Pre-Transfusion Testing Flashcards
What is the principle of the Antiglobulin test? What is this also known as?
Based on the principle that AHGs from immunized nonhuman species bind to human Immunoglobulins like IgGs or complement either free, in serum, or attached antigens on RBCs. This test is also known as Coomb’s Test.
Discovery of AHG lead to the finding of what blood group systems?
- Duffy
- Kell
- Kidd
What are the two classes of AHG sera?
- Polyspecific
- Monospecific
What is the difference between monospecific and polyspecific AHG production?
- Monospecific - Hybrodoma technology; fuses murine spleen lymphocytes with myeloma cells to create immortal cell line. this make a specific antibody directed at a single epitope
Polyspecific- inject animals with human globulin components and collecting the antihuman antibodies. more than one spleen lymphocyte wille produce immunoglobulins. Sera directed at multiple epitopes.
What is contained in Rabbit Polyclonal?
What part of the immunoglobulin chain is it specific to?
What is contained in Monoclonal IgG?
- Contains anti-IgG with no complement activity through hybridoma technology.
- IgG heavy chain
- Murine Anti-IgG
All of the following are advantages of Monoclonal AHG except?
- Higher titre of Ab than polyclonal AHG
- No batch variation
- Not subject to cross reactivity
- Over-specificity
- Over- specificity (disadvantage)
What are some disadvantages of Monoclonal AHG?
- Over-specific
- only one epitope
- may need to blend serval monoclonal antibodies to ensure variants detected
- overly sensitive
- complement fixation may not start
What are the advantages of Polyclonal AHG?
More likely to pick up variants
cheaper
What are the disadvantages of Polyclonal AHG?
Low specificity
Low titre
What is contained in the following?
- Rabbit Polyclonal
- Rabbit/murine polyclonal blend
- Murine monoclonal
- anti-IgG and anti-C3d
- blend of antihuman IgG and murine monoclonal anti-C3b and anti-C3d
- Murine monoclonal anti-IgG, anti-C3b and anti-C3d
What class of antibodies make up a majority of the mixture in AHG?
IgG1 and IgG3 subclasses
Although rare, why might IgM antibodies be found in AHG?
Can fix complement so detected by anti-complement
What is the principle of IAT?
-
Detect in-vitro sensitized cells. This is a two stage process.
- Cells (antigens) exposed to antobodies via antisera / serum
- antobodies or complement sensitize RBC during invitro incubation phase; 37C in LISS/albumin
- Cells tested with AHG to check for sensitization and strenght of reation is graded
What is the principle of DAT?
- Detect in-vivo sensitized red cells with IgG and/or complement components.
- RBCs mixed with AHG to determine if sensitization has occurred.
Identify some of the causes of in-vivo antobody-antigen complexes? (4)
- AIHA
- HDN
- Drug-induced hemolytic anemia
- HTRs
When might a DAT be required?
- If patient has benn transfused over the last 2 weeks
- has a history of antibodies
- is pregnant
Why does the DAT not require an incubation phase?
Because the antigen-antobody complexes have occured in-vivo.
How are positive DAT results monitored?
DAT panel usisng monospecific anti-IgG and anti-C3d to determine the specific type of protein sensitizing the cell
Interpreting the significance of a postive DAT requires?
- Knowlege of patient’s diagnosis
- drug therapy
- recent transfusion therapy
- all of the above
All of the above
DAT can detect what level of IgG and C3d molecules per RBC?
- IgG = 100 - 500
- C3d = 400 - 1100
IAT can detect what level of IgG and C3d molecules per RBC?
- IgG and C3d = 100 - 200
What factors influence IgG molecules sensitized on RBC and rate of sensitization?
- Serum : cell ratio
- Reaction medium: Albumin, LISS, PEG
- Temp.
- Incubation time
- Washing RBCs
- Saline used for washing
- Addition of AHG
- Centrifugation for reading
What can cause false positives with the AHG test? (6)
- Bacterial contamination causeing T antigen activation (caused agglutination)
- Saline/glassware contamination
- Extreme reticulocytosis
- AHG contaminated with Rabbit-transferrin
- Positive DAT cells cannot be used in IAT as test would always be positive
- refridgerated specimens - cold auto abs sensitize cells
What can cause false negatives?
- Anticoagulated plasma / old serum
- poor washing can neutralize AHG
- Contamination with human globulins
- Elution of Ab during washing
- incorrect incubation temp.
- cell:serm ratio
- undercentrifucation
- Forgetting to put in AHG
Who is antigen typing performed on?
Patients with a history of clinically significant antobodies
Blood untis for this group for transfusion should be?
Antigen negative to clinically significant antibodies.
How are the number of units to be transfused calculated for Antigen typing?
The number of units requested is divided by the frequency of the antigen-negative individuals.
- Example: Crossmatch request for 2 untis of RBCs for a patient anti-E positive.
- 2 units/ 0.7 (freq. of E -ve people) = 2.8 (3 units must be typed to find 2 E -ve units)
- If multiple abs; E-ve and c-ve
- 2/(0.7x0.20) = 14.3 (14/15 units tested to find 2 units E and c -ve)
Why is knowing the donor’s race useful?
Antigen incidence varies between races
For whole blood transfusions - when antibody(ies) are identified the patient’s red cells should be phenotyped for corresponding antigen gto confirm the validity of the test results.
Patient should lack the antigen with the following exceptions?
- Autoantobody and there is a positive DAT
- Antigen present of previosly transfused cells
- For red cell transfusion Donor cells should lack corresponding antigen to patient’s abs.
What factors are valuable in the abs identification process?
Why is knowing if a patient has been previosly transfused or pregnant important?
- Pt hx
- age
- sex
- race
- diagnosis
- transfusion history
- pregnancy
*transfused or prego Pts may have created an ab as they were exposed to non-self antigens.
What is the best approach for narrowing down you antobodies(y) possibilities on an Ab ID panel?
- Exclusion method
- based on negative results obtained against a panel of 11-20 manufactured O cells, in all 3 phases of testing using homozygous expressed antigens.
- If antigen present on panel cell and patient’s serum did not react it can be ruled out.
How is the inclusion method carried out?
After negative cells evaluated, remining positive antigens examines to see if pattern of reactivity mathces a pattern of antigen positive cells.
- If multiple abs are present how might you seperate specificities and enable idetification?
- How does this affect the RBC membranes?
- What is the purpose of doing this?
- Treat panel cells with enzymes
- modify RBC surface by removing salic-acid residues and denaturing or removing glycoproteins.
- To enhance expression of certain antigens and destroy others.
If the Ab panel does not ID one specific Ab, what may be done?
Additional panels cells tested to veriry or ID multiple Abs. Ensure selected cells have minimal overlap.
When might selected cell panels also be useful?
Selected cell panels also useful when patient has a known Ab and technologist is trying to dermine if additional Abs present.
Describe the principle of Adsorbtion?
- Antibodies removed from serum by addiung target antigen and letting antobody bind to antigen.
- Solid precipitate formed (antibody-antigen complex)
- removed by centrifuge
In adsorbtion the adsorbent is typically composed of?
RBCs
What is the adsorbed serum tested against and for what?
RBC panel for unabsorbed alloAbs
What Commericial Reagents are available for adsorbtion?
- Human Platelet concentrate
- Rabbit Erythrocyte Stroma (RESt)
What is Human Platelet concentrate used to adsorb?
How does this happen?
- Bg-like antibodies from serum
- HLA antigens on PLTs bind the HLA related bg-like Abs, leaving oth. specificities in serum.
- Antibody ID performed on adsorbed serum
RESt is used to adsorb what Abs?
What structures does RESt have?
How does RESt adsorbtion carried out?
- Some cold reacting Abs.
- H, I and IH-like structures
- Incubate at 4oC will remove insignificant Abs, which may interfere w/ significant warm-reating Abs
Most oth. Ab specificities remain unaffected by by RESt, however, RESt possesses what kind of structures?
The structure similarity means RESt adsorbed serum should NOT be?
- Similar to B and P1 antigens
- RESt ,may adsorb anti-B
- NOT used for Reverse grouping and crossmatching
What antibodies are commonly removed via Autoadsorbtion?
Autoabs
What does the simplest method of autoadsorbtion use to remove abs?
Patients own RBCs
What is the FIRST STEP in autoadsorbtion?
Wash patient cells to remove unabound Ab
What is the second step in autoadsorbtion?
May treat cells to remove any autoAb coating cells
What is the THIRD step in autoadsorbtion? How long?
What does the temp depend on?
- Incubate patient cells w/ patient serum for up to ONE HOUR
- thermal range of autoab being removed
What is the FOURTH step in autoadsorbtion?
Look for agglutination in sample (+ve agglutination = RBC binding sites saturated with autoAb)
What is the FIFTH step in autoadsorbtion?
What happens if not agglutination present?
Harvest serum and incubate with new aliquot of autologous cells.
- Harvested serum tested against patient’s RBCs, if no reaction happens adsorbtion is complete.
- If reactivity happens = further adsorbtion needed
How many aliquots are needed for autoadsorbtion to occur?
3 - 6 aliquots
Describe when homologous adsorbtion may be used?
- Patient seveerly anemic so not enouch autologous RBCs for adequate adsorbtions.
- Patient recently transfused; donor RBCs may adsorb alloAbs
How is homologous adsorbtion carried out?
- Patient phenotyped
- RBCs matched to phenotype and used for adsorbtion in place of autologous cells
In homologous adsorbtion, if an exact match cannot be made what is the focus?
Finding cells that lack antigens to which patient may form alloAbs
When might Differential Adsorbtion be used?
Phenotyping patient is Hard because of DAT or recent transfusion.
Describe the method of Differential Adsorbtion?
Patient serum split into 3 aliquots
Eacg aliquot adsorbed using a different cell
What cells are normally used in Differential Adsorbtion?
What must the cells be negative for?
One cell is usually R1R1 and another is R2R2 and the third is rr
one for K, one for Jka, and one for Jkb