How to Grade Antibody Reactions

Antibody reactions occur when a particular antigen is exposed to an antibody. An antigen-antibody reaction test is used to determine a person's blood type for blood banking or it can also be used in an emergency situation when a patient is in need of blood donor. The reaction that occurs when the blood is mixed with the reagents can be graded. Any sign of aggregates -- or clumping in the tube -- signals a positive reaction. This test is also known as Coombs' test.

Things You'll Need

• Tube blood
• Transfer pipette
• Lighted agglutination viewer
• Saline bottle
• Centrifuge tube
• Centrifuge
• Antibody

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Instructions

• 1

  Collect a fresh blood sample using proper phlebotomy techniques.

• 2

  Wash the red blood cells to obtain a 3 percent suspension.

• 3

  Use a transfer to place 1 to 3 drops of blood into an autoclaved centrifuge tube.

• 4

  Aim the tip of the saline bottle towards the center of the tube and forcibly squirt saline into the tube. Fill it 3/4 full of saline.

• 5

  Place the cap on the tube and use a centrifuge to spin the cells into a button in the bottom of the tube.

• 6

  Use a transfer pipette to decant the saline completely, being careful not to disturb the button of cells on the bottom of the tube. You may need to repeat this wash depending on the antibody reaction.

• 7

  Add the appropriate antibody or prepared sample.

• 8

  Use a lighted agglutination viewer and position the tube, so that reflection of the bottom of the tube can be easily seen.

• 9

  Swirl the tube in your hand to re-suspend the cells, and watch the tube carefully.

• 10

  Grade the reaction according to the following criteria:

  A solid clump would be graded as a 4+.

  Several large clumps would be graded as a 3+.

  Small to medium sized clumps with a clear background would be graded as a 2+.

  Small clumps with a cloudy background wound be a 1+.

  If there are only tiny aggregates and a cloudy background the reaction would be graded as a +w.

  If the aggregates are only visible upon microscopic examination, it would be graded as a + micro.

  If there are small clumps amidst many agglutinated cells, it would be considered mixed field and graded as MF.

  Hemolyzed or hem would indicated a positive reaction, while neg would indicate a negative reaction.