BB - Day 4-5 Flashcards
What could be a reason why we get a positive auto-control as it relates to IgM autoantibodies? How can we avoid getting a positive AC?
IgM autoantibodies cause complement to bind to cells. C3 interferes with AHG testing and gives us a positive AC
Use monospecific AHG
- contains anti-IgG
- polyspecific AHG contains anti-IgG and anti-C3
If we suspect IgM antibody in the patient’s plasma, what test can we do to confirm?
At 4C, agglutination reactions should be stronger compared to room temperature
If we suspect IgM antibody in the patient’s plasma causing agglutination after 37C or AHG, how can we resolve this issue?
Pre-warm screen: warm everything to 37C and do whole test at 37C. Avoid letting reagents or cells cool down
After an antibody ID, we can type the patient’s and donor’s cells for the antigens corresponding to the antibodies identified. The cells should be ___ for these antigens
Negative
- have antibody in patient serum, so must be negative for the antigen
- donor cells must not have the antigen as well for transfusion to proceed
Bandeiraea simplicifolia is a lectin that targets…
B cells (anti-B lectin)
The major crossmatch test consists of mixing these two components
Patient’s serum
Donor RBCs
The minor crossmatch test consists of mixing these two components
Donor’s plasma
Patient’s RBCs
Explain why an antibody screen would be positive and a crossmatch negative. Can we proceed with the transfusion?
An unknown antibody in the patient’s plasma reacted with an antigen on the screen cells
Cannot proceed with transfusion until the antibody(s) is identified, and phenotyping shows the donor is negative for the corresponding antigen
What test should we run if the antibody screen is negative but the crossmatch is positive?
DAT on donor cells
-positive DAT indicates cells are sensitized and AHG phase of the crossmatch will be positive
What is phenotyping? What antigens does phenotyping look for?
Testing cell with known antibodies to determine antigens
-same as forward typing
Antigens other than A, B or D
When phenotyping, what does the negative control cell ensure?
No false negative reaction and specificity of the anti-serum
When choosing a positive control cell for phenotyping, the antigen should be hetero or homozygous for the antigen? Why?
Heterozygous
Ensures antibodies in serum are strong enough to react with a weak/heterozygous antigen
-gives confidence in the results
After an antibody has been identified in the patient’s serum, when we perform phenotyping on the patient’s RBCs, the target antigen should be…
Absent (negative result)
-patients should not make antibodies against their own antigens
Phenotyping uses either DAT or IAT. The difference between the two tests is that DAT are class ___ antibodies while IAT are class ___ antibodies.
IgM = incubate at room temperature
-mostly Rh group. Note: Rh antibodies mostly IgG in nature, but commercial anti-sera uses IgM
IgG = incubate at 37C for 15 mins, add AHG
What is an antibody screen used to look for? What is the term for these antibodies?
Detect RBC antibodies other than the “expected” anti-A and anti-B
- anti-A and anti-B are naturally occurring IgM
- screen looks for “unexpected” antibodies
Alloantibodies
Is the antibody screen a DAT or IAT test?
IAT - patient’s serum + screen cells
What types of cells does the antibody screen test use? Why?
O cells
No A or B antigens expressed on O cells to bind to anti-A or anti-B, so will not interfere with detection of unexpected antibodies
Antibody screen - are the antigens expressed on the red cells homozygous or heterozygous? Why?
Homozygous
Double dose of the antigen so if patient’s serum has alloantibodies, they are more likely to bind to the screen cells
What do enhancement reagents promote? How?
Antigen-antibody binding/agglutination by reducing the zeta potential
What do auto-controls check for? What does it consist of?
To see if patient’s serum may agglutinate own cells (autoantibodies)
Consists of patient’s cells and serum
Enhancement solution is used for these tests… What is the exact enhancement solution called? What tubes is the enhancement solution added to?
Antibody screen and antibody panel
LISS
SI, SII, SIII, AC
The difference between the antigens used in screen cells and antigens used in the positive control for phenotyping is…
Screen cells are homozygous for the antigen
Phenotyping positive control cells are heterozygous for the antigen
3 most common enhancement reagents include…
LISS
PEG
Bovine albumin
A DAT positive test indicates this tube is also positive…
Auto-control
Antibody panels are done when one of these two tests are positive
Antibody screen (ABS)
DAT
If the DAT is positive, we must perform an antibody panel. However, we must first perform a…
Elution
Why would we want to do an antibody screen before an antibody identification panel?
Antibody ID panels are long, cumbersome and expensive. If our initial screening cells are negative and there is no agglutination for the cross-match, then there is no reason to do an antibody panel
When identifying antibodies, what rules do we follow to “rule-in” an antibody?
Rule of 3: at least 3 cells positive and 3 cells negative for the antigen. Positive cells should show a positive test reaction at one of the readings.
Cells positive for the antigen should show a positive test reaction while being negative for other possible antigens.
When identifying antibodies, what rules do we follow to “rule-out” an antibody?
Homozygous crossout - one is enough
Heterozygous crossout - 2 or more heterozygous crossouts required if antibody is clinically significant (anti-K), or 1 heterozygous crossout if antibody is clinically insignificant (anti-M, anti-N) or low incidence (anti-Kpa, anti-Jsa)
The titer interpretation is observed in the tube that is the ___ dilution that produces a ___ grade macroscopically
Highest
1+
- with AHG
- titer is the reciprocal of the dilution
