Summary
A preprint meta-analysis of 14 observational studies found that preoperative anaemia was associated with higher odds of transfusion, kidney complications, early mortality and infection after adult cardiac surgery. The authors report low or very low certainty for these findings and say the observational evidence cannot establish causation.
A systematic review and meta-analysis of 14 observational studies, covering 74,571 adults undergoing cardiac surgery, found that preoperative anaemia was associated with higher odds of several postoperative complications. The preprint reports associations with red-cell transfusion, kidney injury or renal failure, early mortality and infection; it found no clear association with postoperative stroke. The authors caution that observational data cannot establish that anaemia caused these outcomes.
What the review found
The included studies reported 17,349 patients with preoperative anaemia, or 23.3% of the total. In the pooled analyses, anaemia was associated with an odds ratio (OR) of 3.66 for red-cell transfusion (95% confidence interval [CI], 2.14–6.24), 2.43 for acute kidney injury or renal failure (95% CI, 1.84–3.21), 2.11 for early mortality (95% CI, 1.40–3.17) and 1.49 for postoperative infection (95% CI, 1.21–1.82).
An odds ratio compares the odds of an outcome between groups; it is not a direct measure of how much an individual patient’s probability of that outcome changes. The review reported no clear association with postoperative stroke: OR 1.16, with a 95% CI from 0.43 to 3.17. That interval includes no difference and spans a wide range of possible associations.
The authors rated certainty as low for renal outcomes and very low for the other outcomes. The review’s findings therefore indicate patterns in the available studies, with greater uncertainty around how precisely they describe the underlying associations.
How the evidence was assembled
The authors searched five databases for peer-reviewed English-language studies published from 2017 through July 2026. They report following PRISMA 2020 and using random-effects meta-analysis, with restricted maximum likelihood estimation and Hartung–Knapp confidence intervals. Crude estimates from event counts were the main analysis; adjusted estimates were analysed separately.
Because all 14 included studies were observational cohorts, the results show that anaemia and these outcomes occurred together more often in the reported data, not that one necessarily produced the other. Anaemia may be a useful marker of perioperative risk, as the authors conclude, but this review does not test whether treating it before surgery changes outcomes. The report is a medRxiv preprint.