TACO vs TRALI Interpreter
TACO vs TRALI Interpreter
Both present as hypoxia during or after a transfusion, and telling them apart changes the treatment completely. Work through the discriminators the 2019 TRALI consensus and the revised ISBT TACO definition actually use — timing, fluid balance, blood pressure, natriuretic peptide, diuresis and ARDS risk factors.
TACO or TRALI
Six discriminatorsA patient with non-pulmonary sepsis becomes hypoxic three hours after a red cell transfusion. Blood pressure has fallen, fluid balance is clearly positive with weight gain, the natriuretic peptide is raised and more than 1.5× the pre-transfusion value, and there is no improvement after diuresis
The discriminators, and where each one comes from
Mechanism — “In TRALI, the primary physiologic abnormality resulting in pulmonary edema is an increase in capillary permeability, while in TACO, edema is believed to result primarily from increased capillary hydrostatic pressure (nonpermeability edema).”
Everything below follows from that one sentence.
- blood pressure
- TACO typically raises it, with a widened pulse pressure — it is listed among the cardiovascular changes in criterion C. TRALI typically lowers it. Not decisive alone: a failing ventricle can make TACO hypotensive
- fluid balance
- criterion D of the TACO definition — “a positive fluid balance; response to diuretic therapy” and a change in weight. TRALI is a leak, not a load, so the balance is usually neutral
- natriuretic peptide
- criterion E — above the age-specific reference range AND more than 1.5 times the pre-transfusion value. The 1.5-fold clause is why a stored pre-transfusion sample is worth having. The definition also states that “A normal post-transfusion NP level is not consistent with a diagnosis of TACO”, which makes a normal result a genuine exclusion rather than a weak argument. See the NT-proBNP unit converter if the pre- and post-transfusion results are in different units
- response to diuresis
- a hydrostatic oedema unloads when the volume comes off; a permeability oedema does not. It is part of criterion D and it is one of the most informative things available at the bedside
- ARDS risk factors
- the consensus panel’s own list — direct: pneumonia, aspiration of gastric contents, inhalational injury, pulmonary contusion, pulmonary vasculitis, drowning; indirect: non-pulmonary sepsis, major trauma, pancreatitis, severe burns, non-cardiogenic shock, drug overdose. Their presence does not exclude TRALI, it makes it Type II
- the two scores on this page
- counts of the features above, used only to order the rules. They are not a published score and no threshold on them has been validated. The definitions are criterion counts, not weighted scores, and the verdict text always names which criteria are and are not met
Worked example
A patient with non-pulmonary sepsis becomes hypoxic three hours after a red cell transfusion. Blood pressure has fallen, fluid balance is clearly positive with weight gain, the natriuretic peptide is raised and more than 1.5× the pre-transfusion value, and there is no improvement after diuresis
Three hours, so inside both windows — TRALI's 6 hours and TACO's 12. Timing settles nothing here
TACO-ward features: positive fluid balance (criterion D) and a raised natriuretic peptide above the reference range and over 1.5× baseline (criterion E) → 2
TRALI-ward features: blood pressure fallen, and no improvement after diuresis, which a hydrostatic oedema would not do → 2
Sepsis is an indirect ARDS risk factor from the consensus panel's own list, so if this were TRALI it would be Type II — which requires that the respiratory status was stable in the 12 hours before the transfusion
Two against two. The honest answer is the one the panel provided a category for: TRALI/TACO cannot be distinguished
That is not an evasion. Both are treated with oxygen and respiratory support; diuresis is given cautiously and reassessed rather than committed to; further transfusion stops until the picture clarifies; and the case is reported as undistinguished
Change one input — set the diuresis response to "clear improvement" — and the verdict becomes TACO. Change the fluid balance to neutral and the natriuretic peptide to normal instead, and it becomes TRALI Type II. Both changes are single observations, and both are things somebody has to go and find out
Side by side
| TACO | TRALI | |
|---|---|---|
| Mechanism | Raised capillary hydrostatic pressure — a volume the circulation cannot accommodate | Increased capillary permeability — donor antibodies or biologically active lipids injuring the pulmonary endothelium |
| Window | During, or up to 12 hours after transfusion | During, or within 6 hours; usually within 2 |
| Blood pressure | Usually raised, often with a widened pulse pressure | Usually fallen |
| Fluid balance | Clearly positive, with weight gain, raised JVP, peripheral oedema | Neutral — this is a leak, not a load |
| Natriuretic peptide | Above the age-specific reference range and more than 1.5× the pre-transfusion value | Normal. A normal post-transfusion level “is not consistent with a diagnosis of TACO” |
| Response to diuresis | Improves | Does not improve, and fluid restriction may harm |
| ARDS risk factors | Not part of the definition | Absent → Type I. Present, or mild pre-existing ARDS, with a stable respiratory status in the previous 12 hours → Type II |
| Treatment | Sit up, oxygen, stop the transfusion and any fluid, diuretic | Oxygen and respiratory support. Supportive only — not a diuretic |
| Prevention | Weight-adjusted dosing, single-unit transfusion in chronic anaemia, prophylactic diuretic in high-risk patients, review after each unit | Donor deferral — male-predominant or antibody-tested plasma, and deferral of implicated donors |
What haemovigilance actually counts
| Reported to SHOT | |
|---|---|
| Total transfusion-related deaths, 2024 | “The number of reported deaths assessed as being related to the transfusion increased dramatically to 59 in 2024, from 38 in 2023” |
| TACO deaths, 2024 | 31 — more than half of all transfusion-related deaths that year, and the single largest category |
| TACO cases, 2024 | “The number of cases reported in 2024 (n=188) is the highest to date and is an increase of 16 cases from 2023” |
| Preventability | “46/188 (24.5%) of TACO cases had evidence of unnecessary/avoidable, or excessive volume of transfusion”, including 6 of the 31 deaths |
| Pulmonary complications and delays together | “53/59 (89.8%) of total deaths” |
| TRALI, for comparison | 3 confirmed antibody-positive cases and 0 related deaths in the reporting year quoted |
The famous one and the one that kills
TRALI is the transfusion reaction everyone has heard of. It was the leading cause of transfusion-related death for years, it generated a large literature, and blood services changed their donor policies because of it — moving to male-predominant or antibody-tested plasma, and deferring donors implicated in cases — with the result that its incidence fell sharply. TACO did not fall, and the two have swapped places. In the 2024 Annual SHOT Report the number of transfusion-related deaths rose to 59, and 31 of them were transfusion-associated circulatory overload: more than half of every transfusion-related death in the scheme that year, and the largest single category by a wide margin. The reported case count, 188, was the highest ever recorded. In the same reporting period TRALI accounted for a handful of confirmed antibody-positive cases and no deaths. The reaction with the smaller reputation is doing almost all of the killing, and it is the more preventable of the two: SHOT found evidence of unnecessary, avoidable or excessive-volume transfusion in a quarter of TACO cases, including six of the deaths. That is the fact that makes this page worth reading.
They are hard to tell apart because they look the same from the end of the bed. Both produce acute hypoxia and bilateral pulmonary infiltrates within hours of a transfusion, and neither has a diagnostic test. What separates them is mechanism, and one sentence from the 2019 consensus panel does all the work: “In TRALI, the primary physiologic abnormality resulting in pulmonary edema is an increase in capillary permeability, while in TACO, edema is believed to result primarily from increased capillary hydrostatic pressure (nonpermeability edema).” Everything downstream follows. A hydrostatic oedema comes with the signs of a loaded circulation — a positive fluid balance, weight gain, a raised jugular venous pressure, a rising blood pressure and widened pulse pressure, a natriuretic peptide that climbs above the reference range and to more than one and a half times its pre-transfusion value — and it unloads when you take the volume off. A permeability oedema comes with none of those, tends to drop the blood pressure rather than raise it, leaves the natriuretic peptide alone, and does not respond to diuresis; treating it with fluid restriction can make things worse.
The natriuretic peptide deserves particular attention because it is the one laboratory discriminator in either definition, and because it is usually used wrongly. Criterion E of the revised TACO definition is not “a raised BNP”. It is an increase above the age-specific reference range and to more than 1.5 times the pre-transfusion value — which means the pre-transfusion sample is the load-bearing one, and a hospital that keeps a sample before transfusing high-risk patients can answer a question afterwards that no amount of post-transfusion testing will settle. The definition also makes the negative claim explicitly: “A normal post-transfusion NP level is not consistent with a diagnosis of TACO.” That makes a normal result a genuine exclusion rather than a weak argument, and it is the single most useful thing to measure in a patient who became hypoxic after a transfusion. If the two results are reported in different units, the NT-proBNP unit converter will line them up.
Two honesties belong on any page about this. The first is TRALI Type II. The 2019 redefinition split TRALI in two: Type I is the patient with no ARDS risk factor, and Type II is the patient who has one — pneumonia, aspiration, inhalational injury, pulmonary contusion, pulmonary vasculitis, drowning, non-pulmonary sepsis, major trauma, pancreatitis, severe burns, non-cardiogenic shock or drug overdose — or mild pre-existing ARDS, whose respiratory status was stable in the 12 hours before the transfusion and then deteriorated. Before that split, those patients were quietly written off as deteriorating from their underlying illness, and their transfusions were never examined. The presence of a risk factor does not exclude TRALI; it decides which type you report. The second honesty is that sometimes there is no answer. A patient can be volume-overloaded and have a permeability injury at the same time, and the consensus classification includes categories both for TRALI and TACO occurring concurrently and for cases where TRALI and TACO cannot be distinguished. The panel even accepted that some degree of left atrial hypertension may be present and the case still be classified as TRALI, if inflammatory oedema predominates. When the features split down the middle — as this page’s own default inputs do — the right thing is to support the patient in the way both conditions need, be cautious rather than committed with diuresis, stop transfusing until the picture clarifies, and report the case as undistinguished rather than guessing.
Frequently asked questions
How do you tell TACO from TRALI at the bedside?
Six things, and none of them alone. Timing: TRALI must begin during or within 6 hours of the transfusion, TACO within 12. Blood pressure: TACO usually raises it with a widened pulse pressure, TRALI usually lowers it. Fluid balance: clearly positive with weight gain and a raised JVP in TACO, neutral in TRALI. Natriuretic peptide: raised above the reference range and to more than 1.5 times the pre-transfusion value in TACO, normal in TRALI — and a normal post-transfusion level is stated by the TACO definition to be inconsistent with TACO. Response to diuresis: TACO improves, TRALI does not. And ARDS risk factors, which do not decide between them but decide whether TRALI is Type I or Type II.
Is TACO really more dangerous than TRALI?
In current haemovigilance data, yes, by a wide margin. The 2024 Annual SHOT Report recorded 59 transfusion-related deaths, of which 31 were TACO — more than half of all of them and the largest single category — against a handful of confirmed antibody-positive TRALI cases and no TRALI deaths in the reporting year quoted. TACO case reports in 2024 were the highest on record at 188. The reversal is not because TACO became more dangerous but because TRALI became much rarer: blood services changed plasma sourcing to male-predominant or antibody-tested donations and deferred implicated donors. Nothing equivalent was done about volume, and TACO is substantially preventable — SHOT found unnecessary, avoidable or excessive-volume transfusion in a quarter of its TACO cases.
What is TRALI Type II?
The 2019 consensus redefinition divided TRALI into two types. Type I applies to patients with no risk factors for ARDS. Type II applies to patients who have an ARDS risk factor, or who have existing mild ARDS with a P/F ratio of 200–300, but whose respiratory status deteriorates and is judged to be due to the transfusion — and the defining requirement is that the respiratory status was stable in the 12 hours before the transfusion. The point of the category is that having pneumonia, sepsis or major trauma does not protect you from TRALI, and before the split those patients’ deteriorations were attributed to their underlying illness and never investigated. Management is identical to Type I: supportive, not diuretic.
Can a patient have both TACO and TRALI?
Yes, and the surveillance system is built to say so. The 2019 consensus classification includes a category for TRALI and TACO occurring concurrently in the same patient, and another for cases where TRALI and TACO cannot be distinguished. The panel also allowed that some degree of left atrial hypertension may be present and a case still be classified as TRALI, where inflammatory permeability oedema is judged to predominate. Practically, a coexisting or undistinguished case gets oxygen and respiratory support, cautious rather than committed diuresis with reassessment, no further transfusion until things clarify, and an honest report. Haemovigilance schemes would much rather receive “cannot distinguish” than a confident wrong label.
How is the natriuretic peptide used in the TACO definition?
Criterion E requires the post-transfusion level to be above the age-group-specific reference range AND greater than 1.5 times the pre-transfusion value. Both halves matter: many hospital inpatients have a chronically raised natriuretic peptide, so an absolute value on its own settles nothing, and the ratio is what identifies an acute change. That makes the pre-transfusion sample the valuable one, and keeping a sample before transfusing a high-risk patient answers a question that post-transfusion testing alone cannot. The definition also states that a normal post-transfusion level is not consistent with a diagnosis of TACO, which turns a normal result into a real exclusion. If the two results come back in different units, convert them before comparing.
Related calculators
References
- Vlaar APJ, Toy P, Fung M, et al. A consensus redefinition of transfusion-related acute lung injury. Transfusion. 2019;59(7):2465–2476. TRALI Type I — no ARDS risk factors, acute onset, hypoxaemia (P/F ≤ 300 or SpO₂ < 90% on room air), clear evidence of bilateral pulmonary oedema on imaging, no evidence of left atrial hypertension or, if present, judged not to be the main contributor, onset during or within 6 hours of transfusion, no temporal relationship to an alternative ARDS risk factor. Type II — ARDS risk factors or existing mild ARDS (P/F 200–300) with deterioration judged due to transfusion, the Type I findings, and a stable respiratory status in the 12 hours before transfusion. Classification categories include concurrent TRALI and TACO, and "TRALI/TACO cannot be distinguished".
- Wiersum-Osselton JC, Whitaker B, Grey S, et al. Revised international surveillance case definition of transfusion-associated circulatory overload: a classification agreement validation study. Lancet Haematol. 2019;6(7):e350–e358. Acute or worsening respiratory compromise and/or evidence of pulmonary oedema during or up to 12 hours after transfusion, with a total of three or more criteria: (A) acute or worsening respiratory compromise; (B) evidence of acute or worsening pulmonary oedema on clinical examination and/or imaging; (C) cardiovascular changes — tachycardia, hypertension, widened pulse pressure, jugular venous distension, enlarged cardiac silhouette and/or peripheral oedema; (D) evidence of fluid overload — positive fluid balance, response to diuretic therapy, change in weight; (E) an increase in B-type natriuretic peptide above the age-group-specific reference range and greater than 1.5 times the pre-transfusion value. “A normal post-transfusion NP level is not consistent with a diagnosis of TACO.”
- Serious Hazards of Transfusion (SHOT). Annual SHOT Report 2024, Headline Data chapter. “The number of reported deaths assessed as being related to the transfusion increased dramatically to 59 in 2024, from 38 in 2023”; 31 of those deaths were TACO; “Pulmonary complications and transfusion delays were still the most common causes of transfusion-related deaths reported to SHOT in 2024, accounting for 53/59 (89.8%) of total deaths.”
- Serious Hazards of Transfusion (SHOT). Annual SHOT Report 2024, Transfusion-Associated Circulatory Overload chapter. “The number of cases reported in 2024 (n=188) is the highest to date and is an increase of 16 cases from 2023”; “46/188 (24.5%) of TACO cases had evidence of unnecessary/avoidable, or excessive volume of transfusion”, including 6 of the 31 deaths. Risk assessment covers heart failure, diuretic use, severe anaemia, pulmonary oedema, respiratory symptoms, positive fluid balance, concurrent intravenous fluids, peripheral oedema, low serum albumin and renal impairment; mitigation includes weight-based dosing, single-unit transfusion in chronic anaemia, diuretic consideration and clinical review after each unit.
- Tinegate H, Birchall J, Gray A, et al. Guideline on the investigation and management of acute transfusion reactions. British Committee for Standards in Haematology; Br J Haematol. 2012;159(2):143–153. TRALI: during or within 6 hours of transfusion, usually within 2 hours, with reduced blood pressure, a normal JVP and a normal echocardiogram. TACO: dyspnoea, typically in patients over 70, with raised blood pressure, raised JVP and cardiomegaly on imaging.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.