Associations between non-anaemic iron deficiency and outcomes following elective surgery for colorectal cancer: a prospective cohort study*

*Presented in part at the 2024 Australian and New Zealand College of Anaesthetists Annual Scientific Meeting, 4 May 2024, Brisbane, Australia.

Background
Iron deficiency is present in up to 75% of patients presenting for colorectal cancer surgery. It is unclear whether iron deficiency without anaemia is associated with worse postoperative outcomes. We hypothesised that, in adults without anaemia undergoing surgery for colorectal cancer, iron deficiency would be associated with worse postoperative outcomes relative to an iron-replete state.

Methods
We performed a prospective, observational study, recruiting adults (aged ≥ 18 y) without anaemia who were undergoing surgery for colorectal cancer in 16 hospitals across Australia and Aotearoa/New Zealand. Anaemia was defined as a haemoglobin concentration < 130 g.l-1 for men and < 120 g.l-1 for women. Iron deficiency was defined primarily as transferrin saturation < 20%. The primary endpoint was days alive and at home on postoperative day 90. The primary endpoint analysis was adjusted for surgical risk based on recruiting institution; sex; Charlson comorbidity index; CR-POSSUM score; surgical approach; and requirement for neoadjuvant therapy.

Results
Of 420 patients, 170 were iron deficient and 250 were iron replete. The median (IQR [range]) days alive and at home in the iron-deficient group was 84.0 (80.7–85.9 [0–88.2]) days and in the iron-replete group was 83.1 (78.7–85.1 [0–88.9]) days. The unadjusted difference in medians between groups was 0.9 (95%CI 0–1.8, p = 0.047) days and the adjusted difference was 0.9 (95%CI 0–1.80, p = 0.042) days, favouring the iron-deficient group.

Conclusions
In adult patients without anaemia undergoing surgery for colorectal cancer, iron deficiency defined by transferrin saturation < 20% was not associated with worse patient outcomes and appeared to be associated with more days alive and at home on postoperative day 90.