How a Blood Typing Test is Done
1. In a blood typing tray, place a few drops of someone's blood into each well.  This is where we will test for A antigens, B antigens, and the Rh factor. (We will not test for Rh factor in today's lab, but that is where the + or - label comes from in blood types).

2. Place a drop of "anti-A" serum in well A.

3. Place a drop of "anti-B" serum in well B.

4. Stir each with a clean toothpick, do not cross-contaminate!
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5. Observe.  If the antigens are present, the blood will react with the anti-A or anti-B solution.  You will see some separation and clumping showing the proteins are present.
How to Read a Blood Typing Tray
The sample above shows there are antigens in well B.  This sample is positive for B antigens, but does not have A or Rh factor.  This person would have the blood type B-.