Chapter 6 Flashcards
Hemagglutination ocurrs in 2 ways
Sensitization
Hemolysis
What is sensitization?
When antibodies attch to the antigens on RBCs and visibly agglutinates
What causes hemolysis?
Complement activation which results in the breakdown of the cell membrane
The antiglobulin test depends on 2 basic principles
Antibodies are globulins
The antihuman antibodies bind to the Fc portion of the sensitizing antibodies and form bridges between antibody-coated red cells, resulting in visible agglutination
The indirect antiglobulin test (IAT) was first used to
detect IgG anti-D
What factors affect the Indirect Antiglobulin Test?
Incubation time and temperature pH (6.8-7.2) Ionic concentration (LISS) Affinity constant of antibody Proportion of antigen to antibody
What are the application of the indirect antiglobulin test?
Unexpected antibody detection Unexpected antibody identification Antibody tiration Red cell eluate testing Cross match Cell typing
The FDA requires screening be performed with group O cells with the following antigens
D, C, c, E, e, K, k, M, N, S, s, P1
Jka, Jkb, Fya, Fyb, Lea, Leb
Compatibility testing encompasses
ABO/Rh
Antibody Screen
Crossmatch
The antibody screen is used to
detect antibodies in the patient that are directed toward common or high prevelance antigens (will not detect low frequency antigens)
Autocontrol is
Mixing the paitents RBCs with the patients plasma to detect antibodies bound to the patients own RBCs
What are some issue that would cause a positive crossmatch but a negative antibody screen?
Incorrect ABO selected for crossmatch
Donor cells are subgroup of A or B ( which was incorrectly labeled as O)
Passive transfusion of ABO antibodies (A patient recieves O platelets)
Crossmatch contained low incidence antigens
Screening cells are single dose, crossmatch cells are double dose
Age of screen cells vs. fresh donor units
What percent of labs use gel technology?
45%
Why do most labs not perform IS or room temperature incubation?
To avoid cold reacting antibodies
Transfusion history is critical pre-analytical information. Between autoadsorption and alloadsorption, which one must be used for recently transfused patients?
Alloadsorption must be used for recently transfused patients.
What is an autoantibody?
An antibody produced by the immune system that is directed against one or more of the individuals own proteins.
What is an alloantibody?
An antibody formed in response to pregnancy or transfusion targeted against an antigen that is NOT present on the person’s RBCs (targeted against non-self red cell antigens)
To identify an antibody you must perfrom
DAT
Rh Phenotype (If Rh antibody suspected)
Initial Panel
Any follow-up selected cells
Antibody screening panel cells are always from this group
Group O
What is Direct Agglutination?
IgM
Binding to more than one red cell antigen at a time, bridging the cells together to form a clump
What is Indirect Agglutination
IgG
Sensitized RBCs are coated with antibody, but they can’t bridge the gap between cells. Add AHG reagent to detect coating of cells. (Coombs 1945)
A mix field specimen will conatin
2 cell populations (patients cells and donor’s transfused cells)
The sample used for pretransfusion testing must be under _____ old
3 days old
Many antibody panels will be positive for these high incidence antigens
Jsb, Kpb, Jra, Lub, Ata
Selected cells are used too
rule out antibodies on panels that have several antibody possibilities
One you determine the antibodies on the antibody screen you must
type the patients cells for antigens (as long as they have not been recently transfused)
If a patient has multiple antibodies to high frequency antigens, you may need to
get blood from the American Rare Donor Program
Enhancement media is used to
strengthen the antibody-antigen reactions
What is the simplest form of enhancement>
increase the serum to cell ration
3 drops serum to 1 drop of cells
What are the benefits and drawbacks of albumin as enhancement media?
Enhances Rh antibodies
Brings in nuisance antibodies
Requires 30 minute incubation
Rarely Used
What are the benefits and drawbacks of PEG as enhancement media?
Enhance Kidd and Duffy antibodies
Brings in warm autoantibodies
Which antigens are destroyed by enzymes?
Duffy MaNuScript Duffy MNS(s)
What are the proteolytic enzymes?
Ficin
Papain
Trypsin
Bromelin
What are the 2 sulfhydryl reagents and what is their purpose?
STT and 2-ME
Cleaves disulfide bonds on IgM, making it unable to bind to antigens (used to rule out IgM)
Also affects k, Kpb, Jsb, LW, Yta
Ficin is used to
Remove Duffy MNS(s) antigens
Removes these antigens to find other “masked” antibodies present in backgrouns
DTT is used to
destroy Kell, LW, and Scianna antigens
Can be used as a selected cell
What kind of antibodies are insignificant. Examples
Some antibodies which are only cold reactive
Anti-Leb, Anti-P1, Anti-M, Anti-N, Anti-A1
Any antibody reacting at 37 degrees is
clinically significant
Antibodies not reactive at the AHG phase my be
clinially insignificant
This percent of hospital patients has a positive DAT
1-15% (much higher then the general population)
The DAT procedure refects the in ___ reactions of patients
in vivo (in the body)
What is the purpose of the DAT test
to check to see if red blood cells are coated with complement and /or antibodies in vivo (in the body)
DAT procedure
Take a sample of RBCs, wash them to get rid of unbound antibody and complement, add AHG, centrifuge, look for agglutination.
Positive may mean: delayed HTR, autoantibodies, HDNF
About 13% of poditive DAT tests are sue to
C3d
What is eveidence of decreased red cell survival?
Increased retics Elevated bilirubin Decreased Hct with no evidence of bleeding Positive DAT prescence is significant
A positive autocontrol my be a sign of
Delayed Hemolytic Transfusion Reaction
DAT is probably positive too
When a positive DAT is a mixed field it is because
The transfused cells are coated, but the patients cells are not
What is an elution test?
A test which strips antibodies from cells. An antibodie screen can be run on an eluate.
A Last Wash Control ensures
Antibodies came off of RBCs and were not from serum or plasma
What is a warm autoantibody?
Antibodies to antigens on a patients RBCs that react at body temperature
What is AIHI?
Autoimmune Hemolytic Anemia
This test will almost always be positive in patients with Autoimmune Hemolytic Anemia (AIHI)
DAT (90% of patients)
In 50-90% of patients with AIHI, this will be found in their serum
autoantibodies
_____ must be excluded by adsorption/elution procedures because they mask _______.
Alloantibodies must be excluded because they mask autoantibodies
When autoantibodies are adsorbed onto RBCs this must be used as enhancement
ZZAP
Low incidence atingens %
1%
High incidence antigen %
90%
Fy(a-b-) is nonexistant in this race, but exists in
Fy(a-b-) not in Caucasians
Present in African Americans
How do newborns get antibodies?
From mom throught the placenta
How do you test a baby for HDNF?
Test for anti-ABO, Anti-D, or other antibodies
Run an eluate of positive DAT cells to determine what is coating baby’s cells
If it is an alloantibody, you can detect it in serum or plasma
A patient can have passively aquired antibodies (such as anti-A and anti-B) if they were transfused
with non-ABO identical plasma
