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Positive DAT and Immune Destruction
Terms in this set (42)
How does an autoantibody differ from an alloantibody?
An autoantibody is an antibody to self (auto-anti-e in e+ person); alloantibody is developed when antigen is presented through transfusion or pregnancy (anti-K in a K- person)
Does autoimmunity always cause anemia?
No, only when destruction of RBCs exceced body's capacity to produce new RBCs
Which is the most common kind of autoimmunity?
What is the least common kind of autoimmunity?
Paroxymal Cold Hemagglutination (PCH).
What is the mixed type autoimmunity?
Warm and Cold serological features
What is the major cause of autoimmunity?
What is the secondary cause of autoimmunity?
Diseases states like lymphomas, MM, CLL, Lupus, viral disease & pneumonia
Which type of hemolysis is the most common, intravascular or extravascular?
What type of immunoglobulin is associated with intravascular hemolysis?
IgG1 & 3 and IgM (fix complement).
What laboratory test can help distinguish between an allo and an auto antibody?
DAT or autocontrol. (+) DAT and autocontrol is for autoantibody; (-) DAT and auto control is for alloantibody
If the patient has been recently transfused, what makes it difficult to determine if the antibody is allo or auto?
autoantibodies attach to antigen on RBCs, alloantibodies attach to transfused RBCs, both giving (+) DAT beit transfusion rxn, drug-induced, or passively transfused alloantibody. It response is anamnestic, the antibody screen will be negative until titer is high enough to "spill over" into plasma.
What is major clinical sign of an autoantibody?
evidence of RBC destruction by an antibody
What would you look for on a blood smear if you're looking for hemolysis?
Polychromasia, spherocytes, and fragmented cells.
What lab values would give you evidence of hemolysis?
dec. haptoglobin, inc. LD, inc. plasma Hgb and bilirubin.
Will autoantibodies generally cause you problems with the ABO/Rh grouping?
Not warm autoimmune antibodies (react @ 37C & ABO is RT); Cold autoantibodies will because they react @ RT.
Is the antibody screen always positive with an autoantibody?
No. excess antibody must be present coating all cells and spilling over into the plasma
List 5 reasons for a positive DAT.
Autoantibodies, transfusion rxns, alloantibodies passively transfused to recipient (ABO), HDFN, and drug induced antibodies
What tube is preferred for drawing blood for a DAT and why?
EDTA; it ensures sensitization in vivo. Red tops has sensitization in vitro.
Which is more common on the red cell with a warm autoantibody, IgG and/or complement?
IgG and C' @ 67%; 20% are just IgG and 13% is just C'.
What is an elution and how is it related to an eluate?
The antibody is removed from RBC chemically or physically and goes into a solution which is the end product (eluate).
How can you determine what antibody is in the eluate?
Test against antibody screening cells. if positive, run panel to Id antibody.
Why do you only read the eluate panel at AHG?
IgG is removed in elution procedure which is only detected @ AHG once incubated @ 37C, washed, and AHG is added.
What is an adsorption?
Removing antibodies from serum by placing antigen (+) RBC in serum and allowing antibodies to attach. It can confirm presents of antigen (antibody on RBC confirmed by elution) or remove antibody masking other antibody for detection.
How does an autoadsorption differ from an alloadsorption?
auto adsorption uses persons own RBCs to adsorb out autoantibody in own person's plasma; alloadsorption uses someone else's RBCs to absorb antibodies out of other person's plasma.
If a patient's cells are already coated with autoantibody, how are you going to get more autoantibody to adsorb onto the cells and be removed from the plasma?
Use chemical or heat to remove autoantibodies from RBC then use enzymes to enhance adsorption of more autoantibodies. Wash after treatment
How does ZZAP work?
In one step, IgG autoantibody is removed and cells are enzyme treated. Can use chloroquine but that requires two steps.
Why should you NOT autoadsorb a person's serum if they have been recently transfused?
Clinically significant alloantibody can be adsorbed out.
What is an allogenic adsorption?
Using other RBCs w/different antigens it removes alloantibodies that where hidden under autoantibody rxns.
What is the most common warm auto-antibody?
What is the second most common form of autoimmunity?
Cold agglutinin syndrome or cold hemaglutinin disease
How do you adsorb out a cold autoantibody?
If not recently transfused, wash the cells with warm salin and pretreat w/ZZAP. Mix patient's cells w/own serum and incubate @ 1-6C; if recently transfused use RESt (I-rich).
What is the most common cold auto-antibody?
How does PCH antibody work?
The biphasic IgG fixes C' when blood cools in body limbs and lyses cells when body is warmed
Why do you frequently get a negative antibody screen when the patient has an antibody to a drug?
Drug isn't present in I, II, III screen cells. If add to screen cells, a positive rxns will happen when serum is added.
What is the most common specificity of the PCH auto-antibody?
Anti-P (Donath-Landsteiner antibody)
What is the treatment for a drug induced AIHA?
Switch patient to another drug
What type of immunoglobulin is associated with extravascular hemolysis?
How does autoantibodies cause a (+) DAT?
they react w/recipients own RBC antigens.
How do transfusion rxns cause (+) DAT?
recipeient develop antibodies to antigens on transfused cells.
How do passively transfused antibodies cause (+) DAT?
In the donor plasma seen most often w/ABO antibodies from a platelet transfusion.
How does a baby w/HDFN cause (+) DAT?
Maternal IgG cross the placenta attaching to fetal cells and causing a (+) DAT on fetus.
How does drug-induced antibodies cause (+) DAT?
The drug binds to RBC membrane, then the antibody attaches to it on the RBC.
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