The problem with transferrin saturation as an indicator of iron 'sufficiency' in chronic kidney disease

Transferrin levels are associated with malnutrition markers in hemodialysis patients in KwaZulu-Natal, South Africa

INTRODUCTION

Malnutrition is a global phenomenon and may be contributing to the increasing size of the hemodialysis (HD) population in South Africa and is affecting morbidity and clinical outcomes. Our study assessed whether transferrin could be a possible marker for malnutrition in the HD population.

METHODS

Clinical parameters (including skinfold thickness and mid-upper arm circumference [MUAC]) and laboratory markers (including transferrin and hemoglobin) were measured during a six-month period in a sample of 59 HD patients.

RESULTS

Linear regression analysis showed that MUAC (p = 0.027) as well as skinfold thickness (p = 0.021) had a significant association with transferrin levels within the HD participants. There was no significant association between transferrin levels or MUAC with hemoglobin levels (p = 0.075). Furthermore, the study found that decreased transferrin levels (< 2.15 g/dL to 3.80 g/dL) were closely related to malnutrition in the malnutrition distribution groups within the study, with 97.7% of HD participants being classified in one of the malnutrition groups.

CONCLUSION

Thus, transferrin levels are a valuable marker for malnutrition within the HD patient population and can be included along with clinical assessment parameters such as MUAC and skinfold thickness as primary indicators for malnutrition.

Anemia of Chronic Kidney Disease-A Narrative Review of Its Pathophysiology, Diagnosis, and Management

Anemia is one of the most common chronic kidney disease (CKD) complications. It negatively affects patients' quality of life and clinical outcomes. The pathophysiology of anemia in CKD involves the interplay of various factors such as erythropoietin (EPO) deficiency, iron dysregulation, chronic inflammation, bone marrow dysfunction, and nutritional deficiencies. Despite recent advances in understanding this condition, anemia still remains a serious clinical challenge in population of patients with CKD. Several guidelines have been published with the aim to systematize the diagnostic approach and treatment of anemia; however, due to emerging data, many recommendations vary between publications. Recent studies indicate a potential of novel biomarkers to evaluate anemia and related conditions such as iron deficiency, which is often present in CKD patients. Our article aims to summarize the pathophysiology of anemia in CKD, as well as the diagnosis and management of this condition, including novel therapeutic approaches such as hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHI). Understanding these complex subjects is crucial for a targeted approach to diagnose and treat patients with anemia in CKD effectively.

Clinical Experience of a Long-acting Pegylated Erythropoietin-Stimulating Agent in Pediatric Chronic Kidney Disease

OBJECTIVE

Management of anemia of chronic kidney disease (CKD) often includes subcutaneous or intravenous administration of erythropoietin-stimulating agents (ESAs). Mircera, a pegylated continuous erythropoietin receptor agonist, has a longer duration of action and requires less frequent administration than other ESAs. Pediatric experience with Mircera is limited. We retrospectively reviewed our long-term experience of Mircera in a national pediatric nephrology center.

METHODS

Patients were identified via an electronic patient record database. Data collected included demographics (sex, age, etiology of CKD, CKD stage, dialysis modality), dosing information, and laboratory data-hemoglobin (Hb), parathormone (PTH), ferritin, hematinics prior to commencing Mircera and all subsequent values associated with dose adjustments.

RESULTS

Seventy-seven patients aged 2 to 18 years, with CKD stages 2 to 5T had received at least 1 dose of Mircera, with 75 patients having sufficient data and a total of 1473 doses. No patients discontinued Mircera owing to adverse effects. One patient experienced a potential severe adverse drug reaction. Mircera was effective in improving or maintaining Hb ≥10.0 g/dL in most (58/75, 77.3%) patients. The median dose to achieve Hb ≥10.0 g/dL was 2.1 µg/kg/4 wk. Most doses (1039, 71.5%) were administered 4-weekly. The doses (161, 11.1%) that were administered 6-weekly remained efficacious. Thirty-two patients started Mircera with Hb <10.0 g/dL; 26 (81%) achieved Hb ≥10.0 g/dL within a median time of 4 months. Mircera was less effective if given every 8 weeks, or in the presence of hyperparathyroidism or hyperferritinemia.

CONCLUSION

Mircera appears safe and effective in pediatric patients with CKD.

The Association between Iron Deficiency and Renal Outcomes Is Modified by Sex and Anemia in Patients with Chronic Kidney Disease Stage 1–4

Iron deficiency is prevalent in women and patients with chronic kidney disease (CKD). Iron deficiency is not only related to anemia but contributes to adverse consequences for the kidney as well. Whether iron status is associated with renal outcomes after considering sex and anemia in patients with CKD stage 1–4 is unclear. Thus, we investigated the association of iron or iron saturation with renal outcomes in a CKD cohort. During a follow-up of 8.2 years, 781 (31.2%) patients met the composite renal outcome of renal replacement therapy and a 50% decline in renal function. In linear regression, iron was associated with sex, hemoglobin (Hb), and nutritional markers. In a fully adjusted Cox regression model, the male patients with normal iron had a significantly decreased risk of renal outcomes (hazard ratio (HR) 0.718; 95% confidence interval (CI) 0.579 to 0.889), but the female patients did not exhibit this association. The non-anemic patients (Hb ≥ 11 g/dL) had a decreased risk of renal outcomes (HR 0.715; 95% CI 0.568 to 0.898), but the anemic patients did not. In the sensitivity analysis, transferrin saturation (TSAT) showed similar results. When comparing iron and TSAT, both indicators showed similar prognostic values. In conclusion, iron deficiency, indicated by either iron or iron saturation, was associated with poor renal outcomes in the male or non-anemic patients with CKD stage 1–4.

Percent Body Fat-Related Disparities of Serum Ferritin on the Risk of Lipid Metabolism Abnormalities in Children and Adolescents

OBJECTIVE

This study examined the association between serum ferritin and dyslipidemia in children and adolescents with different degrees of obesity.

METHOD

In this multi-stage, stratified, randomized, sampling cross-section cohort study, demographic data were collected by questionnaire from 4320 children and adolescents (aged 6-17 years) in Shanghai, China. Anthropometric measures and percent body fat (PBF) were recorded. Serum lipid parameters were detected by an automatic biochemical method, and ferritin levels were measured by an automatic immunoassay.

RESULTS

Our results showed 70.6%, 13.9%, and 15.5% of participants had a healthy body fat, low fat, and overweight/obese, respectively. Increasing ferritin quartiles were independently associated with a greater hazard of dyslipidemia, especially in overweight/obese participants, and the OR (95% CI) was 3.01 (1.29-7.00), 3.58 (1.59-8.04), and 5.66 (2.57-12.46) across the ferritin quartiles after adjustment for confounders. Ferritin was only a predictive value for dyslipidemia in overweight/obese participants (AUC = 0.64) and was consistent in boys (AUC = 0.61) and girls (AUC = 0.68). The significant positive correlation between ferritin value and lipid abnormalities profiles (except for low HDL-C) mainly appeared in the overweight/obesity group.

CONCLUSION

The results showed that serum ferritin can be considered an independent risk factor for dyslipidemia in children and adolescents with obesity.

HIGHLIGHTS

Ferritin overload had a greater risk of dyslipidemia, especially in children and adolescents with overweight/obesity.

Individualized anemia management enhanced by ferric pyrophosphate citrate protocol

The optimal use of erythropoiesis-stimulating agents (ESAs) and parenteral iron in managing anemia in end-stage renal disease (ESRD) remains controversial. One-size-fits-all rule-based algorithms dominate dosing protocols for ESA and parenteral iron. However, the Food & Drug Administration (FDA) guidelines for using ESAs in chronic kidney disease recommend individualized therapy for the patient. This prospective quality assurance project was at a single hemodialysis (HD) center comprising three 6-month phases (A, B, C) separated by 3-month washout periods. Standard bi-weekly ESA dose titration and intravenous (IV) iron sucrose protocols were used in baseline Phase A, and ferric pyrophosphate citrate (FPC) augmented iron in Phase B. In Phase C, an FPC protocol and weekly, individualized ESA management were used. We examined clinic-level mean differences in hemoglobin (Hb) and ESRD-related outcomes by phase with repeated ANOVA. To examine the Hb at the patient level, we used multi-level mixed-effect regression adjusting for phase, month, and other relevant confounders at each month over time to derive the mean marginal effects of phase. There were 54, 78, and 66 patients in phases A, B, and C, respectively, with raw mean Hb values of 9.9, 10.2, and 10.3 g/dL. The percentage of Hb values < 9 g/dL declined from 14.3% in Phase A to 7.6% in Phase C (p = 0.007). The multivariable mixed-effect regression results showed mean marginal Hb was higher by 0.3 mg/dL and 0.4 mg/dL in Phases B and C, respectively, compared to Phase A. We also observed reduced ferritin (p = 0.003) and transferrin saturation (TSAT) (p = 0.008) levels from Phase A to Phase C with the repeated ANOVA analysis. Ferric pyrophosphate citrate (FPC) appears to support more efficient ESA-stimulated erythropoiesis. Moreover, individualized ESA management combined with FPC (Phase C) was associated with further improvement in efficiency as we observed the fewest patients with Hb values < 9 g/dL concurrent with greater decreases in ferritin levels and reduced ESA doses. However, future prospective studies to confirm these findings on a larger, more diverse cohort of ESRD patients are warranted.

Immunoaffinity Capillary Electrophoresis in the Era of Proteoforms, Liquid Biopsy and Preventive Medicine: A Potential Impact in the Diagnosis and Monitoring of Disease Progression

Over the years, multiple biomarkers have been used to aid in disease screening, diagnosis, prognosis, and response to therapy. As of late, protein biomarkers are gaining strength in their role for early disease diagnosis and prognosis in part due to the advancements in identification and characterization of a distinct functional pool of proteins known as proteoforms. Proteoforms are defined as all of the different molecular forms of a protein derived from a single gene caused by genetic variations, alternative spliced RNA transcripts and post-translational modifications. Monitoring the structural changes of each proteoform of a particular protein is essential to elucidate the complex molecular mechanisms that guide the course of disease. Clinical proteomics therefore holds the potential to offer further insight into disease pathology, progression, and prevention. Nevertheless, more technologically advanced diagnostic methods are needed to improve the reliability and clinical applicability of proteomics in preventive medicine. In this manuscript, we review the use of immunoaffinity capillary electrophoresis (IACE) as an emerging powerful diagnostic tool to isolate, separate, detect and characterize proteoform biomarkers obtained from liquid biopsy. IACE is an affinity capture-separation technology capable of isolating, concentrating and analyzing a wide range of biomarkers present in biological fluids. Isolation and concentration of target analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. IACE has the potential to generate rapid results with significant accuracy, leading to reliability and reproducibility in diagnosing and monitoring disease. Additionally, IACE has the capability of monitoring the efficacy of therapeutic agents by quantifying companion and complementary protein biomarkers. With advancements in telemedicine and artificial intelligence, the implementation of proteoform biomarker detection and analysis may significantly improve our capacity to identify medical conditions early and intervene in ways that improve health outcomes for individuals and populations.

Low serum iron is associated with anemia in CKD stage 1-4 patients with normal transferrin saturations

Low transferrin saturation (TSAT), calculated by serum iron divided by total iron-binding capacity (TIBC), indicates iron deficiency. Because malnutrition and inflammation are associated with low TIBC in chronic kidney disease (CKD), TSAT might not reflect iron status or risk for anemia. We examined whether low serum iron was a risk factor for anemia in CKD patients with normal TSAT. Thus we compare the risk for anemia in 2500 CKD stage 1–4 patients divided by TSAT (cutoff: 20%) and serum iron (cutoff: 70 μg/dL in men, 60 μg/dL in women). Our results confirmed low TIBC (< 200 μg/dL) was associated with hypoalbuminemia and high C-reactive protein. In fully-adjusted logistic regression, both “normal TSAT low iron” and “low TSAT low iron” groups were associated with baseline anemia (hemoglobin < 11 g/dL) (odds ratios (OR) 1.56; 95% confidence interval (CI) 1.13–2.16 and OR 2.36; 95% CI 1.76–3.18, respectively) compared with the reference group (normal TSAT normal iron). Sensitivity tests with different cutoffs for TSAT and iron also showed similar results. In patients without anemia, both groups were associated with anemia after 1 year (OR 1.69; 95% CI 1.00–2.83 and OR 1.94; 95% CI 1.11–3.40, respectively). In conclusion, CKD stage 1–4 patients with normal TSAT but low serum iron are still at risk for anemia.

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.

Associations of iron status with apolipoproteins and lipid ratios: a cross-sectional study from the China Health and Nutrition Survey

Background

Iron overload has been found to be related with various cardiometabolic disorders, like dyslipidemia, metabolic syndrome, and diabetes. The disturbance of the iron status and lipid metabolism can contribute to organ damage such as atherosclerotic plaque growth and instability. An assessment on the associations of iron status with apolipoproteins and lipid ratios would be informative for maintenance of metabolic homeostasis and hinderance of disease progression. Hence, this study aims to establish the relationships of iron status with apolipoproteins and lipid ratios.

Methods

A cross-sectional study of 7540 adult participants from the China Health and Nutrition Survey 2009 was conducted. Logistic regression analyses were used to investigate the relationships between indicators of iron status and the prevalence of unfavorable apolipoprotein profiles. Multivariate linear regression models were constructed to assess the dose-response correlations between serum ferritin and lipid parameters.

Results

After adjustment for confounding factors, in both sexes, the subjects in the top quartile of ferritin had the highest prevalence of an elevated apolipoprotein B (men: odds ratio (OR) 1.97, 95% confidence interval (CI) 1.50–2.62; women: OR 2.13, 95% CI 1.53–2.97) and an elevated apolipoprotein B/apolipoprotein A1 ratio (men: OR 2.00, 95% CI 1.50–2.66; women: OR 1.41, 95% CI 1.04–1.92) when compared with individuals in the lowest quartile. Hemoglobin were also independently associated with unfavorable apolipoprotein B and apolipoprotein B/apolipoprotein A1 ratio both in men and women. However, transferrin (men: OR 0.74, 95% CI 0.56–0.99; women: OR 0.73, 95% CI 0.56–0.95) and soluble transferrin receptor (men: OR 0.75, 95% CI 0.57–0.99; women: OR 0.71, 95% CI 0.55–0.91) were found to be negatively associated with a decreased apolipoprotein A1. Moreover, after controlling for potential confounders, the ferritin concentrations were significantly associated with the levels of lipid ratios including TG/HDL-C, non-HDL-C/HDL-C, TC/HDL-C, apoB/apoA1, and LDL-C/HDL-C ratio in men (β coefficient = 0.147, 0.061, 0.043, 0.038, 0.032, respectively, all P values < 0.001) and in women (β coefficient = 0.074, 0.034, 0.025, 0.020, 0.018, respectively, all P values < 0.05).

Conclusions

The indicators of iron status are significantly associated with unfavorable apolipoprotein profiles. Serum ferritin concentrations are positively correlated with the levels of lipid ratios. The management on the modifiable iron status and lipid metabolism has a clinical significance. The atherosclerotic lipid profiles of the patients with iron overload deserve special clinical concerns.