Chapter 10 Pretransfusion Testing

• Pretransfusion testing encompasses a series of serologic and nonserologic protocols to prevent immune-mediated hemolytic transfusion reactions, enhancing blood transfusion safety.

Testing Standards

• Transfused red blood cells (RBCs) should have an acceptable survival rate without significant destruction of the recipient's own RBCs.
• Pretransfusion testing, adhering to AABB standards, is vital for safe blood transfusion therapy.
• Pretransfusion testing cannot guarantee normal survival of transfused RBCs, necessitating a risk-benefit analysis for each transfusion.
• CLIA '88 regulates pretransfusion testing, including ABO group, Rh type, antibody detection and identification, and crossmatch testing.

Identification, Collection, and Preparation of Samples

• Pretransfusion testing relies on proper patient sample identification and collection, ensuring recipient safety and acceptable survival rates.

Positive Recipient Identification

• A primary cause of transfusion-related fatalities is clerical error, resulting in ABO-incompatible transfusions, with 47% of errors involving patient or blood misidentification in a New York study.
• Misidentification during sample drawing, lab handling, or transfusion administration is a common clerical error.
• Compare the facility-generated recipient ID wristband with the blood requisition form, which must include the recipient's full name and unique hospital identification number.
• While not required, verifying patient identity is essential; illegible printing and handwritten forms are discouraged in favor of indelible nameplate impressions or computer printouts.
• Resolve any discrepancies before sample collection, and never use wall or bed labels for identity verification.

Collection of Patient Samples

• Blood samples should be drawn carefully to avoid hemolysis to allow detection of hemolysis caused by antigen-antibody complexes that activate completement.
• Note the extent of hemolysis in patient serum or plasma, especially in individuals with in vivo hemolytic processes.
• Plasma or serum may be used for testing
• About 10 mL of blood is generally sufficient for testing.
• Tubes must be labeled at the bedside with the patient's full name, unique identification number, and collection date.
• Avoid contamination by not taking samples from IV tubing lines; draw samples from below the infusion site.
• Blood bank personnel must confirm the agreement of sample information and requisition forms.
• Test recipient samples ASAP, storing them at 1°C to 6°C if immediate testing isn't possible.
• Recent pregnancy or transfusion indicates opportunity for a humoral immune response, collect samples during the critical phases.
• Serum obtained from samples collected in under 72 hours from certain patients must be used for antibody screening and crossmatch testing.
• Patient RBCs can be obtained from clotted or anticoagulated samples, washed with saline before use to remove serum.
• Prepare a 2%-5% saline suspension for most serologic testing, consulting the manufacturer's instructions for specific reagents.

Collection of Donor Samples

• Donor samples must be collected with the full donor unit, labelled, and verified.
• Use a donor unit identification number for all records and component disposition.
• RBCs for donor pretransfusion testing can be prepared from the segmented tubing on the collection bag, which must display the same numbers as the bag.

Testing the Donor Sample

• ABO grouping, Rh typing (including a test for weak D), and disease transmission prevention tests must be performed on the donor blood samples.
• Unexpected antibodies screening is required on donor samples with a history of transfusions or pregnancy.

Testing the Patient Sample

• ABO, Rh, and antibody screening test results should be included in the patient's record, along with notes on unusual serologic reactions and any unexpected antibodies.
• If the patient has been pregnant or transfused within the last 3 months obtain the sample to be tested from within 3 days of scheduled testing
• An accurate medical history is helpful to explain unusual results.

ABO Grouping

• Determining the correct ABO group is the most critical pretransfusion serologic test.
• Perform additional testing to resolve discrepancies.
• If the ABO group cannot be determined, use group O-packed RBCs when an immediate transfusion is required.

Rh Typing

• Perform Rh typing using anti-D blood typing reagents, following the manufacturer's directions for the reagent and running indicated controls.
• Perform a DAT on the patient's RBCs to determine whether uptake of autoantibodies or alloantibodies (if the recipient was recently transfused) is responsible for the positive control.

Antibody Screening

• The recipient's serum or plasma should be tested for clinically significant unexpected antibodies.
• "Clinically significant unexpected antibody" references antibodies known to cause transfusion reactions or unacceptably short survival of transfused RBCs.
• Incidence is due to allogeneic transfusion of RBCs, pregnancy, or transplantation.
• Specimens used in pretransfusion testing should ideally be collected during the critical phases of the immune response by recent pregnancy or recent medical precedures.

Selection of Appropriate Donor Units

• Transfuse blood and blood components of the patient's own ABO and Rh group.
• If units selected must not contain clinically significant antibodies.
• Only packed RBCs can be given if someone must be given blood of a differing ABO group.
• Avoid large quanties of Group O blood as they could be used for others.
• Perform the crossmatch including incubation at 37°C and the AHG test. Ensure it is the right antibody.

Crossmatch Testing

• Test the patient's serum with their donor RBC's including an antiglobulin phase or immedaite spin to confirm ABO compatability.
• Value to perfoming serologic is to check ABO compatabilty or antibodies in the patient's serum not detected in antibody testing.
• AABB states it is sufficient to be to detect ABO incompatibility if no clinically significant antibodies have been detected.

Immediate Spin Crossmatch

• If there are no clinically significant unexpected antibodies present test to detect the ABO incompatability.
• Mix the recipents serum with the donor RBC's with immediate spin. No hemolysis or agglutination indicates ABO compatibility.
• Type screen involves testing the patient's blood sample for ABO, RH and clinically significant unexpected antibodies and storing it.
• In the event of transfusion perform the procedure.
• Studies show 99.9% effective in preventing occurance in an incompatible reaction.

Antiglobulin Crossmatch

• This process begins the same way as Immedate Spin, continuing to 37C incubation and ending with an antiglobulin test for the greatest sensitivity of the antihuman globulin.
• Run an autocontrol in parallel by using the patients own cells and serum. Though the Standars of AABB no longer requires controls this helps clarify outcomes.

Interpretation Of Results

• Tubes should be cafrefully layered so contents are identified at any stage. A Jaggerd or firm button edge is indicative of a positive agglutination reaction, unlike a smooth swirling indication.
• False negative results may occur if shaking occurs or in patients with hypertension.
• Uniform grading and microscoping examination should occur to properly note findings.
• All results must be immiediately record.

Resolution Of Incompatibilities in the Serologic Crossmatch

• Primary objective is to detect the presence of anti-A or anti-B
• Positive result requires explanation to identify source of the problem.

Causes of Positive Results in the Serologic Crossmatch

• Inccorect ABO grouping of the patient or donor, requires an immedate repeat.
• Alloantibody reacting with corresponding antigen.
• Autoantibody
• Prior Coating
• Abnormalities

Resolution

• For example antibodies like anti-Al may occur. Check patients transfusion and transplat historeis.
• Donor RBC should be compatible with all recepient tested with the AHG phase.

Computer Crossmatch

• Is electronic
• Compares ABO serologic results
• Butch indicates an execelnt model of how a crossmatch should operate.
• Needs approval from the AABB

Pretransfusion in Special Circumstances

• Needs in emergency take precedence over any standadrs.

Emergency Transfusion

• ABO and Rh should be determined

Transfusion of Non-Group Specific Blood

• Perform anti-A or anti-B for the receipients own ABO before transfusion.

Preoperative Autologous Blood

• ABO group testing is not necessary

Limitations of Compatibility Testing

• Guarntee of a blood unit after transfusion cannot be achieved. In conclusion, give blood if there is a need to survive.

Blood Inventory Management

• Maximise the number of blood banks available.
• The Maximim Surgical Blood Order Schedule promotes this to occur for effient utilisation of ordering levels.

Reidentification of the Patient Before Transfusion

Testing Schemes

• Make sure to adhere to patient identification

• Hold Clot

• Type and screen

Reidentification

• Record who is receiving blood so if transfusion is needed this information is known.
• Have some type of check so issues do not occur like mistransfusions.

Future Pretransfusion Testing

• Automation is used to identify how much the volume can be used and how much is safe without contamination.