11.3 Pre-Transfusion Compatibility Testing and Transfusion Reactions

Pre-Transfusion Compatibility Testing and Transfusion Reactions

Compatibility testing is the last laboratory safeguard between a donor unit and a patient. Its goal is to select components that will survive normally in the recipient without causing immune destruction. When a reaction still occurs, the laboratory must quickly separate immune hemolysis from febrile, allergic, pulmonary, volume-related, and septic reactions. This section covers pre-transfusion testing, the classification of transfusion reactions, the laboratory investigation protocol, and a differential matrix. Hemolytic disease of the fetus and newborn and Rh immune globulin are covered in the next section.

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1. Pre-Transfusion Compatibility Testing Protocol

Compatibility testing encompasses all pre-transfusion procedures designed to ensure that donor erythrocytes will survive in the patient circulation without triggering an immune destruction cascade.

                         ┌──────────────────────────────────────────────┐
                         │   Patient Identification & Phlebotomy        │
                         │   • Positive 2-identifier verification       │
                         │   • Tube labeled at bedside in presence of pt│
                         │   • Sample validity: 3 days (72 hours)       │
                         └──────────────────────┬───────────────────────┘
                                                │
                                                ▼
                         ┌──────────────────────────────────────────────┐
                         │      Blood Bank Testing of Recipient         │
                         │   • ABO Forward (cell) & Reverse (serum)     │
                         │   • Rh (D) Typing (antigen D typing)         │
                         │   • Antibody Screen (IAT with 2-3 cell sets) │
                         └──────────────────────┬───────────────────────┘
                                                │
                 ┌──────────────────────────────┴──────────────────────────────┐
                 ▼ Screen Negative / No History                                ▼ Screen Positive OR History
  ┌──────────────────────────────┐                              ┌──────────────────────────────┐
  │   Immediate Spin Crossmatch  │                              │      Full AHG Crossmatch     │
  │ • Recipient serum + donor RBC│                              │ • Recipient serum + donor RBC│
  │ • Detects ABO mismatch only  │                              │ • 37°C incubation + AHG      │
  │ • Validated computer match   │                              │ • Mandatory panel antibody ID│
  │   permitted as alternative   │                              │ • Phenotypically matched units│
  └──────────────┬───────────────┘                              └──────────────┬───────────────┘
                 │ Compatible                                                  │ Compatible
                 └──────────────────────────────┬──────────────────────────────┘
                                                ▼
                         ┌──────────────────────────────────────────────┐
                         │     Clinical Release & Bedside Verification  │
                         └──────────────────────────────────────────────┘

Sample Collection and Validity Rules

• Patient Identification: Phlebotomists must verify the patient's identity using at least two independent identifiers (full legal name and hospital identification number) on the patient's wristband. Tubes must be labeled at the patient's bedside in their immediate presence; pre-labeling tubes is strictly prohibited.
• Specimen Timing ($72\text{ Hour / 3-Day Rule}$): If a patient has received a transfusion or has been pregnant within the preceding 3 months (90 days)—or if history is unknown—the pre-transfusion blood specimen must be collected within 3 days (72 hours) of the scheduled transfusion. This restriction prevents missed emergent alloantibodies generated during secondary anamnestic immune responses.

ABO and Rh (D) Typing

• ABO Grouping: Requires both Forward Grouping (front typing: testing recipient red cells with reagent anti-A, anti-B, and anti-A,B) and Reverse Grouping (back typing: testing recipient serum/plasma with reagent $A_1$ and $B$ red cells). Any discrepancy between front and back typing must be fully resolved before releasing non-emergent blood.
• Rh (D) Typing: Testing recipient red cells with anti-D reagent. Testing for weak D is mandatory on blood donors (to prevent transfusing weak D units to Rh-negative recipients), but is not required for routine transfusion recipients (recipients with negative immediate-spin D typing are designated Rh-negative and issued Rh-negative blood).

Antibody Screening and Identification

• Antibody Screen: Utilizes the Indirect Antiglobulin Test (IAT) to test recipient serum/plasma against a set of 2 or 3 unpooled reagent Group O red blood cells phenotyped for all major clinically significant red cell antigens ($D, C, c, E, e, K, k, Fy^a, Fy^b, Jk^a, Jk^b, M, N, S, s, Le^a, Le^b, P_1$). Enhancement media include Low Ionic Strength Saline (LISS) or Polyethylene Glycol (PEG).
• Antibody Identification Panel: If the screening test is positive, an antibody identification panel of 11 to 20 phenotyped Group O red cell reagents is evaluated:
  • The Rule of Three: To achieve statistical confidence ($p < 0.05$), the technician must demonstrate reactivity with 3 antigen-positive panel cells and non-reactivity with 3 antigen-negative panel cells.
  • Dosage Effect Consideration: Clinically significant blood group systems demonstrate gene dosage (stronger agglutination with homozygous antigen expression than heterozygous): Rh ($C, c, E, e$), Duffy ($Fy^a, Fy^b$), Kidd ($Jk^a, Jk^b$), and MNSs ($M, N, S, s$). Panel rule-outs must be confirmed using homozygous donor cells (e.g., $Jk(a+b-)$) to avoid false-negative exclusions of weak antibodies.
  • Autocontrol and DAT: An autocontrol (patient serum + patient red cells) and Direct Antiglobulin Test (DAT) run in parallel differentiate alloantibodies (negative autocontrol) from autoantibodies or drug-induced antibodies (positive autocontrol).

Major Crossmatch Classifications

The Major Crossmatch combines recipient serum or plasma with donor red blood cells:

1. Immediate Spin (IS) Crossmatch:
   • Recipient serum and donor red cells are centrifuged immediately at room temperature without incubation.
   • Function: Confirms ABO compatibility between donor unit and patient; it does not detect non-ABO atypical IgG antibodies.
   • Prerequisites: Permitted ONLY if the recipient's antibody screen is completely negative AND there is no historical record of clinically significant atypical red cell alloantibodies.
2. Full Antiglobulin (AHG) Crossmatch:
   • Incorporates $37^\circ\text{C}$ incubation followed by a thorough saline wash ($3\text{--}4$ cycles) and the addition of Anti-Human Globulin (AHG) reagent.
   • Function: Detects clinically significant IgG alloantibodies directed against donor surface antigens.
   • Prerequisites: MANDATORY if the recipient has a currently positive antibody screen OR a historical record of clinically significant antibodies, even if current titers appear undetectable.
3. Computer / Electronic Crossmatch:
   • Validated computer software compares donor unit barcode data with recipient laboratory records.
   • Prerequisites: Requires two independent determinations of recipient ABO type on file, a confirmed negative antibody screen with no historical antibodies, and automated data entry verification.

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2. Transfusion Reactions: Classification and Pathophysiology

Adverse transfusion reactions are classified by time of onset into acute ($<24\text{ hours}$) and delayed ($>24\text{ hours}$ to several weeks):

Acute Transfusion Reactions ($<24\text{ Hours}$)

• Acute Hemolytic Transfusion Reaction (AHTR):
  • Primary Cause: Clerical or patient-misidentification error resulting in the infusion of ABO-incompatible red blood cells.
  • Pathophysiology: Recipient preformed IgM isohemagglutinins (anti-A, anti-B) bind to donor red cells, potently activating the classical complement pathway to completion (C5b-9 Membrane Attack Complex). This causes rapid, catastrophic intravascular hemolysis.
  • Clinical Manifestations: Rapid onset of fever, rigors/chills, severe burning sensation at venipuncture site, excruciating substernal chest and flank/lumbar back pain, profound hypotension, tachycardia, hemoglobinemia, hemoglobinuria, Disseminated Intravascular Coagulation (DIC), and acute oliguric renal failure (from immune complex deposition, microvascular thrombosis, and free heme nephrotoxicity).
• Febrile Non-Hemolytic Transfusion Reaction (FNHTR):
  • Definition: Temperature elevation of $\ge 1.0^\circ\text{C}$ ($1.8^\circ\text{F}$) above baseline during or within 4 hours of transfusion, in the absence of hemolysis or other causes.
  • Mechanism: Recipient cytotoxic antileukocyte antibodies reacting against donor leukocyte HLA antigens, or the passive infusion of pyrogenic cytokines (IL-1$\beta$, IL-6, TNF-$\alpha$, IL-8) accumulated in the donor plasma during storage.
  • Management and Prevention: Treated with antipyretics (acetaminophen); prevented by pre-storage leukoreduction.
• Allergic and Anaphylactic Reactions:
  • Mild Allergic (Urticarial): Recipient IgE antibodies reacting against donor plasma proteins, inducing mast cell and basophil degranulation with localized histamine release. Manifests as pruritus, hives (urticaria), and erythema without fever. If only mild hives occur, transfusion may temporarily pause, antihistamines (diphenhydramine) administered, and if resolved, transfusion may resume.
  • Severe Anaphylactic Shock: Sudden, catastrophic reaction developing within seconds to minutes after infusing only a few milliliters of blood. Characterized by severe bronchospasm, laryngeal edema, substernal chest tightness, cyanosis, abdominal cramping, and cardiovascular collapse in the complete absence of fever.
  • High-Yield Etiology: Occurs in individuals with congenital IgA deficiency who have synthesized circulating anti-IgA antibodies (class-specific IgG or IgE). Transfusion of any plasma-containing component introduces donor IgA, triggering anaphylaxis. Treated with immediate intramuscular epinephrine; future transfusions mandate thoroughly washed red blood cells or components from confirmed IgA-deficient donors.
• Transfusion-Related Acute Lung Injury (TRALI):
  • Clinical Picture: Acute onset of severe hypoxemic respiratory distress ($PaO_2/FiO_2 \le 300\text{ mm Hg}$ or $SpO_2 < 90\%$ on room air) and bilateral pulmonary infiltrates on chest X-ray developing within 6 hours of transfusion.
  • Pathogenesis: Non-cardiogenic pulmonary edema. Most commonly triggered by donor anti-HLA Class I/II or anti-HNA (neutrophil-specific) antibodies present in plasma-rich components (especially multiparous female donors). The antibodies bind recipient pulmonary capillary neutrophils, causing neutrophil activation, degranulation, endothelial injury, and massive capillary leakage into pulmonary alveoli.
  • Differential Biomarkers: TRALI features normal B-type natriuretic peptide (BNP), normal central venous pressure, normal jugular venous pressure, and hypotension or normal blood pressure. Together with TACO, it is one of the two leading causes of transfusion-related death.
• Transfusion-Associated Circulatory Overload (TACO):
  • Pathogenesis: Cardiogenic (hydrostatic) pulmonary edema caused by excessive volume or overly rapid transfusion infusion rate, particularly in elderly patients, chronic severe anemia, or underlying cardiopulmonary disease.
  • Clinical Manifestations: Severe dyspnea, cyanosis, orthopnea, hypertension (systolic spike), tachycardia, bounding pulses, headache, and distended neck veins (elevated JVP).
  • Differential Biomarkers: TACO features markedly elevated BNP or NT-proBNP ($>1.5$-fold increase over baseline) and post-transfusion central venous hypertension. Responds rapidly to stopping the infusion, placing the patient upright, supplemental oxygen, and intravenous loop diuretics (furosemide).
• Transfusion-Transmitted Sepsis (Septic Shock):
  • Sudden onset of high fever ($>2^\circ\text{C}$ rise), severe rigors, hypotension, and warm shock resulting from bacterial contamination. Most common in platelet concentrates stored at $20\text{--}24^\circ\text{C}$ (Staphylococcus epidermidis, Staphylococcus aureus, Serratia marcescens) or cold-tolerant organisms in red cells (Yersinia enterocolitica, Pseudomonas fluorescens).

Delayed Transfusion Reactions ($>24\text{ Hours}$)

• Delayed Hemolytic Transfusion Reaction (DHTR):
  • Onset: Typically occurs $3\text{ to }14\text{ days}$ post-transfusion.
  • Pathogenesis: Anamnestic (secondary) immune response. The recipient had previously been sensitized by pregnancy or transfusion, but the circulating antibody titer declined below the analytical detection threshold during pre-transfusion testing. Re-exposure to the foreign antigen boosts memory B-cells, prompting rapid synthesis of IgG alloantibodies.
  • Classic Etiology: Famously associated with antibodies of the Kidd Blood Group System (anti-$Jk^a$, anti-$Jk^b$), notorious for dropping to undetectable levels and exhibiting dosage. Other culprits include Rh ($c, E$) and Duffy ($Fy^a$).
  • Hemolysis Mechanics: Extravascular hemolysis mediated by splenic and hepatic reticuloendothelial macrophages. Symptoms are mild: unexplained drop in hemoglobin/hematocrit, low-grade fever, mild indirect hyperbilirubinemia, and spherocytosis. Post-transfusion Direct Antiglobulin Test (DAT) is characteristically positive with a mixed-field pattern.
• Transfusion-Associated Graft-versus-Host Disease (TA-GVHD):
  • Occurs $1\text{ to }4\text{ weeks}$ post-transfusion when immunocompetent donor T-lymphocytes engraft and proliferate in a recipient, attacking host tissues.
  • Manifests as profound pancytopenia (bone marrow aplasia), maculopapular skin rash, profuse watery diarrhea, and abnormal liver function. Greater than $90\%$ fatal; prevented exclusively by gamma irradiation (25 Gy).

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3. Emergency Transfusion Reaction Investigation Protocol

When a transfusion reaction is suspected, the clinical team and the blood bank must execute an immediate, standardized sequence of emergency actions:

┌────────────────────────────────────────────────────────────────────────────────────────┐
│                      Emergency Transfusion Reaction Protocol                           │
├────────────────────────────────────────────────────────────────────────────────────────┤
│ 1. STOP THE TRANSFUSION IMMEDIATELY! Keep IV line open with normal saline.             │
│ 2. Perform Immediate Bedside Clerical Check (Unit tag, bag label, wristband).          │
│ 3. Notify attending physician and Blood Bank immediately.                              │
│ 4. Return blood bag, attached infusion set, and IV fluids to Blood Bank.               │
│ 5. Collect post-reaction EDTA pink-top, plain red-top blood tubes, and fresh urine.    │
├────────────────────────────────────────────────────────────────────────────────────────┤
│                             Immediate Blood Bank Workup                                │
│                                                                                        │
│  [Clerical Re-Check] ───────► Match requisition, unit label, patient crossmatch records│
│                                                                                        │
│  [Visual Serum Check] ──────► Centrifuge pre- & post-reaction tubes side-by-side:      │
│                               • Pink/Red = Free hemoglobin (intravascular hemolysis)   │
│                               • Brown/Amber = Icterus / Bilirubinemia                  │
│                                                                                        │
│  [Post-Transfusion DAT] ────► Direct Antiglobulin Test on post-reaction EDTA cells:    │
│                               • Positive Mixed-Field = Donor cells coated with antibody│
│                                                                                        │
│  [Repeat ABO / Rh] ─────────► Retype pre-sample, post-sample, and residual bag blood   │
└────────────────────────────────────────────────────────────────────────────────────────┘

Step-by-Step Laboratory Workflow

1. Immediate Bedside Actions:
   • STOP the transfusion immediately. Disconnect the blood infusion set at the hub. Do not flush the line with residual blood!
   • Maintain patent vascular access using sterile $0.9\%\text{ normal saline}$ via fresh primary IV tubing.
   • Perform an immediate bedside clerical check comparing the blood container label, compatibility tag, medical record, and patient wristband.
   • Promptly alert the blood bank and primary physician; dispatch the intact blood container, IV tubing, and all attached solutions to the laboratory.
2. Specimen Collection:
   • Draw fresh post-transfusion blood samples (EDTA pink/lavender-top and non-anticoagulated red-top) avoiding collection from the same extremity as the transfusion.
   • Collect the first voided post-transfusion urine sample to assess for hemoglobinuria.
3. Immediate Blood Bank Testing (Mandatory Initial Triad):
   • Clerical Check: Verify all documentation, specimen labeling, blood unit identification numbers, and crossmatch reports for clerical transcription errors.
   • Visual Serum Inspection: Centrifuge the pre-transfusion and post-transfusion blood specimens side-by-side. Inspect the supernatant plasma: pink or bright red discoloration in post-transfusion plasma that is absent pre-transfusion confirms free hemoglobin ($>25\text{--}50\text{ mg/dL}$) released by intravascular hemolysis. Brown discoloration indicates methemalbumin formation.
   • Direct Antiglobulin Test (DAT): Perform a DAT on the post-transfusion EDTA sample using polyspecific and anti-IgG reagents. A positive DAT with a mixed-field agglutination pattern indicates that circulating transfused donor red cells are coated with recipient alloantibody.
   • Repeat ABO and Rh Grouping: Concurrently retest pre-transfusion patient sample, post-transfusion patient sample, and residual blood expressed directly from the donor blood container.
4. Secondary Confirmatory Workup:
   • If any initial test is positive or hemolysis is suspected: repeat antibody screen and full crossmatch; quantify plasma free hemoglobin and serum haptoglobin (profoundly depressed or zero in intravascular hemolysis); measure total and indirect bilirubin ($4\text{ to }6\text{ hours}$ post-reaction); test urine for hemoglobin and hemosiderin (Prussian blue stain on spun sediment); perform Gram stain and blood cultures on the donor bag and patient blood.

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4. Transfusion Reaction Differential Diagnostic Matrix