Quick explanation of ABO/Rh blood type testing: To understand how this kind of blood typing test works, you will need to (a) understand what antibodies are and how they function and (b) what agglutination is. The photo above shows a slide with 4 SEPARATE blood drops (from the same person). EACH of these four blood drops has been mixed with a liquid containing ONE antibody type (which are different for each blood drop).
Background:
(a) What is an antibody and HOW does it function in ABO/Rh blood typing?
Antibodies are Y-shaped proteins that are, as you probably know, important players in the immune system. In the immune system, antibodies "flag" foreign-looking molecules (called "antigens"). This flagging helps to signal ("recruit") certain other immune cells to destroy the foreign-looking thing, because that foreign-looking thing might be toxic, or be attached to something toxic/harmful.
Antibodies have a special physical property: they can be made in "batches" that are extremely specific to only be able to "flag" ONE kind of antigen (some small molecule), such as those on the surface of red blood cells in humans. In blood typing, we can take advantage of this physical "specificity" property that antibodies have. The common antigens found on red blood cells in humans are "A" antigens, "B" antigens, and Rh factor antigens. We can MAKE antibodies to EACH of these antigens, respectively, and use them for blood typing. (See Link 1 below for video and further details).
(b) What is agglutination?
*To be added*
What is the basic set-up for blood typing?
The basic set-up FOR EACH DROP OF BLOOD is this: drop of blood from ONE person + ONE drop of liquid containing one type of antibody that only sticks to a certain, known antigen. For example, let's consider the first liquid drop in the photo, starting from the left (i.e. the drop labeled "anti-A"). What, specifically, is in that first liquid drop? This "anti-A" labeled liquid drop contains two things: drop of blood (hence, red blood cells) + antibodies that are *specifically* AGAINST human "A" antigen (little molecules that can be found sticking out in many places on the cell surface of red blood cells of people who have either type A blood or type AB blood).
The story about agglutination here is that the anti-A antibody will ONLY "stick" to human "A" antigens that this antibody "sees"/runs into when type A or type AB blood is mixed with a liquid solution full of anti-A antibodies. This "sticking" of anti-A antibody to "A" antigen on the surface of red blood cells is another way of saying a direct agglutination reaction is occurring. In the case of blood typing, a common class of antibody called IgM is used because this class of antibody has a shape that allows it to "stick to" many red blood cells at the same time, thus bringing about VERY fast clumping/agglutination reaction if the correct antigen ("A" in this case) is present that corresponds to the antibody (in case, anti-A antibody). Thus, if no "A" antigens are present on the red blood cells in the presence of anti-A antibody, NO agglutination reaction will occur.
In short, if the blood typing set-up is what it normally is: drop of blood + ONE type of antibody to a certain, known antigen (e.g."A" antigen, "B" antigen, or "Rh" factor/antigen), then NO agglutination reaction (i.e. NO clumping) observed means that the person DOES NOT have THAT antigen (i.e. the antigen that the antibody is specifically "against", that is, "able to stick to") on the surface of their red blood cells. However, if clumping IS observed, then the person DOES have that antigen present on the surface of their red blood cells.
For your flash cards/study guide:
YES clumping = blood sample HAS the antigen.
NO clumping = blood sample DOES NOT have the antigen
What do I to determine blood type from the 4 blood drops each mixed with a different antibody?
So, determining clumping (agglutination) or not is pretty easy--it's either YES or NO. There is either no in-between in the case of blood typing using antibodies.
IF the blood sample CLUMPS in the presence of "anti-A" antibody, you know the person has the "A" antigen. But that's it, you still don't know if they are type A or type AB blood if you haven't looked at the result for the "anti-B" antibody reaction with their blood. On the other hand, IF the person's blood sample does NOT CLUMP in the presence of "anti-A" antibody, then FOR SURE you can say that the person does NOT have type A blood, NOR do they have AB blood--however, you don't know their definitive blood type yet because they could be EITHER type B or type O. You still need to look at the reaction of their blood in the presence of the "anti-B" antibody. As you can see, you can't blood type using just one type of antibody, you must use all three antibody types used in blood typing: "anti-A" antibody, "anti-B" antibody, and "anti-Rh" antibody.
IF the blood sample clumps in the presence of "anti-B" antibody, then you know the person has the "B" antigen. If you DIDN'T already get the result from the "anti-A" antibody test, then you'll only be able to say that the person's blood is either type B or type AB. If you DID already do the "anti-A" antibody test, and the person's blood HAD CLUMPING in the presence of "anti-A" antibody, then you can determine their ABO blood type (but not the Rh factor--yet, i.e. you can't say whether they are "positive" or "negative" for Rh at this point). For example, if the person's blood CLUMPED in the presence of "anti-A" antibody AND CLUMPED in the presence of "anti-B" antibody (again, these are separate reactions--one never mixes two different kinds of antibodies together for any step of blood typing), then the blood is type AB. However, if there was clumping in the presence of "anti-A" antibody but NO CLUMPING in the presence of "anti-B" antibody, then the blood is type A. The reverse of the last example follows logically: if the blood did NOT clump in the presence of "anti-A" antibody, but DID CLUMP in the presence of "anti-B" antibody, then the person's blood is type B.
What if there is NO clumping in the presence of "anti-A" antibody AND NO CLUMPING in the presence of "anti-B" antibody? Well, then that blood type is type O, because type O blood means the red blood cells have NO antigens, thus there is physically NOTHING for the "anti-A" antibody to stick to, just as there is NOTHING for the "anti-B" antibody to stick to.
I know my ABO type (A, B, AB, or O), but is my blood type A/B/AB/O "positive" or "negative"? This is a question of determining Rh factor.
IF the blood sample CLUMPS in the presence of "anti-Rh" antibody, then the blood is Rh POSITIVE (Rh +).
IF the blood sample does NOT CLUMP in the presence of "anti-Rh" antibody, then the blood is Rh NEGATIVE (Rh -).
When "reporting" one's FULL ABO/Rh blood type, write the ABO blood type (A, B, AB, or O) and then a superscript of either "+" or "-" to indicate either the presence (+) of Rh factor or the absence (-) of Rh factor.
Why is the Rh factor important for medical purposes?
Rh factor is important because of blood transfusions, some organ transplants, and pregnancies in Rh - women.
Rh factor is another type of antigen that determines blood type (overall blood type), and it's important because just like the ABO blood-type matching for blood transfusions, the Rh factor can cause potentially fatal problems for the blood recipient if there is a mismatch. That is, it is a potentially problematic mismatch to transfuse a person with type A (for example) Rh+ (positive) blood to a person with type A Rh- (negative) blood. The problem arises from the fact that the person with Rh - blood may have an immune system that has already made natural, permanent, circulating antibodies to the Rh factor (where Rh "positive" indicates the "presence" of the Rh factor or "antigen" on the surface of red blood cells in that person's blood). In the case of this Rh factor transfusion mismatch, the recipient's "anti-Rh" antibodies would attack the donor's red blood cells due to the presence of the Rh factor/antigen on the surface of the donor red blood cells, which are seen (from the recipient's immune system's perspective) as "foreign", and thus must be flagged for destruction by "anti-Rh" antibodies. This leads to a transfusion reaction in which the recipient's Rh antibodies stick to the just-donated red blood cells the recipient desperately needs, resulting in agglutination and eventual destruction by other immune cells (thus causing "suffocation" at the cellular level through the recipient's progressive loss of oxygen-carrying red blood cells)--if the recipient doesn't FIRST die from the blocking-off of blood vessels all over their body due to the agglutination reaction brought about by the Rh incompatibility in the blood transfusion. On the other hand, it is perfectly safe to transfuse JUST the red blood cells of the a donor with type A Rh - blood into a recipient with type A Rh+ blood. This is safe because the recipient's immune system "doesn't care" if the donor's red blood cells LACK the Rh factor (antigen). Transfusing blood from a donor with type A Rh+ to a recipient with type A Rh+ is safe, of course, BECAUSE the recipient, by virtue of HAVING the Rh factor (antigen) present on their OWN red blood cells, has NO antibodies to Rh factor--thus, there is no possibility of a transfusion reaction based on the Rh factor.
Besides blood transfusions, organ transplants, etc, the other medical implication of Rh factor erythroblastosis fetalis, or the "hemolytic disease of the newborn".
Links:
1. A cute, concise explanation of ABO/Rh blood typing (~15 minute video):
ABO/Rh blood typing explanations easier to process when a proper analogy is used. Here is a link to a great video, that, albeit a bit cheesy, is very appropriate for those who want to learn the fundamentals about ABO/Rh blood typing for the first time.
2. Agglutination of red blood cells by IgM antibodies
3. ABO blood type table
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