Immunohematology - 12 Compatibility Testing

• IMMUNOHEMATOLOGY BLOOD BANKING PROCEDURES: COMPATIBILITY TESTING OUTLINE • Compatibility Testing o Collection and Preparation of Samples o Compatibility Testing Protocols o Crossmatching • • COMPATIBILITY TESTING • • • A pretransfusion procedure performed to ensure the safety of the patient during and after blood transfusion o Prevents transfusion reaction that can lead to series of complications Called crossmatching because the patient’s sample are tested against the donor’s sample Takes 1 hour to complete COMPATIBILITY TESTING PROTOCOLS • COLLECTION AND PREPATION OF SAMPLES • • • • • • • Patient Identification. o Important to prevent clerical error Collection Serum is the preferred specimen for compatibility testing because it lacks fibrinogen which fibrin clots may cause false positive o Uses red top/plain top o Do not use SST o Ensure proper clotting Hemolysis should be avoided. o May cause false positive Ag-ab reactions are based on o Hemolysis o Agglutination Why serum and not plasma? o Plasma may cause small fibrin clots to form which may be difficult to distinguish from true agglutination o Plasma may inactivate complement so that antibodies may not be detected Age of Specimen o The freshest sample possible should be used for compatibility testing. ▪ Fresh sample must be tested immediately ▪ Pilot tube - cut from the tube attached to the blood bag that is used for testing ▪ Patient samples should be kept for 7-14 days for retesting o Specimens must be less than 3 days old if the patient has been transfused or pregnant within the past 3 months. o Must be 3 days old because it represents the current or actual immunologic status of the patient o If autologous procedure, it must always be retyped o In case of emergency, safest blood to give is blood type O- pRBC because it lacks highly immunogenic ABO Ag (AB plasma lacks high titer anti-A, anti-B, and anti-AB that’s why it is not safe for transfusion) Sample Storage o AABB requires that patient samples must be stored between 1-6C for at least 7 days after transfusion o The crossmatch sample store at ref. temp. is used in the investigation of transfusion reaction if it appears/occurs in the patient Use of Check Cell/Control Cell o Used to validate all negative AHG test reaction o To be valid, check cell must give a positive agglutination reaction o To check for the reaction of reagent Invalid Check Cell Result (negative; w/o agglutination) o Reagent is deteriorating o AHG is already neutralized o Not washed properly • ABO Grouping o Most critical pretransfusion serologic test ▪ Any incompatibility can cause the most severe transfusion reaction which is Acute Immunologic Hemolytic Transfusion Reactions (AIHTR) that can be manifested within 24 hours o If the patient’s ABO group cannot be satisfactorily determined and immediate transfusion is essential, group O packed RBCs should be utilized Rh Typing o If Rh type of the recipient cannot be determined and transfusion is essential, Rh-negative blood should be given CROSSMATCHING • • • Major X-Match: Donor’s cells (ag) + Recipient’s serum (ab) (PS + DR) = (P ab + D ag) Minor X-Match: Donor’s serum (ab) + Recipient’s cells (ag) (PR + DS) = (P ag + D ab) After 14 days → longest transfusion reaction 3 PHASES OF CROSSMATCHING • • • • Immediate Spin in saline at Rt → detects IgM o M → centrifuge → 20 secs → check aggltn/hemolysis Thermophase/37ºC with enhancement medium (e.g. albumin, LISS, PEG) → Detects IgG o M + EM → 30-45 mins → centrifuge → check AHG Phase after washing incubated cells with saline. o M + AHG → centrifuge → check o Detect non-agglutinating ab *Check cells/Coombs control cells (IgG sensitized cells) should be added to tubes that demonstrate no agglutination. For results to be considered valid, agglutination must occur. TECHNIQUES IN CROSSMATCHING • • Saline Technique o PS + DR in saline medium o IgM detection at RT o Detects ABO incompatibilities High Protein (albumin) o PS + DR in albumin medium/enhancement o IgG detection at 37C o Detects Rh incompatibilities • • AHG Technique o PS + DR in AHG medium o IgG detection at 37C o Detects Duffy, Kidd, kell antibodies Broad Spectrum Technique o IgM and IgG are detected REPORTING OF RESULTS • • • • • • • A compatible crossmatch is indicated by by absence of agglutination and/or hemolysis at any stage of crossmatch The absence of agglutination indicates that the patient has no demonstrable antibodies with a specificity for any antigen on donor’s RBCs Case 1 o Major - Neg (compatible) o Minor - Neg (compatible) o Release blood to the ward Case 2 o Major - Neg (compatible) o Minor - Pos (incompatible) o Release blood as packed RBCs (remove the plasma Case 3 o Major - Pos (incompatible) o Minor - Neg (compatible) o Do not release the blood to the ward Case 4 o Major - Pos (incompatible) o Minor - Pos (incompatible) o Never release the blood Example Case 1 o Patient - O ▪ Ag: H ▪ Ab: anti-A, anti-B o Donor - B ▪ Ag: B, H ▪ Ab: anti-A o Major ▪ PS + DR ▪ PS: O → anti-A, anti-B ▪ DR: B → B, H ▪ Incompatible o Minor ▪ PR + DS ▪ PR: O → H ▪ DS: B → anti-A ▪ Compatible o Reporting ▪ Major: Incompatible ▪ Minor: Compatible ▪ Do not release the unit • Example Case 2 o Patient - AB ▪ Ag: A, B, H ▪ Ab: none o Donor - B ▪ Ag: H ▪ Ab: anti-A, anti-B o Major ▪ PS + DR ▪ PS: AB → none ▪ DR: O → H ▪ Compatible o Minor ▪ PR + DS ▪ PR: AB → A, B, H ▪ DS: O → anti-A, anti-B ▪ Incompatible o Reporting ▪ Major: Compatible ▪ Minor: Incompatible ▪ Do not release the unit INCOMPATIBLE CROSSMATCHES Reactions Neg ab screen, Incompatible IS Xmatch 1 ab screening cell and 1 donor pos in AHG Ab screening cells and all donors except 1 neg at 37degC and in AHG. 1 donor pos in AHG only. Ab screening cells, donors and AC positive in AHG Ab Screening cells, donors and AC positive at 37degC, neg AHG Possible Cause Resolution ABO Retype donor and incompatibility recipient. Xmatch with ABO compatible donor Alloantibody Identify ab. Xmatch units neg for corresponding ag Positive DAT on Perform DAT on unity (if donor positive, return to collecting facility) Warm autoantibody Rouleaux Not to transfuse. If unavoidable, find “least incompatible unit” Saline replacement technique