The impact of iron store on red blood cell transfusion: a multicentre prospective cohort study in cardiac surgery

Background: Anaemia is common prior to cardiac surgery and contributes to perioperative morbidity. Iron deficiency is the main cause of anaemia but its impact remains controversial in the surgical setting. We aimed to estimate the impact of iron deficiency on in-hospital perioperative red blood cell transfusion for patients undergoing elective and urgent cardiac surgery. Secondary objectives were to identify risk factors associated with in-hospital red blood cell transfusion. Methods: We conducted a prospective multicentre observational study in three university hospitals performing cardiac surgery. We determined iron status prior to surgery and collected all transfusion data to compare iron-deficient and iron-replete patients during hospital stay. We performed a multivariable logistic regression to compare transfusion among groups. Results: Five hundred and two patients were included. A trend of low haemoglobin levels associated with iron deficiency persisted until discharge. Red blood cell transfusion was significantly higher in the group of iron deficient patients during surgery (22% vs 13%, p= 0.017), however the incidence during the whole hospital stay was 31% in the iron-deficient group, not significantly different with the non-deficient group (26%, p= 0.28). Iron deficiency was not independently associated with in-hospital red blood cell transfusion (adjusted OR = 0.85 [0.53-1.36], p= 0.49). Conclusions: In-hospital red blood cell transfusion was not significantly higher in iron-deficient patients and iron deficiency was not associated with in-hospital red blood cell transfusion in patients undergoing elective and urgent cardiac surgery. Iron deficiency was the main cause of anaemia and anaemia was a strong driver of red blood cell transfusion. Further studies should identify sub-population of iron-deficient patients which may benefit from preoperative iron deficiency management and explore the long-term impact of lower haemoglobin levels at discharge in the iron deficient population.