Associations between non-anaemic iron deficiency and outcomes following elective cardiac surgery (IDOLS): a prospective cohort study

Background One in two adults undergoing cardiac surgery are iron deficient, best practice guidelines and consensus statements recommend routine investigation and treatment of iron deficiency before elective cardiac surgery, even in the absence of anaemia; however, it is not dear if non-anaemic iron deficiency is associated with worse outcomes in this patient population. We hypothesised that iron deficiency would be associated with worse postoperative outcomes than an iron replete state in adults without anaemia undergoing elective cardiac surgery. Methods We performed a prospective, cohort study at two hospitals in Australia. We recruited adults (ie, people 18 years and older) undergoing elective cardiac surgery without anaemia (defined as a haemoglobin of less than 130 g/L for men and less than 120 g/L for women), concomitant haemoglobinopathy, bone marrow pathology, haemochromatosis, or end-stage renal failure requiring dialysis. Participants were stratified as iron deficient or iron replete on the basis of preoperative testing. Iron deficiency was defined as a serum ferritin of less than 100 mu g/L or 100-300 mu g/L if transferrin saturation was less than 20% or C-reactive protein was more than 5 mg/L. The primary endpoint was days alive and at home at postoperative day 30. The primary analysis included all patients with data available for the primary endpoint and was adjusted for risk measured using EuroSCORE-II and body surface area. The study was prospectively registered with the Australian and New Zealand Clinical Trials Registry, ACTRN12618000185268. Findings We conducted the study between Feb 21, 2018, and May 7, 2021. We assessed 1171 patients for eligibility and 691 were ineligible; therefore, we enrolled and followed up 480 participants. 240 (50%) were iron deficient and 240 (50%) were iron replete, 95 (20%) were women, 385 (80%) were men, and 453 (94%) were White. Complete data was available for 479 individuals (240 in the iron deficient group and 239 in the iron replete group) for the primary endpoint. The iron deficient group had a median of 22.87 days (IQR 20.65 to 24.06) alive and at home at postoperative day 30, and the iron replete group had a median of 23.18 days (IQR 20.69 to 24.70). The unadjusted difference in medians between the groups was -0.18 days (95% CI -0.73 to 0.36; p=0.51) and the adjusted difference in medians between the groups was -0.11 days (95% CI -0.66 to 0.45; p=0.70). Interpretation In non-anaemic adults undergoing elective cardiac surgery, our findings suggest that patients with iron deficiency do not have a reduction in days alive and at home at postoperative day 30 compared with patients who have a normal iron status. Routine preoperative investigation for iron deficiency in patients without anaemia undergoing elective cardiac surgery using the definitions we tested might be low-value care. Copyright (C) 2022 Published by Elsevier Ltd. All rights reserved.