Influence of Non-Anaemic Iron Deficiency on Outcomes Following Cardiac Surgery

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Adequate iron stores are essential for the ability of the body to produce new red blood cells, and the key component of those red blood cells, haemoglobin. A low blood concentration of haemoglobin is referred to as “anaemia”, and is often due to low iron stores, or an inability for the bone marrow to access them. This latter phenomenon is referred to as “iron deficiency”. Iron deficiency and anaemic may exist in a patient separately, or together. A combination of the two is termed “iron deficiency anaemia”, and patients with the condition are said to be “anaemic”. Iron deficiency anaemia has long been associated with worse outcomes for patients undergoing cardiac surgery. Compared to a normal person, the patient with iron deficiency anaemia has a higher risk of requiring a blood transfusion, sustaining a kidney injury, or dying following their operation. There is another group that, up until now, has been poorly studied: those patients who are iron deficient, but not anaemic. Whilst these patients may have a normal haemoglobin concentration in their blood prior to surgery, inevitable blood loss during surgery and the inflammation during and afterwards causes the haemoglobin concentration to fall. If the patient has inadequate stores of iron, or is unable to access those stores, these patients will be unable to increase their production of haemoglobin. Hypothetically, these patients are at risk of many of the complications that patients with anaemia prior to their operation will face. However, because this research question is yet to be formally studied, it is not known whether or not this is correct. Proposed trial and investigators The IDOCS study has been designed to test this theory. Patients with iron deficiency, but who are not anaemic before their operation will be followed during and after their surgery and compared to a cohort of normal patients (who are iron replete and not anaemic) as a reference point. If the trial hypothesis is correct, patients who are iron deficient but not anaemic will have worse outcomes than those patients who are not anaemic and iron replete. IDOCS will be undertaken at two major tertiary hospitals in Melbourne: The Alfred and the Austin Hospital. Significance If the hypothesis of IDOCS is proven, it will identify a new group of patients who are at risk of poor outcomes following cardiac surgery, opens an exciting new frontier in preparing patients for these procedures, and improving survival and reducing complications from the operation.