Week 4 Flashcards
What does the term Recipient mean in BB terminology?
Individual who receives a transfusion of blood or its
component
What does the term Crossmatch mean in BB terminology?
Mixing of donor RBC’s and recipient sera to determine if invitro reactions may indicate potential for in vivo reaction between donor cells and recipients plasma
What does the term Sensitisation mean in BB terminology?
Attachment of antibody to antigens on red cells
What does the term Agglutination mean in BB terminology?
Cross-linking of antibodies attached to red cells to form visible clumping
What does the term Incompatible mean in BB terminology?
Presence of agglutination or haemolysis in a crossmatch test; these units should not be transfused
What does the term Immediate spin mean in BB terminology?
Mixing donor and recipient blood and reading for
agglutination after the first spin without incubation or enhancement media.
Describe an Indirect Antiglobulin test and when it is normally performed.
Following incubation of donor cells with patient plasma, anti-human globulin reagent is added to detect antibody bound to red cells. Performed when clinically-significant antibodies have been detected in an antibody screen or there is a history of such antibodies.
What is meant by Computer crossmatching?
application of computer software to perform validity checks required for issue of compatible blood
A Crossmatch (CXM or XM) is requested by a doctor when a patient needs, or is likely to need, a blood transfusion what tests are conducted before units of blood are allocated to the patient?
- Consists of the following tests:
- Blood Group
- Antibody Screen
- Crossmatch (computer or full)
A Group and Hold (GPH) is requested by a doctor when a patient may need a transfusion in the future and consists of what tests?
- Consists of the following tests:
- Blood Group
- Antibody Screen
For a group and hold what is the process with blood stock?
• Blood stocks are not reserved for the patient but can be issued quickly should the need arise.
Detection and identification of antibodies against RBC is critical in what 3 situations?
- Pre-transfusion testing
- Investigation of haemolytic transfusion reactions
- Investigating, monitoring or avoiding HDNB
Is the focus of antibody detection methods is on unexpected or expected antibodies?
Unexpected
• Expected antibodies are anti-A, anti-B
The primary importance of antibody detection are ________ _________ produced in response to red blood cell (RBC) stimulation through transfusion,
transplantation, or pregnancy
immune alloantibodies
Naturally occurring antibodies may form as a result of exposure to…….
List some examples
Environmental sources (e.g., pollen, fungus,
and bacteria),
• Their structures are similar to some RBC antigens
• Eg. Anti-Lua, Anti-P1, Anti-I
Passively acquired antibodies are produced in one individual and then transmitted to another via plasma-containing blood components or derivatives such as ____________ . What is another example
intravenous immunoglobulin (IVIg)
• Eg. Maternal antibodies in neonate
• May complicate investigations
Antibodies that cause decreased survival of RBCs are referred to as ___________. They are typically Ig__ and react at _____°C or in the antihuman globulin (AHG) phase of the indirect antiglobulin test (IAT)
Clinically significant antibodies
IgG
37
Which antibodies, when present, can complicate the detection of clinically significant antibodies in pretransfusion setting?
Autoantibodies
They can react with all red cells tested.
What is the name of the guidelines manual that must be followed for antibody screening?
ANZSBT
Australian and New Zealand Society of Blood Transfusion.
What are the 2 types of Antiglobulin Tests performed in the lab? Describe what they are used to detect and give examples of when they are used.
- Direct antiglobulin test (DAT): Used to detect antibody bound to red cells in vivo (within the body) • Eg. Investigations of autoimmune haemolytic anaemia, HDNB, transfusion reaction
- Indirect antiglobulin test (IAT): Used to detect antibody bound to red cells in vitro (in a test tube) • Eg. Antibody screening and identification, crossmatching, phenotyping
- Prepared by injecting rabbits with human antibody molecules (IgG) and complement proteins
- Rabbit’s immune system produces antibodies to human IgG and complement
- Resulting reagent (___) binds to human IgG and complement, whether free in serum or bound to antigens on red cells
Antihuman globulin (AHG) reagent which is used both in IAT and DAT
Describe in detail the process of the DAT
Blood sample from patient, wash RBC’s, mix with antihuman Ab, agglutination =pos
Describe in detail the process of the IAT
Recipients serum + donor blood sample, wash to remove patient serum + anti-human Ig’s. Agglutination =pos
Give some examples of False-Positive results in the anti-human globulin test
refrigerated or clotted specimen Autoagglutinable cells Bacterial contamination of cells Cells with a pos DAT used for IAT Saline contaminated by heavy metals Dirty glassware
Give some example of False-negative results in the anti-human globulin test
Inadequate washing of cells AHG reagent nonreactive AHG reagent not added Serum not added in IAT Inadequate incubation conditions of IAT Cell suspension either too weak or too heavy Low pH of saline Poor reading technique Under or over centrifuged
Antibody Screen: Column Agglutination Technology
• Microtubule filled with a ______ _______ gel.
dextran acrylamide
For an antibody screen CAT what percent suspension is made? Is it incubated or an immediate spin? Do the red cells get washed in the CAT?
0.8% suspension
Incubated @ 37 for 15min
Then centrifuged
No washing step required
What group is used for screening cells and why?
Group O red cells are used to avoid interactions with ABO antibodies. Any incompatibility with the screen cells should be due to antibodies other than normally occurring ABO antibodies.
What are 3 Limitations to antibody screening?
- Antibody titre below the level of sensitivity - Eg. Kidd antibodies are notorious for declining after exposure
- Low-prevalence antigens may not be represented on screening cells
- Lack of homozygous expression of the target antigen on screening cells
- Dosage effects for some antigens
- List 3 factors that Influence sensitivity.
- Cell-to-serum ratio - Prozone (excess antibody) and postzone (excess antigen) causing falsenegative results
- Some methods will vary red cell concentration or quantity of serum
- Temperature and phase of reactivity
- Length of incubation and pH
Which phases suggest more clinically significant antibodies?
Most clinically significant antibodies will react at the AHG phase (and some may react at 37oC as well).
Why would an ‘Antibody panel’ for antibody identification include cells with homozygous expression eg. Rh, Fy, Jk, MNSs ?
To ensure that dosage is being assessed
“Rule-out” technique • Look at red cells that gave _______ reactions in all phases
negative
• Antigens on these cells are unlikely to be the target if there is homozygous expression of the antigen
What is the The 2 and 2 rule?
Test patient serum reacts with at least 2 antigen positive and 2 antigen negative cells
List 4 risks to patient safety regarding transfusion
- Incorrect identification of patient
- Incorrect identity details on sample
- Issuing incorrect product
- Transfusion to wrong patient
Request Forms must contain……
Must contain three identifiers • Full name (both family name and given name or names) • Date of birth • Medical record number And Must contain a declaration:
Request Form
• Should also include
Gender • Date and time of sample collection • Details of test, product required • Clinical diagnosis • Date and time required • Transfusion history • Known antibodies • Obstetric history (Anti-D) • Location • Name and signature of request
Tubes must be labelled with:
- Minimum of two identifiers (three preferred)
- Full name and DOB
- MRN/URNo/IHI if it can be accommodated
- Date and time of collection
- Signature [or initials] of the collector
Request form and sample must carry
identical patient information
Should the phlebotomist handwrite or print up labels?
• Labelling must occur _________
Should handwrite patient details on tube
• Not use pre-printed labels unless from dedicated system
Label immediately after collection in the presence of the patient.
Quality Control for ABO/RhD Typing must be performed at least ______ on every day
pretransfusion testing is performed
once
• Must also be performed when reagent lots change and when the analyser is
started up.
Clinically significant antibodies are generally:
• Those that react in the ______ phase
• Those that react at temperature ______
AHG/IAT
37o
Antibody screen must be capable of detecting ______ at a concentration of 0.1 IU/mL or lower
anti-D
Reagent red cells must come from at least two separate Group ______donors. Why
O
Group O red cells are used to avoid interactions with ABO antibodies. Any incompatibility with the screen cells should be due to antibodies other than normally occurring ABO antibodies.
Reagent antibody screening cells have One cell each of R1R1 R2R2, why R1R1, R2R2?
Strongest expression of all antigens
QC of Antibody Screening Cells
• QC at least once per day with ______ ______
control serum • E.g. weak anti-D • May QC occasionally with additional control sera • E.g. weak anti-Fya , anti-Jka
QC of Antibody Screening Cells Confirms:
- Sensitivity of test procedure
* Integrity of antigens on reagent red cells during storage
Preferred when likelihood of red cell use is minimal
Group and hold
What is performed in a group and hold?
• ABO and Rh(D) group
• Antibody screen
Hold sample for immediate crossmatch if required
Group and Hold validity (time frame:
• _____ from sample collection if it can be confirmed that the patient has not been transfused or pregnant in that time
• _______ from sample collection if patient has been pregnant or transfused in the preceding 3 months
3 months, 72 hours
Panel cells need to have homozygous expressions of
• Jka, Jkb, Fya, Fyb, S and s
• Antibody can usually be confirmed when:
• Reactive with at least two reagent red cells carrying the corresponding antigen
• Non-reactive with two reagent red cells lacking the corresponding antigen
I believe this is the 2 and 2 rule
Ensure that patient cells do not carry the cognate Ag
• If the cognate Ag is present, may indicate __________
an incorrect Ab identification
Phenotyping occurs when :
when Ab is identified
Crossmatch is valid for ____________
lifetime of the sample
Once transfusion commences, crossmatch ______________
ceases to be valid:
• At original expiry date/time of the sample, or
• 72 hours from starting transfusion of first unit
• After a transfusion episode, subsequent samples will have 72 hour
expiry until a gap of 3 months occurs between transfusions
