-B antibodies”) in their serum, and those with type B blood have antibodies against Type A blood (“anti-A antibodies”) in their serum.
Type O blood contains both anti-A and anti-B antibodies.
So, for example, if agglutination occurs when your serum is mixed with type B blood cells, you have type A blood.
Summary and Rh typing
ABO testing should include both forward and reverse typing. The result from forward typing is the patient’s blood type. Reverse typing is a cross-check for forward typing and provides confirmation of results.
Next, your blood will be mixed with an anti-Rh serum. If your blood cells respond by clumping together, you have Rh-positive blood.
In at-home blood typing tests, they typically ask that you prick your finger with a lancet and put drops of your blood on a special card.
After putting the blood on the card, you can observe the areas where blood clumps or spreads out, and then match those reactions to an included guide.
Some home testing kits have vials of fluid for your blood, as opposed to a card.
One way to find out your blood type is to donate blood.
If you donate to community blood supplies, ask the staff if they’ll be able to tell you your blood type. Many donation centers are able to provide that information.
Typically, you won’t get your blood type immediately and may have to wait a few weeks, as blood isn’t commonly tested right away.
Secretors can have their blood type determined by a saliva or other body fluid test.
Blood typing kits using saliva are available online, but they’re typically more expensive.
Using one of the kits, you’ll first learn whether you’re a secretor. If you are, then you’ll be able to determine you ABO blood type.
There are a number of ways you can determine your blood type, including:
- visiting your doctor
- going to a hospital or clinical laboratory that tests blood
- donating blood
- getting a home testing kit
If you’re in the category of people who secrete blood-group antigens in other body fluids, you may be able to find out your blood type without having blood drawn.