Predictors of the response to treatment in anemic hemodialysis patients with high serum ferritin and low transferrin saturation

Early erythroferrone levels can predict the long-term haemoglobin responses to erythropoiesis-stimulating agents

BACKGROUND AND PURPOSE

Our previous study reported that erythroferrone (ERFE), a newly identified hormone produced by erythroblasts, responded to recombinant human erythropoietin (rHuEPO) sensitively but its dynamics was complicated by double peaks and circadian rhythm. This study intends to elucidate the underlying mechanisms for the double peaks of ERFE dynamics and further determine whether early ERFE measurements can predict haemoglobin responses to rHuEPO.

EXPERIMENTAL APPROACH

By using the purified recombinant rat ERFE protein and investigating its deposition in rats, the production of ERFE was deconvoluted. To explore the role of iron in ERFE production, we monitored short-term changes of iron status after injection of rHuEPO or deferiprone. Pharmacokinetic/pharmacodynamic (PK/PD) modelling was used to confirm the mechanisms and examine the predictive ability of ERFE for long-term haemoglobin responses.

KEY RESULTS

The rRatERFE protein was successfully purified. The production of ERFE was deconvoluted and showed two independent peaks (2 and 8 h). Transient iron decrease was observed at 4 h after rHuEPO injection and deferiprone induced significant increases of ERFE. Based on this mechanism, the PK/PD model could characterize the complex dynamics of ERFE. In addition, the model predictions further revealed a stronger correlation between ERFE and haemoglobin peak values than that for observed values.

CONCLUSIONS AND IMPLICATIONS

The complex dynamics of ERFE should be composited by an immediate release and transient iron deficiency-mediated secondary production of ERFE. The early peak values of ERFE, which occur within a few hours, can predict haemoglobin responses several weeks after ESA treatment.

[Evaluation of serum iron as a predictor of a hemoglobin response to injectable iron treatment in chronic hemodialysis patients]

BACKGROUND

The detection and correction of iron deficiency are essential for the treatment of anemia in chronic hemodialysis patients. The aim of our study was to assess the ability of serum iron to predict hemoglobin response to intravenous iron supplementation in hemodialysis patients.

METHODS

It is a retrospective study in 91 hemodialysis patients during 2016 at Clermont-Ferrand University Hospital for whom intravenous iron supplementation had been started. A responder patient was defined as an increase in hemoglobin greater than or equal to 1 g/dL/month and/or a decrease in the dose of erythropoiesis stimulating agent after two months of iron supplementation.

RESULTS

In responding patients, serum iron was significantly lower (6.7 ± 2.7 μmol/L) compared to non-responding patients (8.9±2.9 μmol/L; P<0.001). The positive response to iron supplementation was significantly associated with low serum iron (odds ratio = 0.58 [0.42-0.81]; P=0.002) in a logistic regression model taking into account ferritin, transferrin saturation coefficient, dose variation monthly iron and erythropoiesis stimulating agent and the duration of dialysis. The area under the receiver operating characteristic curve of serum iron, ferritin and transferrin saturation coefficient to predict the response to iron supplementation were 0.72, 0.51 and 0.64, respectively (serum iron versus ferritin [P=0.006] and serum iron versus transferrin saturation coefficient [P=0.04]). The sensitivity for serum iron below 7.5 μmol/L was better than that for ferritin below 86 ng/mL (P<0.001) and the specificity for serum iron below 7.5 μmol/L was better than that for TSC less than 19% (P=0.02).

CONCLUSION

Serum iron below 7.5 μmol/L can predict the success of the response to iron supplementation in chronic hemodialysis patients.

Real-World Performance of High-Flux Dialyzers in Patients With Hypoalbuminemia

There is little research on factors that influence the choice of dialyzer in patients undergoing hemodialysis. In patients at risk for poorer outcomes, including those with hypoalbuminemia, understanding how this choice impacts clinical parameters could inform patient management. The objective of this real-world analysis was to evaluate the use and performance of four single-use (i.e., nonreuse [NR]), high-flux Optiflux dialyzers with varying surface areas (F160NR [1.5 m2], F180NR [1.7 m2], F200NR [1.9 m2], and F250NR [2.5 m2]) in patients (N = 271) with baseline hypoalbuminemia (≤3.5 g/dl) receiving hemodialysis at a medium-sized dialysis organization. Thrice weekly, in-center dialysis was delivered for 6 months without adjustments to the hemodialysis prescription. Larger dialyzers were more frequently used in men, patients with higher body mass indices, and those with diabetes. Increases in serum albumin from baseline (month 1) to month 6 (p < 0.05) were observed with all dialyzer sizes. A mean increase in hemoglobin of 0.31 g/dl was also observed (p < 0.001). Among patients exhibiting increased serum albumin levels (n = 177), reductions in the neutrophil-to-lymphocyte ratio, a marker of inflammation, were observed (mean: 0.90; p < 0.001). These results support the use of high-flux dialyzers in patients with hypoalbuminemia.

Hyporesponsiveness to long-acting erythropoiesis-stimulating agent is related to the risk of cardiovascular disease and death in Japanese patients on chronic hemodialysis: observational cohort study

Background

Responsiveness to erythropoiesis-stimulating agents (ESAs) is thought to be related to prognosis in patients on hemodialysis. A multi-center, prospective cohort study was conducted to investigate the effects of hyporesponsiveness to long-acting ESAs on cardiovascular events and mortality in Japanese patients on chronic hemodialysis.

Methods

A total of 127 chronic hemodialysis patients treated with long-acting ESAs were followed-up prospectively. Responsiveness to ESA was evaluated using an erythropoietin resistance index (ERI) calculated by dividing the weekly body-weight-adjusted ESA dose by the hemoglobin concentration. The primary endpoint of this survey was defined as a combination of cardiovascular events and all-cause deaths. The association between hyporesponsiveness to ESAs evaluated by the highest quartile of the ERI and the primary endpoint was investigated.

Results

During the follow-up period (median 4.6 years), 32 patients reached the primary end point. Kaplan-Meier curve analysis showed that patients with ESA hyporesponsiveness belonging to the highest quartile of the ERI reached the primary end point more frequently than those without (P = 0.031). Cox regression analysis showed that an ERI in the highest quartile was an independent predictor of the primary end point, even after adjustment using a propensity score (hazard ratio 2.76, 95% confidence interval 1.19–6.40).

Conclusions

ESA hyporesponsiveness in hemodialysis patients treated with long-acting ESAs is related to cardiovascular events and death.

Biomarkers of iron metabolism in chronic kidney disease

Iron is the most abundant transition metal in the human body and an essential element required for growth and survival. Our understanding of the molecular control of iron metabolism has increased dramatically over the past 20 years due to the discovery of hepcidin, which regulates the uptake of dietary iron and its mobilization from macrophages and hepatic stores. Anemia and iron deficiency are common in chronic kidney disease. The pathogenesis of anemia of chronic kidney disease is multifactorial. Correction of anemia requires two main treatment strategies: increased stimulation of erythropoiesis, and maintenance of an adequate iron supply to the bone marrow. However, there are still many uncertainties in regard to iron metabolism in patients with chronic kidney disease and in renal replacement therapy. The aim of this review was to summarize the current knowledge on iron metabolism in this population, including new biomarkers of iron status. There is an area of uncertainty regarding diagnostic utility of both erythroferrone (ERFE) and hepcidin in end-stage renal disease (ESRD) patients. Higher concentration of hepcidin in oligoanuric patients may reflect decreased renal clearance. Furthermore, the hepcidin-lowering effect of ERFE in ESRD patients treated with erythropoiesis-stimulating agents (ESAs) may be blunted by underlying inflammation and concomitant iron treatment. Thus, future studies should validate the use of ERFE as a biomarker of erythropoiesis and predictor of response to iron and ESA therapy in dialysis-dependent patients.

Diagnosis of iron deficiency in hemodialysis patients: Usefulness of measuring reticulocyte hemoglobin equivalent

The evaluation of iron status in dialysis patients provides information essential to the planning of adequate recombinant human erythropoietin treatment. To diagnose iron deficiency in patients undergoing hemodialysis (HD), reticulocyte hemoglobin content and percentage of hypochromic red cells are incorporated into the European best practice guidelines on anemia management in chronic kidney disease (CKD), the mean reticulocyte hemoglobin content (Ret-HE) was proposed as alternatives to standard biochemical tests. Reticulocyte hemoglobin content and percentage of hypochromic red cells are incorporated into the European best practice guidelines on anemia management in CKD. Our aim was to assess the value of Ret-HE parameter, in terms of the sensitivity and specificity for detecting iron deficiency, in HD patients. We studied 50 patients undergoing HD three times weekly , to clarify the accuracy of Ret-HE in diagnosing iron deficiency in dialysis patients, we initially compared Ret-HE with such iron parameters as serum ferritin levels, transferrin saturation, and hypochromic red blood cell (Hypo%) which has been established as indicators of functional iron deficiency. Ret-HE mean value in anemic patients was (25.84 ± 4.23 pg) and had good correlation (P <0.001) between Ret-HE, serum iron, ferritin, transferrin, and transferin saturation in dialysis patients. Receiver operating characteristic curve analysis revealed, values of the area was 0.887, and at a cutoff value of 27.0 pg, a sensitivity of 90.4% and a specificity of 80.8% were achieved. The newly proposed Ret-HE can provide clinicians with information equivalent to iron deficiency anemia markers. Ret-HE is a new parameter that is easily measurable is suggested as reliable parameters for the study of erythropoiesis status in HD patients.

Molecular perspective of iron uptake, related diseases, and treatments

Iron deficiency anemia and anemia of chronic disorders are the most common types of anemia. Disorders of iron metabolism lead to different clinical scenarios such as iron deficiency anemia, iron overload, iron overload with cataract and neurocognitive disorders. Regulation of iron in the body is a complex process and different regulatory proteins are involved in iron absorption and release from macrophages into hematopoietic tissues. Mutation in these regulatory genes is the most important cause of iron refractory iron deficiency anemia (IRIDA). This review provides a glance into the iron regulation process, diseases related to iron metabolism, and appropriate treatments at the molecular level.

Association between serum ferritin and mortality: findings from the USA, Japan and European Dialysis Outcomes and Practice Patterns Study

Background

The Kidney Disease: Improving Global Outcomes guidelines have cautioned against administering intravenous (IV) iron to hemodialysis patients with high serum ferritin levels due to safety concerns, but prior research has shown that the association between high ferritin and mortality could be attributed to confounding by malnutrition and inflammation. Our goal was to better understand the ferritin-mortality association and relative influence of IV iron and inflammation in the USA, where ferritin levels have recently increased dramatically, and in Europe and Japan, where ferritin levels are lower and anemia management practices differ.

Methods

Data from 18 261 patients in Phases 4 and 5 (2009-15) of the international Dialysis Outcomes and Practice Patterns Study, a prospective cohort study, were analyzed. Using Cox regression, we modeled the association between baseline ferritin and 1-year mortality with restricted cubic splines and assessed the impact of potential confounders.

Results

Median ferritin levels were 718 ng/mL in the USA, 405 in Europe and 83 in Japan. High ferritin levels were associated with elevated mortality (relative to region-specific medians) in all three regions. The strength of this association was attenuated more by adjustment for malnutrition and inflammation than by IV iron and erythropoiesis-stimulating agent dose in each region.

Conclusion

The utility of high ferritin as a biomarker for clinical risk due to excess iron stores may be limited, although caution regarding IV iron dosing to higher upper ferritin targets remains warranted. Research to resolve biomarker criteria for iron dosing, and whether optimal anemia management strategies differ internationally, is still needed.

Relationships between iron dose, hospitalizations and mortality in incident haemodialysis patients: a propensity-score matched approach

Background

Intravenous iron management is common in the haemodialysis population. However, the safest dosing strategy remains uncertain, in terms of the risk of hospitalization and mortality. We aimed to determine the effects of cumulative monthly iron doses on mortality and hospitalization.

Methods

This multicentre observational retrospective propensity-matched score study included 1679 incident haemodialysis patients. We measured baseline demographic variables, haemodialysis clinical parameters and laboratory analytical values. We compared outcomes among quartiles of cumulative iron dose (mg/kg/month). We implemented propensity-score matching (PSM) to reduce confounding due to indication. In the PSM cohort (330 patients), we compared outcomes between groups that received cumulative iron doses above and below 5.66 mg/kg/month.

Results

Kaplan-Meier analyses showed that the high iron dose group had significantly worse survival than the low iron dose group. A univariate analysis indicated that the monthly iron dose could significantly predict mortality. However, a multivariate regression did not confirm that finding. The multivariate regression analysis revealed that iron doses  >5.58 mg/kg/month were not associated with elevated mortality risk, but they were associated with elevated risks of all-cause and cardiovascular-related hospitalizations. These results were ratified in the PSM population.

Conclusions

Intravenous iron administration is advisable for maintaining haemoglobin levels in patients that receive haemodialysis. Our data suggested that large monthly iron doses, adjusted for body weight, were associated with more hospitalizations, but not with mortality or infection-related hospitalizations.

Impact of Inflammation on Ferritin, Hepcidin and the Management of Iron Deficiency Anemia in Chronic Kidney Disease

Iron deficiency anemia (IDA) is a major problem in chronic kidney disease (CKD), causing increased mortality. Ferritin stores iron, representing iron status. Hepcidin binds to ferroportin, thereby inhibiting iron absorption/efflux. Inflammation in CKD increases ferritin and hepcidin independent of iron status, which reduce iron availability. While intravenous iron therapy (IIT) is superior to oral iron therapy (OIT) in CKD patients with inflammation, OIT is as effective as IIT in those without. Inflammation reduces predictive values of ferritin and hepcidin for iron status and responsiveness to iron therapy. Upper limit of ferritin to predict iron overload is higher in CKD patients with inflammation than in those without. However, magnetic resonance imaging studies show lower cutoff levels of serum ferritin to predict iron overload in dialysis patients with apparent inflammation than upper limit of ferritin proposed by international guidelines. Compared to CKD patients with inflammation, optimal ferritin levels for IDA are lower in those without, requiring reduced iron dose and leading to decreased mortality. The management of IDA should differ between CKD patients with and without inflammation and include minimization of inflammation. Further studies are needed to determine the impact of inflammation on ferritin, hepcidin and therapeutic strategy for IDA in CKD.

Influence of Intravenous Iron Therapy on Novel Markers of Iron Deficiency

Background

Detection of iron deficiency in patients with end-stage renal disease (ESRD) remains challenging due to the lack of reliable markers. The immature reticulocyte fractions (IRF) RET-Y and RBC-Y may serve as useful novel markers. We investigated the ability of IRF to detect functional iron deficiency in ESRD patients in comparison to Serum ferritin (SF) and Transferrin saturation (TSAT) and the influence of intravenous iron therapy on these markers.

Methods

Cross sectional (n=40) and prospective (n=20) studies of hemodialysis patients were performed; 20 patients received intravenous iron (200 mg) monthly and were followed up for 5 months. Iron deficiency was defined as SF ≤200μg/L and/or TSAT ≤20%. A RBC-Y ≤171 and/or RET-Y ≤168.7 were criteria for iron deficiency. Correlations between traditional and novel markers were examined. Results are given as mean±SEM. Paired t-test was used to test for significance.

Results

27 male and 13 female patients, mean age of 56.7±3.02 years were enrolled in the crosssectional study. TSAT correlated with RBC-Y and RET-Y, r=0.47 and 0.61, respectively. Correlations for SF with RBC-Y and RET-Y were r=0.23 and 0.22, respectively. In the prospective component (11 males and 9 females of mean age 60±3.4 years), RET-Y and RBC -Y remained stable during iron therapy. The coefficients of variation were RBC-Y 2.54%, RET-Y 4.23%, TSAT 28.74% and SF 35.34%.

Conclusions

RBC-Y and RET-Y correlated with TSAT and SF allowing detection of functional iron deficiency. These measures were less susceptible to fluctuations than traditional markers.

Diagnosis of Iron-Deficiency Anemia in Chronic Kidney Disease

Anemia is a common and clinically important consequence of chronic kidney disease (CKD). It is most commonly a result of decreased erythropoietin production by the kidneys and/or iron deficiency. Deciding on the appropriate treatment for anemia associated with CKD with iron replacement and erythropoietic-stimulating agents requires an ability to accurately diagnose iron-deficiency anemia. However, the diagnosis of iron-deficiency anemia in CKD patients is complicated by the relatively poor predictive ability of easily obtained routine serum iron indices (eg, ferritin and transferrin saturation) and more invasive gold standard measures of iron deficiency (eg, bone marrow iron stores) or erythropoietic response to supplemental iron. In this review, we discuss the diagnostic utility of currently used serum iron indices and emerging alternative markers of iron stores.

Serum Hepcidin and Iron Indices Affect Anemia Status Differently According to the Kidney Function of Non-Dialysis Chronic Kidney Disease Patients: Korean Cohort Study For Outcome in Patients with Chronic Kidney Disease (KNOW-CKD)

BACKGROUND/AIMS

No studies have examined the association among serum hepcidin, iron indices, or anemia status based on the kidney function of non-dialysis chronic kidney disease (CKD) patients.

METHODS

We reviewed data of 2238 patients from a large-scale multicenter prospective Korean study (2011-2016) and excluded 198 patients with missing data regarding serum hepcidin, hemoglobin, transferrin saturation (TSAT), ferritin, and usage of erythropoiesis-stimulating agents (ESA) or supplemental iron and 363 patients using ESA or supplemental iron. Finally, 1677 patients were included.

RESULTS

The mean patient age was 53.5 years, and 65.4% were men. TSAT and serum hepcidin were significantly associated with anemia status, whereas serum ferritin was not, regardless of anemia severity. For patients with an estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73 m2, a 10% increase of TSAT was associated with hemoglobin <13 g/dL (odds ratio [OR], 0.628; 95% confidence interval [CI], 0.515-0.765; P<0.001) and hemoglobin <11.5 g/dL (OR, 0.672; 95% CI, 0.476-0.950; P=0.024), whereas a 10-ng/mL increase of serum hepcidin was associated with hemoglobin <11.5 g/dL (OR, 1.379; 95% CI, 1.173-1.620; P<0.001) and hemoglobin <10.0 g/dL (OR, 1.360; 95% CI, 1.115-1.659; P=0.002) for patients with eGFR <45 mL/min/1.73 m2 according to multivariate logistic analysis.

CONCLUSIONS

TSAT was associated with less severe anemia in early CKD patients. Serum hepcidin was associated with more severe anemia in advanced CKD patients.

Diagnosing and preventing iron overload

Absolute or functional iron (Fe) deficiency is an important determinant of anemia in hemodialysis patients and parenteral Fe is routinely used to treat this condition in conjunction with erythropoiesis stimulating agents. While restoration of hemoglobin toward the target range is a good outcome of Fe replacement, it is well known that Fe overload and toxicity may be adverse consequences of this therapy. Dialysis clinical practice guidelines recommend tailoring Fe therapy based on transferrin saturation and serum ferritin levels. Unfortunately, serum Fe markers may not accurately reflect the amount of Fe in the body, because factors such as infections, inflammation, or malignancy can alter serum ferritin levels. Some recent trials in dialysis patients receiving high intravenous Fe doses have shown increased cardiovascular morbidity and mortality and studies using magnetic resonance imaging (MRI) in this population have shown excessive tissue liver iron content (LIC) suggesting Fe overload. While LIC measured by MRI correlates well with LIC quantitated by liver biopsy, it only represents a surrogate marker for total body Fe and its clinical relevance in dialysis patients in terms of mortality and morbidity remains to be demonstrated. Nevertheless, these recent findings challenge the use of current serum Fe markers recommended by clinical guidelines to guide safe Fe therapy in dialysis patients. While not yet established for the routine screening of dialysis patients for Fe overload, MRI should be considered in patients who have received a high cumulative dose of intravenous Fe, or have long cumulative dialysis vintage. Further studies are needed to assess how MRI will alter management.

Plasma vitamin C levels in ESRD patients and occurrence of hypochromic erythrocytes

INTRODUCTION

The achievement of erythropoiesis in hemodialysis (HD) patients is typically managed with erythropoiesis-stimulating-agents (ESA's) and intravenous iron (IV-iron). Using this treatment strategy, HD patients frequently show an elevated fraction of red blood cells (RBC) with hemoglobin (Hb) content per cell that is below the normal range, called hypochromic RBC. The low Hb content per RBC is the result of the clinical challenge of providing sufficient iron content to the bone marrow during erythropoiesis. Vitamin C supplements have been used to increase Hb levels in HD patients with refractory anemia, which supports the hypothesis that vitamin C mobilizes iron needed for Hb synthesis.

METHODS

We conducted a cross-sectional survey in 149 prevalent HD patients of the percent hypochromic RBC, defined as RBC with Hb < 300 ng/uL of packed RBC, in relation to plasma vitamin C levels. We also measured high-sensitivity CRP, (hs-CRP), iron, and ferritin levels. and calculated ESA dose.

FINDINGS

High plasma levels of vitamin C were negatively associated with hypochromic RBC (P < 0.003), and high ESA doses were positively associated (P < 0.001). There was no significant association of hs-CRP with percent hypochromic RBC.

DISCUSSION

This finding supports the hypothesis that vitamin C mobilizes iron stores, improves iron delivery to the bone marrow, and increase the fraction of RBC with normal Hb content. Further research is warranted on development of protocols for safe and effective use of supplemental vitamin C for management of renal anemia.

The Growth Attainment, Hematological, Iron Status and Inflammatory Profile of Guatemalan Juvenile End-Stage Renal Disease Patients

Background

Stunting, anemia and inflammation are frequently observed in children with end-stage renal disease (ESRD).

Objectives

To assess anthropometric, hematological and inflammatory data and to study their potential interrelationship in Guatemalan juveniles undergoing hemodialysis (HD) and peritoneal dialysis (PD).

Methods

54 juveniles 7–20 years of age were recruited in FUNDANIER, Guatemala City: 27 on HD and 27 PD. Hemoglobin, serum iron, transferrin, serum transferrin receptor (sTfR), serum ferritin, transferrin saturation and iron-binding capacity, white blood cell count (WBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), as well as IL-6, IL-1 and TNF-α, weight and height were determined by standard methods. Hepcidin–25 (Hep-25) was assessed by weak cation exchange time-of-flight mass-spectrometry.

Results

92% and 55% of HD and PD children, respectively, were stunted and 95% and 85% were anemic. Among iron status biomarkers, serum ferritin was massively increased and significantly higher in the HD group compared to the PD group. Hep-25 was also greatly elevated in both groups. 41% of HD patients showed increments in three or more inflammatory biomarkers, while it was 2 or less in all PD subjects.

Conclusions

The degree of stunting, the prevalence and severity of anemia in Guatemalan juvenile ESRD far exceed the national statistics for this low-income Central American country. Ferritin and Hep-25 concentrations were elevated, with the latter to an extraordinary magnitude. Additional biomarkers of inflammation not directly related to iron status were elevated as well. The role of both disease- and environment-related factors in combination best explains the magnitude of the biomarker abnormalities.

Minor Elevation in C-Reactive Protein Levels Predicts Incidence of Erythropoiesis-Stimulating Agent Hyporesponsiveness among Hemodialysis Patients

BACKGROUND

Hemodialysis (HD) patients occasionally experience minor asymptomatic elevation in C-reactive protein (CRP) levels, which may be associated with difficulty in managing renal anemia using erythropoiesis-stimulating agents (ESAs). Here, we assessed whether elevation of CRP predicts future incidences of ESA hyporesponsiveness.

METHODS

A total of 2,956 HD patients lacking ESA hyporesponsiveness and infectious diseases were enrolled, and the association between CRP levels and incidence of ESA hyporesponsiveness was assessed. CRP levels were divided into 4 categories (normal [<1.0 mg/l], mild [1.0 ≤ CRP <3.0 mg/l], moderate [3.0 ≤ CRP <10.0 mg/l] and high [≥ 10.0 mg/l]). The primary outcome was the cumulative incidence of ESA hyporesponsiveness, defined as a failure to achieve hemoglobin level ≥ 10 g/dl despite receiving high doses of ESAs (≥ 9,000 U/week recombinant human epoetin [rHuEPO]-α or rHuEPO-β and ≥ 60 μg/week darbepoetin-α) during 12 months of follow-up.

RESULTS

The cumulative incidence of ESA hyporesponsiveness was 134 (4.8%) occurrences over 4 months and 300 (12.4%) over 12 months. The elevated CRP groups had significantly higher incidence of ESA hyporesponsiveness over 4 months of follow-up than the normal reference group (adjusted relative risk [RR] 1.6, 95% CI 1.0-2.6 for moderate; adjusted RR 2.5, 95% CI 1.5-4.1 for high). Furthermore, the association remained consistent even over 12 months (adjusted RR 1.4, 95% CI 1.0-1.8 for moderate; adjusted RR 1.6, 95% CI 1.1-2.4 for high).

CONCLUSIONS

Elevated CRP levels were associated with future incidence of ESA hyporesponsiveness from low-grade inflammation (3.0 ≤ CRP <10.0 mg/l).

Hepcidin-25, mean corpuscular volume, and ferritin as predictors of response to oral iron supplementation in hemodialysis patients

The benefit of oral iron therapy (OIT) and factors predictive of OIT response are not established in hemodialysis (HD) patients with iron deficiency anemia (IDA). We examined the values of hepcidin-25, mean corpuscular volume (MCV), and ferritin as predictors of OIT response. Oral ferrous fumarate (50 mg/day, 8 weeks) was given to 51 HD patients with IDA (hemoglobin (Hb) < 12 g/dL, ferritin < 100 ng/mL) treated with an erythropoietin activator. Sixteen patients were responders (improvement of Hb (ΔHb) ≥ 2 g/dL) and 35 were non-responders (ΔHb < 2g/dL). Baseline Hb, MCV, serum hepcidin-25, ferritin, iron parameters, and C-reactive protein (CRP) before and ΔHb after OIT were compared between groups. Hepcidin-25, MCV, ferritin, and transferrin saturation were lower in the responders than in the non-responders. Hepcidin-25 positively correlated with ferritin. Hepcidin-25, MCV, and ferritin positively correlated with baseline Hb and negatively correlated with ΔHb. Despite normal CRP levels in all patients, CRP correlated positively with hepcidin-25 and ferritin. Stepwise multiple linear regression analysis and receiver operating characteristics curve analysis revealed that hepcidin-25, MCV, and ferritin could predict OIT response. We conclude that hepcidin-25, MCV, and ferritin could be useful markers of iron storage status and may help predict OIT response in HD patients.

Iron dosing in kidney disease: inconsistency of evidence and clinical practice

The management of anemia in patients with chronic kidney disease (CKD) is difficult. The availability of erythropoiesis-stimulating agents (ESAs) has increased treatment options for previously transfusion-requiring patients, but the recent evidence of ESA side effects has prompted the search for complementary or alternative approaches. Next to ESA, parenteral iron supplementation is the second main form of anemia treatment. However, as of now, no systematic approach has been proposed to balance the concurrent administration of both agents according to individual patient's needs. Furthermore, the potential risks of excessive iron dosing remain a topic of controversy. How, when and whether to monitor CKD patients for potential iron overload remain to be elucidated. This review addresses the question of risk and benefit of iron administration in CKD, highlights the evidence supporting current practice, provides an overview of standard and potential new markers of iron status and outlines a new pharmacometric approach to physiologically compatible individualized dosing of ESA and iron in CKD patients.

The iron cycle in chronic kidney disease (CKD): from genetics and experimental models to CKD patients

Iron is essential for most living organisms but iron excess can be toxic. Cellular and systemic iron balance is therefore tightly controlled. Iron homeostasis is dysregulated in chronic kidney disease (CKD) and contributes to the anemia that is prevalent in this patient population. Iron supplementation is one cornerstone of anemia management in CKD patients, but has not been rigorously studied in large prospective randomized controlled trials. This review highlights important advances from genetic studies and animal models that have provided key insights into the molecular mechanisms governing iron homeostasis and its disturbance in CKD, and summarizes how these findings may yield advances in the care of this patient population.

Comparative study of intravenous iron versus intravenous ascorbic Acid for treatment of functional iron deficiency in patients under hemodialysis: a randomized clinical trial

Background

Functional iron deficiency (FID) may cause erythropoietin resistance in patients under hemodialysis (HD). Since the role of chronic inflammation or oxidative stress in its pathogenesis is unclear, controversy remains to whether intravenous iron or intravenous ascorbic acid (an antioxidant) can improve this anemia due to decreased iron availability.

Objectives

The current study compared the effect of intravenous iron versus intravenous ascorbic acid in the management of FID in HD patients.

Patients and Methods

Forty HD patients with hemoglobin (Hb) ≤ 11 g/dL, serum ferritin ≥ 500 ng/mL and transferrin saturation (TSAT) ≤ 25% were randomly divided into two groups. 20 patients received 100 mg of intravenous (IV) iron (group I), and 20 patients received 300 mg of IV ascorbic acid (group II) postdialysis, twice a week for 5 consecutive weeks. Hb and iron metabolism indices were measured before the onset of the study and after 12 weeks following therapy.

Results

Twenty one percent of all HD patients, exhibited high serum ferritin, low TSAT and sufficient data for analysis. Both Group I (n = 20) and Group II (n = 20) patients showed a significant increase in Hb, serum iron, and TSAT (P < 0.001). There were no significant differences between both groups in increasing Hb (P = 0.076), serum iron (P = 0.589), serum ferritin (0.725), and TSAT (P = 0.887).

Conclusions

This study showed that both IV iron and IV ascorbic acid can improve FID in HD patients. A larger randomized trial is warranted to determine the optimal management of FID in HD patients.

Intravenous Iron Repletion Does Not Significantly Decrease Platelet Counts in CKD Patients with Iron Deficiency Anemia

Purpose. We sought to investigate the effect of IV iron repletion on platelet (PLT) counts in CKD patients with iron deficiency anemia (IDA). Methods. We conducted a retrospective chart review, including all patients with CKD and IDA who were treated with iron dextran total dose infusion (TDI) between 2002 and 2007. Patient demographics were noted, and laboratory values for creatinine, hemoglobin (Hgb), iron stores and PLT were recorded pre- and post-dose. Results. 153 patients received a total of 251 doses of TDI (mean ± SD = 971 ± 175 mg); age 69 ± 12 years and Creatinine 3.3 ± 1.9 mg/dL. All CKD stages were represented (stage 4 commonest). Hgb and Fe stores improved post-TDI (P ≪ 0.001). There was a very mild decrease in PLT (pre-TDI 255 versus post-TDI 244, P = 0.30). The mild reduction in PLT after TDI remained non-significant (P > 0.05) when data was stratified by molecular weight (MW) of iron dextran used (low versus high), as well as by dose administered (<1000 versus ≥1000 mg). Linear regression analysis between pre-dose PLT and Tsat and Fe showed R2 of 0.01 and 0.04, respectively. Conclusion. Correction of iron deficiency did not significantly lower PLT in CKD patients, regardless of MW or dose used. Correlation of PLT to severity of iron deficiency was very weak.

Anaemia management protocols in the care of haemodialysis patients: examining patient outcomes

AIMS AND OBJECTIVES

To determine whether the use of a nurse-driven protocol in the haemodialysis setting is as safe and effective as traditional physician-driven approaches to anaemia management.

BACKGROUND

The role of haemodialysis nurses in renal anaemia management has evolved through the implementation of nurse-driven protocols, addressing the trend of exceeding haemoglobin targets and rising costs of erythropoietin-stimulating agents.

DESIGN

Retrospective, non-equivalent case control group design.

METHODS

The sample was from three haemodialysis units in a control group (n = 64) and three haemodialysis units in a protocol group (n = 43). The protocol group used a nurse-driven renal anaemia management protocol, while the control group used a traditional physician-driven approach to renal anaemia management. All retrospective data were obtained from a provincial renal database. Data were analysed using chi-square tests and t-tests. Patient outcomes examined were haemoglobin levels, transferrin saturation levels, erythropoietin-stimulating agents use and intravenous iron use. Cost comparisons were determined using average use of erythropoietin-stimulating agents and intravenous iron.

RESULTS

Control and protocol groups reached haemoglobin target levels. In the protocol group, 75% reached transferrin saturation target levels in comparison with 25% of the control group. Use and costs for iron was higher in the control group, while use and costs for erythropoietin was higher in the protocol group. The higher usage of erythropoietin-stimulating agents was potentially related to comorbid conditions amongst the protocol group.

CONCLUSIONS

A nurse-driven protocol approach to renal anaemia management was as effective as the physician-driven approach in reaching haemoglobin and transferrin saturation levels. Further examination of the use and dosing of erythropoietin-stimulating agents and intravenous iron, their impact on haemoglobin levels related to patient comorbidities and subsequent cost effectiveness of protocols is required.

RELEVANCE TO CLINICAL PRACTICE

Using a nurse-driven protocol in practice supports the independent nursing role while contributing to safe patient outcomes.

Changing patterns of anemia management in US hemodialysis patients

BACKGROUND

Erythropoiesis-stimulating agents and adjuvant intravenous iron have been the primary treatment for anemia in chronic kidney disease. Recent clinical and policy-related events have challenged this traditional paradigm, particularly in regard to erythropoiesis-stimulating agents. Less is known about the impact of these events on intravenous iron use.

METHODS

United States Renal Data System data (2002-2008) on Medicare hemodialysis patients were examined. For each patient, monthly intravenous iron dose, erythropoiesis-stimulating agent dose, and hemoglobin values were determined. Data were summarized by calendar quarter and plotted for the entire sample and by demographic, clinical, and facility-level subgroups. Marginal means for these variables also were computed to account for changes in patient characteristics over time.

RESULTS

Quarterly iron use increased from 64% in 2002 to 76% in 2008. Mean quarterly iron dose increased from 500 mg in 2002 to 650 mg in 2008. Mean monthly erythropoiesis-stimulating agent dose (per quarter) increased from 2002 to 2006 and then declined. Mean hemoglobin values followed a pattern similar to erythropoiesis-stimulating agent dose. The same patterns in iron, erythropoiesis-stimulating agent dose, and hemoglobin were generally observed across demographic, clinical, facility, and geographic subgroups, with some important differences between subgroups, specifically race and dialysis vintage.

CONCLUSIONS

Anemia management patterns have changed markedly between 2002 and 2008, with a steady increase in intravenous iron use even after declines in erythropoiesis-stimulating agent dose and hemoglobin. The clinical impacts of these changes need further evaluation.

Hepcidin-25 in chronic hemodialysis patients is related to residual kidney function and not to treatment with erythropoiesis stimulating agents

Hepcidin-25, the bioactive form of hepcidin, is a key regulator of iron homeostasis as it induces internalization and degradation of ferroportin, a cellular iron exporter on enterocytes, macrophages and hepatocytes. Hepcidin levels are increased in chronic hemodialysis (HD) patients, but as of yet, limited information on factors associated with hepcidin-25 in these patients is available. In the current cross-sectional study, potential patient-, laboratory- and treatment-related determinants of serum hepcidin-20 and -25, were assessed in a large cohort of stable, prevalent HD patients. Baseline data from 405 patients (62% male; age 63.7 ± 13.9 [mean SD]) enrolled in the CONvective TRAnsport STudy (CONTRAST; NCT00205556) were studied. Predialysis hepcidin concentrations were measured centrally with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Patient-, laboratory- and treatment related characteristics were entered in a backward multivariable linear regression model. Hepcidin-25 levels were independently and positively associated with ferritin (p<0.001), hsCRP (p<0.001) and the presence of diabetes (p = 0.02) and inversely with the estimated glomerular filtration rate (p = 0.01), absolute reticulocyte count (p = 0.02) and soluble transferrin receptor (p<0.001). Men had lower hepcidin-25 levels as compared to women (p = 0.03). Hepcidin-25 was not associated with the maintenance dose of erythropoiesis stimulating agents (ESA) or iron therapy. In conclusion, in the currently studied cohort of chronic HD patients, hepcidin-25 was a marker for iron stores and erythropoiesis and was associated with inflammation. Furthermore, hepcidin-25 levels were influenced by residual kidney function. Hepcidin-25 did not reflect ESA or iron dose in chronic stable HD patients on maintenance therapy. These results suggest that hepcidin is involved in the pathophysiological pathway of renal anemia and iron availability in these patients, but challenges its function as a clinical parameter for ESA resistance.

Serum ferritin concentration and transferrin saturation before liver transplantation predict decreased long-term recipient survival

Serum ferritin (SF) concentration is a widely available parameter used to assess iron homeostasis. It has been described as a marker to identify high-risk patients awaiting liver transplantation (LT) but is also elevated in systemic immune-mediated diseases, metabolic syndrome, and in hemodialysis where it is associated with an inferior prognosis. This study analyzed whether SF is not only a predictor of liver-related mortality prior to LT but also an independent marker of survival following LT. In a dual-center, retrospective study, a cohort of 328 consecutive first-LT patients from Hannover Medical School, Germany (2003-2008, follow-up 1260 days), and 82 consecutive LT patients from Regensburg University Hospital, Germany (2003-2007, follow-up 1355 days) as validation cohort were analyzed. In patients exhibiting SF ≥365 μg/L versus <365 μg/L prior to LT, 1-, 3-, and 5-year post-LT survival was 73.3% versus 81.1%, 64.4% versus 77.3%, and 61.1% versus 74.4%, respectively (overall survival P = 0.0097), which was confirmed in the validation cohort (overall survival of 55% versus 83.3%, P = 0.005). Multivariate analyses identified SF ≥365 μg/L combined with transferrin saturation (TFS) <55%, hepatocellular carcinoma, and the survival after LT (SALT) score as independent risk factors for death. In patients with SF concentrations ≥365 μg/L and TFS <55%, overall survival was 54% versus 74.8% in the remaining group (P = 0.003). In the validation cohort, it was 28.6% versus 72% (P = 0.017), respectively.

CONCLUSION

SF concentration ≥365 μg/L in combination with TFS <55% before LT is an independent risk factor for mortality following LT. Lower TFS combined with elevated SF concentrations indicate that acute phase mechanisms beyond iron overload may play a prognostic role. SF concentration therefore not only predicts pre-LT mortality but also death following LT.

Anemia in chronic kidney disease: new advances

Anemia resulting from iron and erythropoietin deficiencies is a common complication of advanced chronic kidney disease (CKD). This article covers major advances in our understanding of anemia in patients with CKD, including newly discovered regulatory molecules, such as hepcidin, to innovative intravenous iron therapies. The use of erythropoiesis-stimulating agents (ESA) in the treatment of anemia has undergone seismic shift in the past 3 years as a result of adverse outcomes associated with targeting higher hemoglobin levels with these agents. Potential mechanisms for adverse outcomes, such as higher mortality, are discussed. Despite the disappointing experience with ESAs, there is a tremendous interest in other novel agents to treat anemia in CKD. Lastly, while awaiting updated guidelines, the authors outline their recommendations on how to best manage patients who are anemic and have CKD.

Correction of iron deficiency in the cardiorenal syndrome

Impaired energy metabolism is a feature of Congestive Heart Failure (CHF). Iron deficiency has been shown to reduce energy production in the cell in animals and humans. Iron deficiency is common in both Chronic Kidney Disease (CKD) and in CHF. Recent studies suggest that iron deficiency is an independent risk factor for mortality in CHF. Studies of correction of the anemia with intravenous (IV) iron in both CKD and CHF have shown an improvement in the anemia and, in some cases, in the renal function as well. Some CHF studies of correction of the iron deficiency have shown an improvement in cardiac function and structure as well as in exercise capacity and quality of life. This occurred independent of whether or not they had anemia, suggesting that the iron deficiency itself may be independently contributing to the worsening of the CHF and CKD. If future long-term studies confirm the safety and efficacy of IV iron in the treatment of iron deficiency in CKD and CHF, this will become a new addition to the therapeutic armamentarium of the cardiorenal syndrome, and parameters of iron deficiency will become part of the routine measurements performed in both CKD and CHF whether or not the patient is anemic.

Anaemia and resistance to erythropoiesis-stimulating agents as prognostic factors in haemodialysis patients: results from the RISCAVID study

BACKGROUND

Resistance to erythropoiesis-stimulating agents (ESAs) is often associated with chronic inflammation. Here, we investigated how anaemia, ESA resistance and the plasma levels of biological markers of inflammation could influence all-cause and cardiovascular disease morbidity and mortality.

METHODS

Seven hundred and fifty-three haemodialysis (HD) patients (mean age 66 ± 14.2 years, mean dialytic age 70 ± 77 months and diabetes 18.8%) were enrolled and followed-up for 36 months. Demographic, clinical and laboratory data, co-morbidity conditions, administered drugs, all-cause mortality and fatal/non-fatal cardiovascular (CV) events were recorded. We measured ESA resistance index, C-reactive protein (CRP) and interleukin-6 (IL-6).

RESULTS

Six hundred and fifty-one patients (86.4%) received ESAs. Patients with haemoglobin level <11 g/dL (n = 225) showed increased risk of CV [relative risk (RR) 1.415, 95% confidence interval (CI) 1.046-1.914] and overall mortality (RR 1.897, 95% CI 1.423-2.530) versus patients with haemoglobin levels >11 g/dL. ESA resistance values categorized into quartiles (Quartile I <5.6, Quartile II 5.7-9.6, Quartile III 9.7-15.4 and Quartile IV >15.4) correlated with all-cause mortality and fatal/non-fatal CV events (RR 1.97, 95% CI 1.392-2.786; RR 1.619, 95% CI 1.123-2.332, respectively). Furthermore, albumin was significantly reduced versus reference patients and correlated with all-cause mortality and CV events; CRP levels were higher in hyporesponders (Quartile IV) (P < 0.001) and predicted all-cause mortality and CV events. IL-6 but not CRP was a strong predictor of ESA resistance.

CONCLUSIONS

ESA responsiveness can be considered a strong prognostic factor in HD patients and seems to be tightly related to protein-energy wasting and inflammation.

Hepcidin-25 is a marker of the response rather than resistance to exogenous erythropoietin in chronic kidney disease/chronic heart failure patients

AIMS

Erythropoietin (EPO) resistance, an important cause of anaemia in patients with heart and renal failure, is associated with increased mortality. The hypothesis of the present study was that exogenous EPO decreases hepcidin levels and that the decrease in hepcidin levels upon EPO treatment is related to the bone marrow response.

METHODS AND RESULTS

In the EPOCARES trial, patients with renal failure (glomerular filtration rate 20-70 mL/min), heart failure, and anaemia were randomized to receive 50 IU/kg/week EPO (n = 20) or not (n = 13). Haemoglobin (Hb), hepcidin-25, ferritin, reticulocytes, serum transferrin receptor (sTfR), IL-6, and high-sensitivity C-reactive protein were measured at baseline and during treatment. Hepcidin-25 was measured by weak cation exchange chromatography/matrix assisted laser desorption ionization time-of-flight mass spectrometry. Baseline hepcidin levels were increased compared with a healthy reference population and were inversely correlated with Hb (r(2) = 0.18, P = 0.02), and positively with ferritin (r(2) = 0.51, P < 0.001), but not with renal function, high-sensitivity C-reactive protein or IL-6. Erythropoietin treatment increased reticulocytes (P < 0.001) and sTfR (P < 0.001), and decreased hepcidin (P < 0.001). Baseline hepcidin levels and the magnitude of the decrease in hepcidin correlated with the increase in reticulocytes (r(2) = 0.23, P = 0.03) and sTfR (r(2) = 0.23, P = 0.03) and also with the Hb response after 6 months (r(2) = 0.49, P = 0.001).

CONCLUSION

In this group of patients with combined heart and renal failure and anaemia, increased hepcidin levels were associated with markers of iron load and not with markers of inflammation. The (change in) hepcidin levels predicted early and long-term bone marrow response to exogenous EPO. In our group hepcidin seems to reflect iron load and response to EPO rather than inflammation and EPO resistance.

Diagnosis of iron deficiency in patients undergoing hemodialysis

To diagnose iron deficiency in patients undergoing hemodialysis, the percentage of hypochromic RBCs (with cellular hemoglobin concentration <280 g/L [HYPO%]) and mean reticulocyte hemoglobin content (CHret) provided by the Siemens ADVIA 120 and 2120 analyzers (Siemens Diagnostic Solutions, Tarrytown, NY) were proposed as alternatives to biochemical tests. Sysmex, with its XE-5000 analyzer (Sysmex, Kobe, Japan), also proposed the percentage of erythrocytes with cellular hemoglobin content lower than 17 pg (%Hypo-He) and equivalent of the mean reticulocyte hemoglobin content (Ret-He) with similar clinical applications. Our aim was to verify the clinical usefulness of the biochemical and cellular parameters as predictors of iron deficiency in patients undergoing long-term hemodialysis. We studied 69 patients undergoing hemodialysis 3 times weekly. The baseline values of serum ferritin and percentage of transferrin saturation were poor predictors of iron responsiveness. Better ability was demonstrated by reticulocyte indices (area under the curve [AUC], 0.74 for CHret and 0.72 for Ret-He; best cutoff values, 31.2 and 30.6 pg, respectively) and erythrocyte parameters (AUC, 0.72 for HYPO% and 0.68 for %Hypo-He; best cutoff values, 5.8 and 2.7, respectively). The newly proposed Ret-He and %Hypo-He can provide clinicians with information equivalent to CHret and HYPO%.

Iron, inflammation, dialysis adequacy, nutritional status, and hyperparathyroidism modify erythropoietic response

BACKGROUND AND OBJECTIVES

The erythropoietic response in hemodialysis patients depends on several physiologic factors. Most epidemiologic studies include the effect of these factors by representing them as confounders. This study tested the hypothesis that iron stores, inflammation, dialysis adequacy, nutritional status, and hyperparathyroidism act as nonlinear effect modifiers of the erythropoietic response and quantified the magnitude of those effects over clinically relevant ranges.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The following retrospective data from 209 hemodialysis patients receiving Epoetin alfa (Epo) were collected: monthly: predialysis hemoglobin (Hgb), transferrin saturation, serum albumin, dialysis adequacy (Kt/V); quarterly: predialysis serum ferritin and intact parathyroid hormone over a period of 13 to 69 months. The study analyzed the dynamic relationship between hemoglobin and Epo, considering nonlinear effect modification by ferritin, transferrin saturation, Kt/V, albumin, and parathyroid hormone individually.

RESULTS

Maximum Hgb response to Epo was achieved for serum ferritin between 350 and 500 ng/ml, transferrin saturation greater than 30%, Kt/V greater than 1.4, and albumin greater than 3.8 g/dl. Hgb sensitivity to Epo decreases by about 30% as parathyroid hormone increases from 0 through 1000 pg/ml.

CONCLUSIONS

Serum ferritin, transferrin saturation, Kt/V, serum albumin, and intact parathyroid hormone are markers of nonlinear effect modification of the erythropoietic response in hemodialysis patients.

Hepcidin for clinicians

Despite the use of erythropoiesis-stimulating agents (ESAs), the anemia of chronic kidney disease (CKD) can be resistant to therapy. Both absolute and functional iron deficiency along with inflammation can contribute to ESA resistance and can be difficult to identify with current-day markers of iron storage. Hepcidin, a small peptide produced by the liver, is a recently discovered key regulator of iron homeostasis. Via regulation of ferroportin, hepcidin inhibits intestinal iron absorption and iron release from macrophages and hepatocytes. Because of its renal elimination and regulation by inflammation, it is possible that progressive renal insufficiency leads to altered hepcidin metabolism, subsequently affecting enteric absorption of iron and the availability of iron stores. Thus, hepcidin likely plays a major role in the anemia of CKD as well as ESA resistance. This article discusses the biologic actions and regulation of hepcidin along with reviewing studies of hepcidin in CKD.

Hepcidin--a potential novel biomarker for iron status in chronic kidney disease

BACKGROUND AND OBJECTIVES

Hepcidin is a key regulator of iron homeostasis, but its study in the setting of chronic kidney disease (CKD) has been hampered by the lack of validated serum assays.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study reports the first measurements of bioactive serum hepcidin using a novel competitive ELISA in 48 pediatric (PCKD2-4) and 32 adult (ACKD2-4) patients with stages 2 to 4 CKD along with 26 pediatric patients with stage 5 CKD (PCKD5D) on peritoneal dialysis.

RESULTS

When compared with their respective controls (pediatric median = 25.3 ng/ml, adult = 72.9 ng/ml), hepcidin was significantly increased in PCKD2-4 (127.3 ng/ml), ACKD2-4 (269.9 ng/ml), and PCKD5D (652.4 ng/ml). Multivariate regression analysis was used to assess the relationship between hepcidin and indicators of anemia, iron status, inflammation, and renal function. In PCKD2-4 (R(2) = 0.57), only ferritin correlated with hepcidin. In ACKD2-4 (R(2) = 0.78), ferritin and soluble transferrin receptor were associated with hepcidin, whereas GFR was inversely correlated. In PCKD5D (R(2) = 0.52), percent iron saturation and ferritin were predictors of hepcidin. In a multivariate analysis that incorporated all three groups (R(2) = 0.6), hepcidin was predicted by ferritin, C-reactive protein, and whether the patient had stage 5D versus stages 2 to 4 CKD.

CONCLUSIONS

These findings suggest that increased hepcidin across the spectrum of CKD may contribute to abnormal iron regulation and erythropoiesis and may be a novel biomarker of iron status and erythropoietin resistance.