T5+6 - Pre-Transfusion Testing Flashcards
What is Pre-Transfusion Testing?
All checking/testing that is involved in providing transfusion recipients with blood products to ensure the product has an acceptable survival and doesn’t result in destruction of the recipient’s RBCs
Aim is to maximise the benefit to the recipient while minimising the risk
Performed before administration of a blood component that could result in the formation of antigen-antibody complexes
Steps Involved in Pre-Transfusion Testing
Sample collection - request form - collection - appropriate sample ABO and Rh(D) grouping Antibody Screen (and ID if required) Selection of appropriate donor Cross-match Transfusion
Sample Collection
Blood for transfusion testing is usually collected into EDTA
Sample is labelled after collection but before leaving the recipient
Recipient’s full name, hospital identifier or DOB, and date and time of collection are hand-written on tube
Samples that don’t meet all of these requirements must be discarded
Specimen Storage
Whole blood (EDTA) and separated plasma
- store at 18-25°C for up to 48 hours
- store at 2-8°C for up to 7 days
Separated plasma can be stored at -20°C for up to 3 months
Sample Validity
Patient not transfused or pregnant in past 3 months
- sample is valid for 7 days from collection
- up to 3 months from collection if plasma has been frozen
Patient has been transfused, is pregnant, or has been in past 3 months:
- sample is valid for 72 hours from collection
- anamnestic (secondary) immune response
Antibody Screen
Performed to detect clinically significant antibodies that may be present in the patient plasma
- cause haemolysis of the corresponding antigen positive cells, resulting in HTR or HDNB
- reactive in the indirect antiglobulin test (IAT) @ 37°C
- anti-A, anti-B, and anti-AB must always be considered clinically significant
Use antibody screening cell panel
- 2/3 cells from different donors that have known antigen expression
Antibody Screening Cells
Come from different group O donors
Together, must express C, c, D, E, e, M, N, S, s, K, k, Fya, Fyb, Jka, Jkb, Lea and Leb
One should be R1R1, another should be R2R2
Cells homozygous for Fya, Fyb, Jka, Jkb must be represented, same for S and s also desirable
Together, they express antigens corresponding to the major clinically significant antibodies
Allow us to detect clinically significant antibodies in patient plasma
Patient plasma is reacted against screening cells, screen performed by IAT
Antibody Identification
If an antibody is detected in the recipient plasma, its specificity and clinical significance must be determined
Perform an antibody identification
Use a long cell panel (antibody identification panel)
- contains 8-16 cells with known antigen expression from different donors
- allows confident identification of the antibody present
Use at least the same technique as used in the screen
Including an auto control can be helpful
- react patient cells against patient plasma
- if negative, an alloantibody is present
- if positive, an autoantibody (+/- an alloantibody is present)
Detecting Antibodies
Aby ID is performed at least by IAT
If performing the IAT by tube, it can be performed in 3 phases:
1. Immediate spin
- mix patient plasma with panel cells, spin, read result
- detects IgM antibodies
2. 37°C
- mix patient plasma with panel cells, incubate @ 37°C, spin, read result
- detects IgM that reacts at 37°C, and some v. strong IgG’s
3. AHG Phase
- mix patient plasma with panel cells, incubate @ 37°C, wash cells, add AHG, read result
Process of Antibody Identification
- For negative reactions, cross out the antigens expressed on the corresponding cell
- called “crossing out”, “rule out”, or exclusion
- when required, you have to rule out on cells that have homozygous expression of the corresponding antigen
- anti –Jka, -Jkb, -Fya, -Fyb, -S, -s
- anti –M too!! - Match the pattern
- 2+2 rule
- to confirm the antibody identity, it must react with 2 cells carrying the antigen, and not react with 2 cells lacking the antigen
- can include cells from the antibody screen
Selection of Appropriate Donor
Wherever possible, the donor RBCs should be the same ABO and Rh(D) group as the patient
If the recipient has EVER produced a clinically significant antibody, RBCs not expressing the corresponding antigen should be chosen
- called “antigen negative” cells
If an antibody is present that is not considered clinically significant, can issue “IAT cross-match compatible” cells
Cross-Match
Performed to ensure that donor RBCs will not be destroyed when transfused into patient
React recipient plasma against donor RBCs
Negative reaction = recipient is compatible with donor
3 types
Types of Cross-Match
Immediate spin (IS)
- confirms ABO compatibility only
- use ONLY if the recipient has NEVER had a clinically significant antibody detected in their plasma
IAT
- confirms ABO compatibility and compatibility with other blood groups
- use if a clinically significant antibody has EVER been detected in the recipient plasma
Electronic/computer
- donor RBCs are released without physically performing a cross-match
- pre-transfusion testing on CURRENT patient sample performed
- no current or historical evidence of clinically significant aby’s
- validated data management system
Transfusion in Emergencies
Provide O Rh(D) neg blood initially Provide group specific blood ASAP Complete pre-transfusion testing ASAP - 10 mins - ABO and Rh(D) group - 30 mins a antibody screen and cross-match Blood must be labelled UNCROSSMATCHED or EMERGENCY ISSUE - COMPATIBILITY TESTING NOT COMPLETED
Group and Screen
A.k.a Group and Hold
ABO/Rh(D) group and antibody screen is performed prior to potential transfusion (i.e. elective surgery)
Selection of unit and cross match is performed when unit is requested
Minimises unnecessary holding of XM’d RBCs for patients who don’t end up needing them
