Association Between Preoperative Anemia and Postoperative Outcomes in Adults Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

Q: What are the key findings of this study?

Preoperative anaemia was associated with significantly higher odds of early in-hospital or 30-day mortality (OR 2.11, 95% CI 1.40-3.17; p = 0.0036) in adults undergoing cardiac surgery.

Q: What is the clinical evidence from this study?

Study design: Meta-Analysis. Population: Adults undergoing cardiac surgery (n=74571). Intervention: Preoperative anaemia vs. Non-anaemic patients. Primary outcome: Early mortality (in-hospital or 30-day mortality) (OR 2.11, 95% CI 1.40-3.17, p=0.0036).

Q: What does this research mean for the field?

Preoperative anaemia in adults undergoing cardiac surgery is associated with more than double the odds of early mortality and acute kidney injury, as well as increased red blood cell transfusion and postoperative infection. Novelty: ClaimNovelty.SYNTHESIS. Consensus alignment: ConsensusAlignment.NEUTRAL.

Wesam Abedalqader Hammad; Abdalrahman A.I Hammad

doi:10.64898/2026.09.24.26363864

September 30, 2026Open Access

Association Between Preoperative Anemia and Postoperative Outcomes in Adults Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

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Key result

Preoperative anaemia is linked to ~2.1-fold higher early mortality after cardiac surgery.

OR 2.11
95% CI 1.40-3.17
P=0.0036
n=74,571

Why the study?

Preoperative anaemia is common in adults undergoing cardiac surgery and may identify patients at increased perioperative risk, prompting a synthesis of contemporary observational evidence on its association with postoperative outcomes.

Does preoperative anemia increase the risk of short-term mortality and major postoperative complications compared to no anemia in adults undergoing cardiac surgery?

Key Points

To assess the relationship between preoperative anemia and adverse postoperative outcomes among adult patients undergoing cardiac surgery.
Conducted a systematic review and meta-analysis adhering to PRISMA 2020 guidelines, searching five databases for observational studies published from 2017 to July 2026.
Identified 14 observational cohort studies including 74,571 adults (17,349 [23.3%] with preoperative anemia) undergoing cardiac surgery.
Synthesized data via random-effects meta-analyses using restricted maximum likelihood estimation with Hartung-Knapp confidence intervals.
Preoperative anemia was significantly associated with higher odds of early mortality (OR, 2.11; 95% CI, 1.40–3.17; p = 0.0036; 8 studies, n = 59,769) and red blood cell transfusion (61.1% vs 28.5%; OR, 3.66; 95% CI, 2.14–6.24; p < 0.001; 9 studies, n = 65,492).
Patients with anemia had higher odds of acute kidney injury or renal failure (OR, 2.43; 95% CI, 1.84–3.21; p < 0.001) and postoperative infection (OR, 1.49; 95% CI, 1.21–1.82; p = 0.0086).
No significant difference was observed for postoperative stroke between patients with and without anemia (OR, 1.16; 95% CI, 0.43–3.17; p = 0.6617).

Study Design

Type

Meta-Analysis (n=74,571)

Multicenter

Yes

Structured PICO

Does preoperative anemia increase the risk of short-term mortality and major postoperative complications compared to no anemia in adults undergoing cardiac surgery?

P

Population

74,571 adults aged ≥18 years undergoing cardiac surgery across 14 observational cohort studies, including 17,349 (23.3%) with preoperative anaemia, followed through index hospitalization or 30 days.

E

Exposure

Preoperative anemia (exposure defined by WHO sex-specific criteria [Hb <13.0 g/dL in men, <12.0 g/dL in non-pregnant women], study-specific hemoglobin thresholds, hematocrit thresholds, or ferritin levels).

C

Comparator

Non-anemic patients undergoing cardiac surgery (n=57,222).

O

Outcome

Short-term (early) mortality, defined as death within 30 days after cardiac surgery or during the index hospitalization.hard clinical

Main Result

Odds Ratio: 2.11 (95% CI 1.4–3.17)

p-value: p=0.0036

Preoperative anemia in adults undergoing cardiac surgery is strongly associated with more than double the odds of early mortality and acute kidney injury, and nearly quadruple the odds of red-cell transfusion, underscoring its value as a key perioperative risk marker.

Limitations

Observational nature of included studies prevents establishing causality and leaves residual confounding
Heterogeneity in definitions of preoperative anaemia across studies
Substantial statistical heterogeneity in several pooled outcomes (e.g., I² = 58.4% for early mortality, 70.1% for AKI, and 97.7% for transfusion)
Low to very low certainty of evidence on GRADE assessment
Small number of studies in several subgroup analyses and inability to perform funnel plots/Egger's test due to <10 studies per outcome
Observational nature of included studies prevents establishing causality and leaves potential for residual confounding
Clinical and statistical heterogeneity due to differing definitions of preoperative anemia (WHO criteria, study-specific hemoglobin/hematocrit thresholds, ferritin levels) across studies
Differing covariate adjustment sets, matching procedures, and modelling approaches across studies could not be reliably harmonized
Low certainty of evidence for renal outcomes and very low certainty for other outcomes according to GRADE assessment
Fewer than ten study estimates per outcome precluded funnel plots and Egger's test for publication bias

Implication

Preoperative anemia may refine mortality risk stratification before cardiac surgery; leaves open whether correction improves outcomes in randomized trials.

Abstract

Preoperative anaemia is common in adults undergoing cardiac surgery and may identify patients at increased perioperative risk. This systematic review and meta-analysis synthesised contemporary observational evidence in accordance with PRISMA 2020. Five databases were searched for peer-reviewed English language studies published from 2017 to July 2026. Random effects meta-analyses used restricted maximum likelihood estimation with Hartung-Knapp confidence intervals; crude exact count estimates were synthesised primarily and adjusted estimates separately. Fourteen observational cohort studies involving 74,571 adults, including 17,349 (23.3%) with anaemia, were included. Preoperative anaemia was associated with red cell transfusion (OR, 3.66; 95% CI, 2.14-6.24), acute kidney injury or renal failure (OR, 2.43; 95% CI, 1.84-3.21), early mortality (OR, 2.11; 95% CI, 1.40-3.17), and postoperative infection (OR, 1.49; 95% CI, 1.21-1.82), but not postoperative stroke (OR, 1.16; 95% CI, 0.43-3.17). Certainty was low for renal outcomes and very low for the other outcomes. Preoperative anaemia is an important perioperative risk marker, particularly for transfusion and renal complications, although causality cannot be established.

Discussion

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Cite This Study

Hammad et al. (2026) conducted a meta-analysis in Adults undergoing cardiac surgery (n=74,571). Preoperative anaemia vs. Non-anaemic patients was evaluated on Early mortality (in-hospital or 30-day mortality) (OR 2.11, 95% CI 1.40-3.17, p=0.0036). Preoperative anaemia was associated with significantly higher odds of early in-hospital or 30-day mortality (OR 2.11, 95% CI 1.40-3.17; p = 0.0036) in adults undergoing cardiac surgery.

synapsesocial.com/papers/6ae28dedcbadf70daf6c3fa8 https://doi.org/10.64898/2026.09.24.26363864

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Association Between Preoperative Anemia and Postoperative Outcomes in Adults Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

Association Between Preoperative Anemia and Postoperative Outcomes in Adults Undergoing Cardiac Surgery: A Systematic Review and Meta-analysis

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

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