A Lot in a Drop 🩸

In transfusion medicine, or immunohematology, Medical Laboratory Scientists serve patients that are anywhere from extremely critical and needing products ASAP, to routine sickle cell and cancer patients.

Here’s how the standard ABO blood type is performed by tube method. We’ll use an AB positive patient as an example.

ABO proteins are important because we make naturally occurring antibodies to them. These react strongly if blood isn’t matched correctly. There are two parts to the test that must match: forward and reverse type.

In forward typing (the first four tubes from left to right), we test for the presence of A and B antigens on the surface of red blood cells (RBCs). A sample of the patient's RBCs is mixed with anti-A and anti-B reagents.

🩸 When mixed with Anti-A reagent, agglutination (clumping) occurs because the A antigen is present on the RBCs.

🩸 Similarly, when mixed with Anti-B reagent, agglutination occurs due to the presence of the B antigen.

🩸 In the case of Anti-D reagent (used to detect the Rh factor, or what determines if you’re positive or negative), agglutination will also occur, confirming the presence of the D antigen, indicating Rh positivity.

🩸 An AB positive person’s RBCs will agglutinate with all three reagents (anti-A, anti-B, and anti-D).

The reverse type (the last two tubes) acts as an internal check that testing is done correctly. Both halves should match. Reverse typing checks for antibodies in the patient’s plasma against A or B antigens. The patient’s plasma is mixed with type A and type B RBCs.

🩸 Since an AB positive person has both A and B antigens on their RBCs, they do not have anti-A or anti-B antibodies in their plasma.

🩸 Therefore, no agglutination will occur when their plasma is mixed with type A or type B RBCs.

For an AB positive patient, they are known as universal plasma donors and universal RBC recipients because they can receive any type of RBCs, making them versatile in transfusion scenarios. Since their plasma carries no Anti-A or Anti-B antibodies, it is safe to use with other patients. However, AB patients can only receive AB plasma.

Confused yet?

Here’s another look with a B positive patient.

Just be thankful we have amazing behind the scenes heroes that have this down to a science!!