The page below is a sample from the LabCE course Introduction to the ABO Blood Group System. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Reverse Typing

Reverse typing refers to the testing of a patient's serum for the presence of ABO antibodies. The patient's serum is mixed with known red cells in a test tube. A specified number of drops of patient serum are placed into each of three properly labeled tubes. A specified number of drops of known A1 cells are added to the A tube, and a specified number of drops of known B cells are added to the B tube.

The tubes are mixed by gently shaking, centrifuged, and observed against a well-lit white background for the presence of hemolysis in the supernatant fluid. The cell button is then gently dispersed and inspected for agglutination, again using a well-lit background. Hemolysis or agglutination is a positive reaction. The expected reactions can be seen in the table on the following page.