Acute Transfusion Reactions

Overview

Acute transfusion reactions are a heterogeneous group of complications that occur during or within the first 24 hours of blood or blood product infusion; in practice, most symptoms appear in the first 4-6 hours, while severe ones often start within the first 15 minutes. Because early signs such as fever, chills, dyspnea, hypotension, and pain are non-specific, transfusion is first stopped in any suspected reaction, and the situation is treated as a severe reaction (hemolytic, septic, anaphylactic, or TRALI) until these are ruled out.

The British Society for Haematology (BSH) 2023 guideline states that initial management should be guided by the severity of symptoms and signs without waiting for laboratory results; only in a patient with isolated mild fever without systemic signs can paracetamol be given and the transfusion closely monitored; however, if systemic signs such as chills, rigor, myalgia, nausea, or vomiting are added, bacterial contamination or hemolytic reaction must be considered. Types of reactions differ markedly in frequency: febrile non-hemolytic reaction is the most common type, occurring in approximately 1-3% of units (about 0.3% in red blood cell suspensions and about 4.6% in platelet suspensions); allergic reactions complicate about 1% of transfusions and account for 13-33% of all reactions; the incidence of clinically severe acute transfusion reactions, according to UK hemovigilance data (SHOT), is about 14 per 100,000 components (about 11 for red cells, about 29 for platelets).

Acute hemolytic reaction is generally due to ABO incompatibility, and most cases occur as a result of patient or sample misidentification (clerical error); ABO-incompatible transfusion occurs approximately once in every 38,000 transfusions, about half of which result in a hemolytic reaction, and fatal ABO incompatibility is rare (roughly estimated between 1/600,000 and 1/1,800,000). In pathophysiology, the recipient’s pre-existing natural antibodies bind to donor red blood cells, activate complement, and lead to intravascular hemolysis; fever, back or flank pain, hemoglobinuria, hypotension, disseminated intravascular coagulation, and acute kidney injury can be observed.

Febrile non-hemolytic reaction is linked to cytokines accumulating in the stored product and the recipient's antibodies against donor leukocytes; it manifests with chills and at least a one°C rise in temperature and is a diagnosis of exclusion. Allergic and anaphylactic reactions occur against donor plasma proteins; they range from mild urticaria to anaphylaxis.

While anaphylaxis has classically been attributed to anti-IgA antibodies in confirmed IgA deficiency, IgA deficiency and anti-IgA are found in about one in 1,200 individuals, whereas an anaphylactic reaction occurs only in approximately 1 in 50,000 red cell transfusions; due to this marked discrepancy, it has been shown that most anaphylactic reactions cannot be explained by IgA. TRALI is a non-cardiogenic permeability type pulmonary edema triggered by donor anti-leukocyte (anti-HLA or anti-neutrophil) antibodies or bioactive lipids; according to the 2019 consensus redefinition, within the first 6 hours after transfusion, there is acute hypoxemia (PaO2/FiO2 ratio of 300 mmHg or below, or SpO2 below 90% in room air), bilateral pulmonary edema on imaging, and either no left atrial hypertension or left atrial hypertension that is not the main cause of hypoxemia.

This redefinition has removed the previous term 'possible TRALI' and divided TRALI into two types: the condition in a patient without ARDS risk factors is Type I, while the condition in a patient with an existing ARDS risk factor or on the background of mild ARDS (PaO2/FiO2 200-300) whose breathing worsens due to transfusion is classified as Type II; now the presence of an ARDS risk factor does not exclude a TRALI diagnosis. TACO, on the other hand, is hydrostatic (cardiogenic) volume overload; according to the 2018 revised surveillance definition, at least three of the following criteria must be met within 12 hours after transfusion: respiratory distress, signs of acute pulmonary edema, cardiovascular changes (tachycardia, hypertension, jugular venous distension), evidence of fluid overload, and elevated BNP/NT-proBNP.

Bacterial contamination and sepsis are particularly seen in platelet products stored at room temperature; bacterial contamination is detected in about one in every 1000-2500 platelet units, and the condition presents with high fever, rigor, and hypotension; in erythrocyte suspensions, Yersinia enterocolitica, which can grow in cold, is rare but a severe factor. TRALI and TACO are the leading causes of transfusion-related deaths in developed countries.

In laboratory diagnosis, low haptoglobin is a very sensitive marker for hemolysis; the direct antiglobulin (Coombs) test becomes positive in a hemolytic reaction, but if antibody coating is low density or transient, it may remain falsely negative, which can delay diagnosis.

Key considerations

• Differentiating TRALI from TACO is the most critical because although both cause dyspnea, hypoxia, and bilateral lung infiltrates within 6 hours after transfusion, their treatments are opposite: TRALI is a non-cardiogenic permeability edema, presents with normal or low filling pressures, unresponsiveness to diuretics, and generally normal BNP; TACO, on the other hand, is hydrostatic overload, presents with hypertension, jugular venous distension, increased BNP/NT-proBNP, positive fluid balance, and rapid response to diuretics; this distinction is vital as in TRALI, diuretics should be avoided.
• Both acute hemolytic reaction and bacterial septic reaction cause fever, rigor, and hypotension; hemolytic reaction is distinguished by hemoglobinuria, positive direct antiglobulin test, low haptoglobin, and elevated lactate dehydrogenase and bilirubin, while septic reaction is suggested by fever developing immediately after transfusion along with positive patient and unit cultures.
• Febrile non-hemolytic reaction is a diagnosis of exclusion; isolated fever should only be attributed to this diagnosis after acute hemolytic reaction and bacterial contamination have been safely excluded, because all three can start with the same early fever sign.
• The finding that differentiates an anaphylactic reaction from simple vasovagal syncope and other causes of dyspnea is the combination of hypotension with bronchospasm, stridor, angioedema, and widespread urticaria; isolated temporary urticaria is not anaphylaxis but a mild allergic reaction and does not worsen the clinical picture.
• The distinction between mild allergic reaction and anaphylactic reaction determines management; in the mild reaction, only skin findings (urticaria, itching) are present and transfusion can be continued slowly, whereas in anaphylaxis, respiratory, circulatory, or gastrointestinal involvement occurs and intramuscular adrenaline is required.
• Delayed hemolytic reaction, unlike the acute picture, appears days to weeks after transfusion with hemoglobin drop, mild jaundice, and positive antibody screening; it should be considered not in the first 24 hours, but when post-discharge hemoglobin remains lower than expected.
• Acute events independent of transfusion can occur simultaneously with the reaction; underlying sepsis, pulmonary thromboembolism, acute coronary syndrome, or a reaction due to another drug can mimic the same picture of fever, dyspnea, and hypotension, leading to the error of attributing it to transfusion.
• Hypotensive transfusion reaction is a distinct entity that occurs with isolated and usually transient low blood pressure; passing the product through a bedside negatively charged leukocyte filter generates bradykinin-like vasoactive peptides in blood components within a few minutes, and in a patient using an angiotensin-converting enzyme inhibitor, the breakdown of these peptides is already slowed, making the blood pressure drop more pronounced; unlike anaphylaxis, there are no accompanying skin, respiratory, or gastrointestinal symptoms, and it quickly resolves when the transfusion is stopped. Prestorage leukoreduction is preferred for prevention because bradykinin is degraded during storage; if the ACE inhibitor cannot be discontinued, a washed cellular product can be used.

Why it matters

The universal first step (stop the transfusion, keep the intravenous line open with 0.9% NaCl, check identity and label, retain the unit) both stops ongoing exposure to antigens and contaminants and catches clerical errors early; the British Society for Haematology 2023 guideline recommends starting treatment for severe reactions based on symptoms and signs without waiting for laboratory results. This check saves lives because a significant portion of ABO-incompatible transfusions result from identification errors; in UK hemovigilance data, about 13% of wrong blood in tube errors led to ABO-incompatible transfusion, and electronic patient identification during sampling has reduced these errors approximately fivefold compared to manual identification.

In acute hemolysis, maintaining urine flow with aggressive hydration (approximately 100 mL/hour or at least 1-2 mL/kg/hour) reduces acute tubular injury and pigment nephropathy caused by free hemoglobin and immune complexes; high-dose vasopressors that reduce renal perfusion are avoided. Adrenaline is the first-line treatment in anaphylaxis because it simultaneously provides vasoconstriction, bronchodilation, and suppression of mediator release; antihistamines and steroids are only auxiliary and should not delay adrenaline.

Since TRALI is a permeability (non-cardiogenic) edema, treatment is supportive and diuretics are harmful because they increase hypovolemia and hypotension; on the other hand, since TACO is a hydrostatic overload, slowing or stopping the transfusion and giving diuretics is essential, which is why distinguishing the two is critical. The strongest evidence in preventing TRALI is donor-related: the strategy of collecting plasma products primarily from male donors has reduced plasma-related TRALI from around 20 cases per million units to below 4, and in some centers, reduced total TRALI incidence by approximately 68%.

In bacterial contamination, early cultures (both patient and unit) and broad-spectrum intravenous antibiotics without delay are necessary to prevent high-fatality septic shock; storing platelets at room temperature significantly increases the risk. Febrile non-hemolytic reaction is a diagnosis of exclusion; this diagnosis should not be assumed at the first fever without excluding hemolysis and sepsis.

An abandoned doctrine is routinely giving premedication with paracetamol and diphenhydramine to all patients before transfusion; randomized studies have shown that this practice is ineffective in preventing febrile and allergic reactions, and since it carries harms such as falls, cognitive impairment, and liver toxicity, it is no longer recommended in patients without a prior history of reactions.

Critical complications

• Acute kidney injury is the most feared complication of acute hemolytic reaction; it is recognized by pigment nephropathy from free hemoglobin and immune complexes, manifests with oliguria and rising creatinine, is managed with aggressive hydration and maintenance of urine flow, and early renal replacement therapy is required in oliguric cases unresponsive to diuretics.
• Disseminated intravascular coagulation is a complication triggered by severe intravascular hemolysis; it is recognized by widespread leakage-bleeding, falling fibrinogen, prolonged prothrombin and activated partial thromboplastin time, and increased D-dimer, and is managed by stopping the underlying hemolysis and providing targeted blood product support (fresh frozen plasma, fibrinogen, platelets).
• Septic shock is the most severe course of bacterial contamination; Immediately following transfusion, it is recognized by high fever, rigor and resistant hypotension, managed without delay with broad-spectrum antibiotic, fluid resuscitation and vasopressor where necessary, all products produced from the same donation are quarantined.
• Respiratory failure is a common consequence of both TRALI and TACO; Recognized with progressive hypoxemia and increased respiratory work, managed by oxygen and, if necessary, non-invasive or invasive ventilation, but indiscriminate fluid withdrawal can be fatal, as the decision of diuretics is opposite in the two tables (essential in TACO, harmful in TRALI).
• Biphasic anaphylaxis is the recurrence of symptoms hours after the initial picture has resolved; Initially, it is recognized by the return of bronchospasm, hypotension or urticaria in the recovered patient, so after anaphylaxis, the patient is kept under observation for a while and ready for adrenaline again.
• Iatrogenic volume load and pulmonary edema develop as TACO due to overly rapid or multiple unit delivery; Dyspnea is recognized by hypertension and jugular fullness, managed by slowing transfusion, upright sitting and diuretics, and prevented by per-unit administration and slow infusion in the at-risk patient.
• Hypovolemia and hypotension due to excessive diuretic administration is an iatrogenic complication caused by the mistaking of TRALI for TACO and administering a diuretic; Recognized by reduced filling pressure and worsening perfusion, managed by discontinuation of the diuretic and careful fluid support, prevented by correct TRALI-TACO separation.
• Hypocalcemia due to citrate toxicity is a complication of massive transfusion given rapidly and in large numbers; It is caused by the citrate in the product binding ionized calcium and is recognized as hypotension with tetany, prolonged QT interval, decreased myocardial contractility; ionized calcium is measured frequently and managed with intravenous calcium replacement, the goal in patients with massive bleeding is to keep it close to the upper limit of the normal range.
• Hyperkalemia develops in massive transfusion, which is given particularly rapidly and in large numbers, due to the accumulation of extracellular potassium due to loss of function of cell membrane adenosine triphosphatase pumps in the stored erythrocyte suspension; recognized by spike T waves and arrhythmia on electrocardiography, managed with calcium gluconate, insulin-glucose, and, if necessary, dialysis.

Special considerations

• Plasma-containing products are of particular importance regarding TRALI in pregnant and postpartum patients; since the frequency of anti-leukocyte antibodies is high in the plasma of female donors with a history of pregnancy, the risk of TRALI increases, and therefore plasma is given predominantly from male donors in most countries; moreover, since physiological hypervolemia already exists in pregnant women, the threshold for TACO is low and the transfusion rate is adjusted accordingly.
• In newborns and infants, TACO develops much more easily because circulating blood volume is small; since they can become overloaded even with small volume increases, the transfusion volume is calculated per kilogram and administered slowly. Additionally, since febrile non-hemolytic reaction may not be reliably measurable in this group, fever is always evaluated together with hemolysis and sepsis.
• In elderly patients, TACO is the most important risk; due to reduced cardiac and renal reserve, rapid or multiple units can trigger decompensated heart failure, so slow infusion, re-evaluation per unit, and prophylactic diuretics in high-risk cases are applied.
• In patients with renal failure, TACO risk increases because their capacity to tolerate fluid load is low, and in acute hemolytic reaction, the already damaged kidney progresses more rapidly to oliguria. Hydration targets are carefully titrated by monitoring volume status, and the need for dialysis is assessed early.
• Immunosuppressed patients and hematopoietic stem cell recipients carry the risk of transfusion-associated graft-versus-host disease; to prevent this fatal complication, cellular blood products are given irradiated. Additionally, since fever response may be suppressed in this group, bacterial contamination may present atypically and with delay.
• In patients with known IgA deficiency and anti-IgA antibodies who have a history of anaphylaxis, subsequent transfusions are performed with washed red cells and platelets or IgA-deficient donor products; since plasma cannot be washed, if plasma is needed, it must be obtained from an IgA-deficient donor.
• Erythrocyte alloimmunization occurs much more frequently in patients with sickle cell disease who receive repeated transfusions compared to the general transfusion population (approximately 18-37%, versus 2-5% in the general population), and delayed hemolytic reaction can develop on this alloimmunization background; in this scenario, both the transfused and the patient's own erythrocytes are destroyed, hemoglobin drops below pre-transfusion levels, and usually within 24 hours to 28 days after transfusion (typically about a week later), it often goes unnoticed, mimicking a painful vaso-occlusive crisis with back/leg/abdominal pain, fever, and hemoglobinuria; additional erythrocyte transfusion in this patient is usually AVOIDED as it may exacerbate hemolysis, and supportive therapy along with an immunomodulatory approach is preferred.

Follow-up plan

In each reaction, start a transfusion reaction investigation: post-transfusion blood sample + urine sample + remaining unit/set to the blood bank; identity/compatibility is re-verified. In suspected hemolytic reaction: monitor DAT (direct Coombs), plasma/urine free hemoglobin, haptoglobin, LDH, indirect bilirubin, peripheral smear, complete blood count, renal function, and coagulation (for DIC, fibrinogen/D-dimer/PT-aPTT); urine output and renal function are closely monitored for at least 24 hours, unresponsive oliguria is evaluated by nephrology/dialysis.

In septic reaction, follow cultures/Gram results from the patient and unit, narrow antibiotics; the blood bank quarantines other products from the same donation. In TRALI/TACO, monitor respiratory status, oxygenation, and (for TACO) fluid balance/BNP; radiological improvement is followed.

After anaphylaxis, observe for biphasic reactions and document a plan for washed/IgA-deficient products for future transfusions. ALL reactions are reported to the institutional hemovigilance system.

In recurrent febrile/allergic reactions, a leukocyte-reduced product strategy is recorded; however, routine premedication is not recommended for a patient with no prior history of reactions, because randomized studies have shown it to be ineffective in preventing reactions. Before discharge, the patient is told to return if unexplained jaundice, dark urine, or lower-than-expected hemoglobin develops in the following days, for consideration of delayed hemolytic reaction; a patient who experienced anaphylaxis is advised to stay until the observation period is completed due to the risk of biphasic reaction and to carry a document indicating the need for special products in future transfusions.

The frequency of follow-up is determined according to the type of reaction: in severe hemolytic or septic reactions, vital signs, urine output, and laboratory tests are monitored at short intervals for at least the first 24 hours, and in respiratory reactions, oxygenation and radiology are followed until normalization. In the long term, most TRALI cases resolve without sequelae within 24-96 hours; in contrast, acute kidney injury due to severe hemolytic reaction may require temporary dialysis, and renal function is re-evaluated over weeks.