This is a plain English summary of an original research article
This large NIHR-funded randomised trial found that using a lower haemoglobin threshold was no better or cheaper than using a higher one when deciding to transfuse blood after non-emergency cardiac surgery.
People with milder anaemia, receiving blood transfusion at a haemoglobin level less than 90g/L (the liberal transfusion group) had similar health outcomes and health costs in the three months after surgery, compared with those only given a transfusion when they developed more severe anaemia at a threshold less than 75g/L (the restricted transfusion group).
However, more deaths were recorded in the restricted group. Doctors may need to review recommended transfusion practice after cardiac surgery.
Why was this study needed?
Existing research has shown conflicting results on the benefits and harms of blood transfusion to manage post-operative anaemia. Observational studies have shown associations between liberal use of blood transfusion and higher infection risk, while clinical trials have suggested that it is safe to use a lower haemoglobin value as the threshold trigger for blood transfusion. However, the few studies that involved planned cardiac surgery found that there was no difference in health outcomes or cost for different blood transfusion thresholds.
Uncertainty about which threshold to use is mirrored in practice; national, regional and local audits in England consistently show inappropriate variation in use of all blood components. To investigate the issue, the NIHR funded the Transfusion Indication Threshold Reduction (TITRe2) trial to compare a liberal blood transfusion threshold of less than 90g/L with a restrictive threshold of less than 75g/L.
What did this study do?
This randomised controlled trial assigned 2,003 patients from 17 UK centres to either a liberal (90g/L) or a restricted (75g/L) transfusion threshold. These levels acted as post-operative triggers for receiving successive units of red blood cells until the recipient’s haemoglobin was above the threshold. Assignment to groups happened when haemoglobin dropped below 90g/L. The main outcome was a major infection or ischaemic event (loss of blood supply to an organ). The trial was well designed and implemented.
Cost analysis included costs of tests, blood products and hospital stay, but not the cardiac operation itself, which would have varied by condition.
What did it find?
- There was no difference between the groups in the number of patients who experienced the main outcome. A serious infection or ischaemic event occurred in 35.1% of the patients in the restrictive group and 33.0% of the patients in the liberal group (odds ratio, 1.11 95% Confidence Interval[CI] 0.91 to 1.34)
- 4.2% of participants had died after three months in the restricted threshold group, compared to 2.6% in the liberal threshold group (Hazard ratio 1.64, 95% CI 1.00 to 2.67; p=0.045). As this result was a secondary outcome, and the confidence intervals include the possibility that mortality is the same in the two groups, this result should be interpreted cautiously
- Total mean costs three months after surgery were similar between the groups: £10,636 in the restrictive group compared with £10,814 in the liberal group.
What does current guidance say on this issue?
While the final decision to authorise a blood transfusion rests on clinical judgement, the Joint UK Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee (JPAC) and The American Association of Blood Banks (AABB) guidelines recommend using restrictive thresholds after cardiac surgery. They state that transfusion should be considered at haemoglobin levels less than 80g/L and are usually indicated at levels less than 70g/L.
At the health service management level, the UK National Blood Transfusion Committee recommends the use of locally agreed triggers for transfusion based on national guidelines. They also recommend the development of systems and protocols that empower laboratory staff to question requests that do not conform to the agreed triggers, and regular local audits of transfusion requests.
What are the implications?
The TITRe2 trial findings challenge current guideline recommendations from the JPAC and AABB. The current recommendations to use restricted transfusion thresholds after cardiac surgery may not be supported by this evidence on effectiveness and cost effectiveness.
The TITRe2 trial differed from earlier large trials of transfusion thresholds in that all the participants had cardiovascular disease. Some of the participants may therefore have been at the limits of their cardiovascular reserve, meaning that their heart was already near its maximum capacity for pumping blood. Such participants may have benefited more from the higher haemoglobin levels compared to participants in other trials without cardiovascular disease. Because of this, the authors suggested that patients with cardiovascular disease may represent a specific high-risk group for whom more liberal transfusion thresholds are to be recommended. This suggestion could be tested in future trials.
Murphy GJ, Pike K, Rogers CA et al. Liberal or restrictive transfusion after cardiac surgery. New England Journal of Medicine. 2015;372:997-1008.
This project was funded by the National Institute for Health Research HTA Programme (project number 06/402/94).
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