Abstract Background and Aims In vivo iron levels can be adjusted through intestinal iron absorption to be maintained at a suitable level; however, optimal iron levels in hemodialysis (HD) patients are unclear. Although serum ferritin is useful as an indicator of iron stores, it does not necessarily reflect body iron levels in HD patients with unstable hematopoiesis since iron metabolism is a semi-closed system in vivo. In this study, we investigated total body iron (TBI), new index calculated as the sum of red blood cell (RBC) iron and iron stores, during courses of low-dose oral iron replacement therapy, and evaluated in vivo iron sufficiency and its indicators in HD patients. Method We analyzed data on 105 courses of low-dose iron replacement therapy (50–120 mg of iron daily) administered to 83 patients with serum ferritin <60 ng/mL and Hb <12 g/dL undergoing maintenance hemodialysis at our institution. Low-dose oral iron replacement therapy was initiated between August 2016 and June 2023 and continued for at least seven months. All blood samples were collected at the start of hemodialysis at the beginning of the week. Blood examinations were performed twice a month, and patients were given darbepoetin alfa (DA), long-acting ESAs to maintain Hb at the target level of 10–12 g/dL, in accordance with the guidelines of the Japanese Society for Dialysis Therapy. Iron-related parameters were determined based on blood samples collected once a month, with TSAT calculated from serum iron (Fe) and total iron-binding capacity (TIBC), using the following equation. TSAT=Fe/TIBC × 100. We evaluated changes in TBI, RBC iron, and iron stores from the initiation of treatment to month 7, in two groups of patients, namely, iron-therapy responders and non-responders. Furthermore, we investigated factors associated with steady-state TBI. TBI was regarded as achieving a steady state during the course of therapy when the trend shifted from an increase and the difference from the value at one month was less than or equal to zero. TBI was calculated using the formula proposed by Cable et al (Transfusion. 2016, 56, 2005). Results Mean age was 68.1±12.6 years and median time on hemodialysis was 6.6 years. Of the 105 courses of therapy, 75 were delivered to men and 30 to women, and 66.7% of the patients had diabetic nephropathy. The patients had a mean Hb level of 10.4±0.7 g/dL, a mean serum ferritin level of 27.3±12.5 ng/mL, mean transferrin saturation (TSAT) of 18.1%±5.9%, and a median C-reactive protein level of 0.1 mg/dL at the start of each course. TBI showed significant increases until month 4 and plateaued thereafter in iron-therapy responders, and tended to increase and then reached a similar plateau in non-responders (month 7: 1900±447 vs. 1900±408 mg, Fig. 1). As for RBC iron, iron-therapy responders showed significant monthly increases up to month 3, whereas non-responders showed constant values. Regarding iron stores, iron-therapy responders showed significant monthly increases up to month 5, while non-responders showed a significant increase only at month 1. DA per body weight showed a significant decrease at month 3 and 4 in the effective group, but a slight increase in the non-responder group. Steady-state TBI did not correlate with Hb or serum ferritin, but was strongly correlated with body surface area (BSA) using the Du Bois formula [TBI=−791.914 + 1628.606 × BSA (m2); R2=0.88, p<0.001, Fig. 2]. Conclusion This study showed that hemodialysis patients can increase their body iron levels during oral iron replacement therapy and maintain them at the same level after sufficiency has been achieved, suggesting activation of a “mucosal block.” Furthermore, this result also suggests that determining iron sufficiency based on serum ferritin alone is difficult in HD patients with fluctuations in Hb. However, regression equations using steady-state TBI and BSA showed a high degree of fit. Therefore, BSA might potentially be used in estimations of TBI sufficiency, which may be useful for avoiding excessive iron dosage.
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Oct 1, 2024
Nanako Oshiro + 3
Open Access