Blood Bank Flashcards
What are some of the advantages of using an electronic cross match?
- Reduced technical workload
- Less handling of biohazardous material
- Elimination of insignificant false-positive results in the IS
- Improved blood stock management
- Rapid availability of blood
- Ability to issue blood electronically at remote sites
Why isn’t ABO HDFN seen in all babies with an ABO incompatibility and a group O mother?
○ IgG antibodies are usually but not always warm.
○ Density of antigen expression can be lower on foetal red cells
○ A and B antigens are expressed on many non-red cell tissues which can absorb antibody
What are the causes of discrepant reverse grouping?
- Variant of A (A3)
- Recent transfusion with blood group O
- Recent ABO mismatched HSCT
- Fetal maternal haemorrhage
- Loss of antigen
- Neonate (reverse group depends upon what maternal antibodies are present)
- Rouleaux
- Cold reactive auto-antibody
- Non-specific agglutination
- Technical issue
Causes of no reverse group?
• Loss of antibody
○ Recent PLEX
○ Hypogammaglobulinemia
- Neonate
- Technical issue
How do you investigate discrepant reverse grouping?
• If blood group A
○ Test with plant lectin (reacts with A1, not A2)
○ Confirm with genotype (A3)
• If FMH suspected
○ Kleihauer
○ Flow cytometry
• If rouleaux
○ Disperse by suspending in saline
• If cold agglutination
○ Warm sample and perform testing at 37deg
○ +/- DAT, cold agglutination screen
How should ABO and Rh typing be performed when it is being done in the donor/ patient for the for time?
- ABO= forward and reverse group performed twice, preferably by 2 different people
- Rh= twice with 2x different anti-D clones
What is weak D and why is it important?
- Qualitative defect: all epitopes of D antigen expressed on RBCs but are present at a lower density.
○ Some forms of weak D may show a weak or no reaction with D when tested with a direct test at room temperature
○ Therefore most weak D patients will appear as D- when conventional typing methods are used.
• The importance of detecting weak D differs depending upon the population being tested:
○ Not important if patient/ recipient is typed as D- and gets D- blood
○ Is important if a weak D donor is typed as D- and given to D- patients.
○ May result in inappropriate use of RhIg if a weak D positive mother is typed as RhD- (Weak D subtypes other than 1, 2 and 3 should still receive RhIg).
○All D- donors screened for weak D.
What is partial D and why is type VI the most important type of partial D?
Quantitative defect: absence of a portion or portions of the total material that comprises the D antigen
DVI variant is the most immunogenic of the D variants.
Important to determine if the reagent you are using to type D is sensitive or insensitive to DVI
- Donors with DVI should be typed as D+, sensitive reagent used
- Patients with DVI should be typed as D-, insensitive reagent used
- Pregnant patients with DVI should be typed as D-, insensitive reagent used
- Neonates with DVI should be typed as D+, sensitive reagent used.
With respect to the Rh antigens, what are compound genes and what are two examples?
- Epitopes which occur due to the presence of two Rh genes on the same chromosome (i.e in a cis position)
- ce in cis (i.e. dce)= forms the antigens c, e and f (which is c+e)
- Ce in cis (i.e. DCe)= forms the antigen C, e and Ce (Rh1))
What additional tests should you do when someone has an anti-E antibody on serological testing?
R1R1 who make anti-E frequently make anti-c
○ Patients with anti-E should be phenotyped for c antigen
○ If patients appear to be R1R1, should be transfused with R1R1 blood
○ Anti-c frequently falls below detectable levels.
(anti D and anti C, anti D and anti G, anti c and anti f also commonly occur together)
Which blood group antigens are enhanced, unaffected and reduced by enzyme treatment?
Enhanced
- ABO/H
- Rh
- Kidd
- Lewis
- I
Unaffected
- K
Reduced
- Duffy
- MNS
What are the causes of a pan reactive panel with varying reaction strengths seen?
Autoantibody showing a degree of specificity
Autoantibody + alloantibody
Single alloantibody that shows dosage
Multiple alloantibodies
What are the Chido Rodgers antigens and how is the neutralisation test performed?
- Not true blood group antigens: located on C4b which gets absorbed onto the RBC surface
- Rg found in >98% of population
- Anti-Rg= IgG and detected with IAT but does not cause HFDN or transfusion reactions
- Neutralisation test:
1) Equal vol patient plasma and pooled normal plasma (normal plasma contains Rg antigen and will neutralises any antibody present)
2) Neutralised plasma tested against panel of red cells where reactivity was seen
3) Control (using 6% alb in place normal plasma) must remain positive while the neutralised plasma will be negative
In what situations can a positive DAT be seen?
○ Transfusion reaction ○ Immune mediated haemolysis ○ HFDN ○ Passive acquisition of alloantibodies (i.e. The foetus/ neonate, post IVIG) ○ Post ABO incompatible solid organ or HSCT transplantation (DAT produced by donor/ passenger lymphocytes) ○ Autoimmune conditions- SLE ○ Hypergammaglobulinemia ○ Hospitalised/ unwell patients ○ Healthy donors
How can red cell phenotyping be performed on cells with a positive DAT?
Use monoclonal IgM reagents
○ Such reagents not available for Fya, Fyb
For the Duffy antibodies and where the control column is positive with monoclonal reagents:
○ EGA treatment (will destroy Kell but not the other clinically significant antigens)
When is an elution performed?
- To identify autoantibodies coating red cells in vivo.
- To identify causative alloantibodies in cases of transfusion reaction.
- To identify maternal antibodies coating baby’s red cells in HDFN.
- To isolate specific antibodies from plasma containing multiple antibodies, by absorbing antibodies from the plasma onto selected red cells in vitro and performing an elution.
What are some of the causes of a non-reactive eluate?
- Antibody to an antigen not represented on the test cells
- Anti-A or Anti-B antibodies present and test performed on standard, group O cells (HDFN, post transplant, post IVIG or transfusion of ABO mismatched plasma or platelets)
- Antibody directed against drug or drug metabolite rather than a red cell antigen.
- Autoimmune process may cause non-specific binding to the red cell
- No IgG on red cells- complement only
- Antibody recombined with antigen before the eluate was separated from the cells.
- Inadequate washing
- Old sample.
