Week 5 - Antibody detection Flashcards
CONDITIONS THAT AFFECT ABO/RH TESTING
Antigen Problems:
1) Genetic Mutations resulting in abnormal antigens (Weak D)
2) Disease states resulting in changes to antigens (abnormal or lack the antigen)
3) Antisera that cross-react with other antigens
-affects lab testing (CAD, warm AUAB)
-can affect pt - if they dont have a blood group or AB it can delay getting blood ready them
-in emergency situation you can give uncross matched blood
CONDITIONS THAT AFFECT ABO/RH TESTING
Polyagglutination:
-red cells are agglutinated by all human sera.
-due to exposure to a normal “hidden antigen” or a red cell antigen mutation.
-If you test these cells with human antisera, they will show agglutination regardless of the antibody specificity
-Patients will be grouped as A and B Rh-positive even if they do NOT have
those antigens
-Acquired T activation is caused by a bacterial or viral infection (seen in
children diagnosed with Streptococcus Pneumoniae)
What are ALLO ANTIBODIES (NON SELF ANTIGENS)
- Produced as a normal immune response
- Patient’s history of previous transfusions and pregnancies is
essential in antibody investigations. - Patient diagnosis is vital information (Sickle cell patients are
more likely to produce Antibodies).
What are AUTO ANTIBODIES
-formed when body doesnt recognize self
–These antibodies react with almost all human red cells; they are usually
non-specific or specific to a very high incidence antigen (Anti-e).
-Cold Autoantibodies –IgM and react at RT or 4˚C
-Warm Autoantibodies- IgG and react at body temperature
-Autoantibody can be detected in the patient’s plasma and attaches to the patient’s own red cells
-Antibodies attached to the red cells in vivo can be detected with the Direct Antiglobulin Test (DAT)
-difference between DAT and IAT is the incubation period, IAT needs the incubation to join AB to AG
ANTIBODY DETECTION
-detects antibodies in the patient’s plasma- Reverse grouping , they are naturally occurring (RA/RB reagents)
-if positive then AB are present
-Rh antibodies are Red Cell Immune
-OBG antibodies are Red Cell Immune and depend on the production and stimulation of IgG or IgM forms
-Rh and OBG antibodies are not expected to be present in the patient’s plasma if they are then its from exposure to RBC from transfusion or pregnancy
STIMULATION PROCESS
-first exposure, you may or may not develop an antibody
1-Antigens on Red Cells are introduced to the Recipient.
2-Patient Lacks the Antigen. The immune System recognizes
antigens as Foreign.
3-Antibody Production
IgM or IgG
4-Memory Cell, Secondary Response, and Antibody levels react faster.
5- Significant Antibodies destroy red cells.
Antibody production depends on:
- Immunogenicity of the antigen: The ability of the antigen to elicit an
immune response or to stimulate the production of antibodies. - Rh and Kell are most immunogenic
- Immune system of the individual
- Protocol is to test all patients who have the potential to be transfused and pregnant
ABO AND RH TESTING
All pts are tested with
1) Anti-A
2) Anti-B
3) Anti-A,B (Michener)
4) Anti-D1/D2
5) Reverse ABO performed on all patients > 4 months of age
6) Weak D performed on Rh-negative babies with Rh-negative moms, and donor testing (at CBS)
7) Rh Control not routinely done (Discrepancy on D1/D2, AB Rh positive patients, and Weak D testing)
8) In the Hospital, no reverse testing and only confirmation testing is performed on donor units
- Rh Control added to all patients who initially type as AB Rh positive
- Need to rule out spontaneously agglutinating cells
TESTS TO DETECT ANTIBODIES
***
all testing is based on AB-AG reactions
-reaction is either agglutination or sensitization
-one is known and other is unknown
SCREENING CELLS
-commercially prepped
-2 or 3 cell suspensions
-each row is a different donor
-Group O cells are chosen to prevent a reaction with the patient’s Anti-A,
Anti-B, and Anti-A,B (ABO antibodies).
-each cell is phenotyped with results on the antigram
-+/0 is the presence or absence of AG
-needs pos RBC for all blood type
-should be able to detect all ABs
-homo is prefered because it is the strongest AG expression to detect weak ABs for dosage
- (Duffy/MNSs) Destroyed by enzymes
-known part of reaction is AG in panels
-lot number and exp date are specific to the set of cells used
-antigrams give you an AG profile
SCREENING CELLS
phenotype for cell 1 and 2
11.Rh Phenotype Cell 1 is always R1R1 and cell 2 is always R2R2.
12. This provides a homozygous cell for each Rh antigen (C, E, c, and e).
13.Antibodies to C, E and c are common.
SCREENING CELLS
what do we prefer for OBG AG
For OBG Antigens we prefer to have Homozygous expression, but this is
not always possible.
What happens if person for AB screen has weak Anti-Jkb
-may not detect
-example of dosage in which the heterozygous Jk(a+b+) cell has too few Jkb antigens to demonstrate agglutination.
SCREENING TESTS
Three methods for Antibody Screen:
1)Tube Method - (iat) - detects cold AB
2)Micro Typing System or MTS (Gel column method) -no washing or CCC
3)Solid Phase Red Cell Adherence (Capture R)
donor cell is tested with the patient’s plasma - unknown Abs
All 3 use the same concept of screening cells, but the red cell suspensions differ.
Antigrams are used in all 3 methods.
The purpose of ALL 3 methods is to pick up any significant antibodies in the patient’s plasma
SCREEN RESULTS
-No guarantee that the antibody is NOT present
-AB can be weak and can be undetected
-Weak Antibodies mean fewer IgG Once exposed a second time, the immune system is stimulated and produces more antibodies.
-This is the one LIMITATION in pretransfusion testing.
-May not be able to detect antibodies unless restimulated after being transfused.
-different methods detect different AB
-Tube is IS = IgM is detected
-MTS and Capture R have AHG phase, warm and IgG AB (can miss cold AB like M and N clinically insignificant)
-screening wont pick up rare AB
