7.3 Transfusion Reactions: Investigation Protocol and Reaction Classification

Transfusion Reactions and Investigation Protocol

Despite stringent safety measures, adverse events related to blood transfusions can occur. Transfusion reactions range from mild allergic responses to fatal hemolytic events. Rapid recognition and a systematic laboratory investigation are essential to manage the patient and prevent similar occurrences.

Immediate Actions: The Transfusion Reaction Protocol

When a transfusion reaction is suspected (e.g., patient complains of chills, pain, shortness of breath, or fever), the clinical staff must act immediately:

1. STOP the transfusion immediately. This is unequivocally the most important first step.
2. Keep the IV line open by infusing normal saline (0.9% NaCl).
3. Check all labels, tags, and patient identification wristbands for any clerical errors.
4. Notify the attending physician and the blood bank.
5. Send the remaining blood unit and tubing back to the blood bank.
6. Draw a post-reaction blood sample (EDTA tube) carefully to avoid mechanical hemolysis, and collect a post-reaction urine sample.

Laboratory Investigation

Upon receiving the post-reaction samples and blood unit, the blood bank initiates a standardized workup to rule out a hemolytic event.

• Clerical Check: Verify all paperwork, labels, and computer records. Clerical errors are the leading cause of fatal hemolytic reactions.
• Visual Inspection: Centrifuge the post-reaction blood sample and visually compare the plasma/serum to the pre-reaction sample. Pink or red plasma indicates hemoglobinemia (intravascular hemolysis). Icteric (yellow) plasma may indicate delayed hemolysis.
• Direct Antiglobulin Test (DAT): Perform a DAT on the post-reaction red cells. A positive DAT (mixed field) indicates that antibodies have attached to the transfused donor cells in vivo.
• ABO/Rh Confirmation: Repeat the ABO and Rh typing on the post-reaction sample and compare it to the pre-reaction sample and the donor unit.
• Urine Check: Test the post-reaction urine for free hemoglobin (hemoglobinuria).

If the DAT is positive, or hemolysis is visually evident, the blood bank must proceed to elution, antibody screening, and crossmatching to identify the specific incompatibility.

Classification of Transfusion Reactions

Acute Hemolytic Transfusion Reaction (AHTR)

• Mechanism: Immune-mediated destruction of donor red cells, usually due to ABO incompatibility (e.g., Group A blood given to a Group O patient). IgM antibodies activate complement fully, causing rapid intravascular hemolysis.
• Symptoms: Fever, chills, lower back/flank pain (due to kidney involvement), hypotension, hemoglobinuria, and a feeling of impending doom. It can progress to Disseminated Intravascular Coagulation (DIC) and renal failure.
• Lab Findings: Positive DAT, visible hemolysis in plasma, decreased haptoglobin, and hemoglobin in urine.

Febrile Non-Hemolytic Transfusion Reaction (FNHTR)

• Mechanism: Most commonly caused by recipient antibodies attacking donor human leukocyte antigens (HLA) or by cytokines that accumulate in the blood component during storage.
• Symptoms: A temperature rise of >= 1°C above baseline, accompanied by chills or rigors, without any evidence of hemolysis.
• Prevention: Provision of leukoreduced blood products significantly reduces the incidence of FNHTR.

Allergic and Anaphylactic Reactions

• Mechanism: Mild allergic reactions (urticaria/hives) are caused by recipient antibodies reacting to donor plasma proteins. Severe anaphylactic reactions occur in patients who are IgA-deficient and have developed anti-IgA antibodies; when exposed to IgA in donor plasma, they rapidly develop shock.
• Symptoms:
  • Mild: Hives, itching, erythema (can often be treated with antihistamines and the transfusion restarted if only urticaria is present).
  • Severe: Bronchospasm, wheezing, profound hypotension, absent fever.
• Prevention: Washed cellular products (to remove plasma) for known IgA-deficient patients.

Transfusion-Related Acute Lung Injury (TRALI)

• Mechanism: A leading cause of transfusion-related mortality. It is triggered by donor antibodies (anti-HLA or anti-HNA) in the plasma of the blood product that react with the recipient's white blood cells. These WBCs aggregate in the pulmonary vasculature, causing capillary leakage and noncardiogenic pulmonary edema.
• Symptoms: Acute respiratory distress, severe hypoxemia, and bilateral pulmonary infiltrates on chest X-ray within 6 hours of transfusion.
• Prevention: Deferring female donors with a history of pregnancy from donating plasma products, as they are most likely to possess these alloantibodies.

Transfusion-Associated Circulatory Overload (TACO)

• Mechanism: Non-immune volume overload resulting from infusing blood products too rapidly or in too high a volume, overwhelming the patient's cardiovascular system (common in elderly patients, infants, or those with underlying heart/renal failure).
• Symptoms: Dyspnea, orthopnea, tachycardia, hypertension, and pulmonary edema.
• Differentiation from TRALI: TACO is characterized by hypertension and an elevated BNP (Brain Natriuretic Peptide), whereas TRALI is often associated with hypotension and normal BNP. TACO responds well to diuretics.

Understanding these distinct reactions ensures rapid, appropriate medical intervention and prevents catastrophic outcomes in transfusion medicine.