help remembering blood types and lab values

Think of the "O" as zero. There are zero reasons why the "O" donor cannot give blood to anyone else. All types can get "O" donated to them. The rest can only have their own letter. So, "A" recipient can only have "A" or "O", "B" recipient can only have "B" or "O"------

As for Rh factor - positive can positively have negative blood as well as positive. Negative recipients can only have negative.

You might have to come up with your own style of memorization.

Lab values - try more than one way to memorize. Use visual (see it written), audio (hear it said, say it out loud) and tactile (write it down).

There was a similar question a while back and I wrote a very lengthy response here:

https://allnurses.com/general-nursing-student/blood-compatibility-674430.html

Once you fully understand what's going on physiologically with transfusions and transfusion reactions, you won't need any "tricks" to remember.

Type O is the universal donor because people with type O blood do not have either antigen (A or B) on the surface of their red blood cells, therefore there is nothing for the recipient to react to. Type AB is the universal recipient because they have both antigens on the surface of their red blood cells and therefore do not have antibodies against either.

Considering the Rh factor, Rh positive recipients can receive either Rh positive or Rh negative blood. Rh negative patients cannot receive Rh positive blood because the body will recognize the Rh factor as foreign and mount an immune response/start building antibodies against it. This is when Rh negative women need to get Rhogham if they carry an Rh positive baby... if their blood comes in contact with the baby's during delivery or at any time during pregnancy, it will begin forming antibodies against the Rh factor and any future pregnancies with an Rh positive fetus would be in jeopardy because the body would have antibodies against the Rh factor and attack it. Look up erythroblastosis fetalis.

I found it helped me more to understand the "whys" rather than to do straight memorization. Why do you need to be careful about donor and recipient blood type? Think about the antibodies, what happens when, say, anti-A antibodies attack A blood cells. Which antibodies does each blood type have?

O is considered a universal donor because the O blood cells have no A or B antigens on their surface, so recipient blood will not attack the new blood cells. AB blood has no antibodies in it, so they can accept A, B, or O blood.