Sample size calculation

Available data in the literature regarding the differences in the investigated endpoints and elderly patients are scarce. Therefore, we performed a sample size calculation using data from the Hungarian Gastrointestinal Bleeding Registry collected between 2020 December and 2022. August.³¹ Post-hoc analysis of all patients who fit our current inclusion criteria and received oral iron at discharge (20 patients) resulted in a 20% occurrence for our primary outcome within 3 months. Reasons for mortality (20/3) and readmission (20/1) were related to ischaemic events. The assessed effect size is similar to already published data. A cohort analysis with elderly patients (>65 years) showed a 4.5% mortality rate for the whole population and a 32% 30-day readmission rate with anaemia. Considering that 28% of that cohort had malignancy and authors assessed all causes of readmission, a 15%–20% lower rate for unplanned rehospitalisation due to anaemia could be imagined if the iron stores are not replenished fast enough.³² Also, another study showed that when elderly patients are discharged with moderate or severe microcytic anaemia, the 3-month mortality rate can reach 8% (without excluding patients with cancer—22% of the cases).³³

Based on the RCT of Bager et al, participants receiving intravenous iron had normalised Hb levels after 1 month. Data are lacking about the effect of intravenous iron on the investigated outcomes. However, results from other study populations found a 5% rate of anaemia-related events leading to hospitalisation only with intravenous iron^{34 35} and 0% mortality (two studies with small sample sizes).^{8 10} Due to unlimited data, we assumed that intravenous iron could result in at least a 50% risk decrease (to 10%) after non-variceal GIB since it could result in a quicker heamatopoiesis, preventing ischaemic events.¹⁰

With a 30% dropout rate,¹⁰ using a power of 80% and a significance level of 5% (two-sided χ² test) to measure the treatment effect, we calculated a sample size of 570.