The Influence of Altitude on Erythropoietin Resistance Index in Maintenance Hemodialysis Patients: Data from Tibetan Plateau

Iron Indices Mediate but Not Modify Association of Parathyroid Hormone with Erythropoietin Resistance in Hemodialysis Patients

INTRODUCTION

Disordered iron balance and abnormal parathyroid hormone (PTH) concentrations, both prevalent in hemodialysis patients, are risk factors of erythropoietin (EPO) resistance. Few studies have evaluated the correlation between iron indices and PTH and the potential role of iron markers on the association of PTH with EPO resistance in hemodialysis population.

METHODS

In this cross-sectional study of 71 maintenance hemodialysis patients, iron indices including hepcidin, ferritin, reticulocyte hemoglobin content (CHr), and transferrin saturation (TSAT) were examined. EPO responsiveness was measured as EPO resistance index (ERI). Lowess regression curves were performed to explore the correlations of iron indices, PTH, and ERI. The association between PTH and ERI was modeled using linear regressions. Potential role of iron indices on this association was examined using stratified analyses and mediation analyses.

RESULTS

The average ERI value was 10.3 ± 5.3 IU w-1 kg-1 (g/dL) -1. ERI was correlated to PTH, hepcidin, CHr, and TSAT (all p < 0.05). Hepcidin and PTH were closely correlated with each other (r = 0.28, p = 0.020). Analysis by PTH categories yielded a total association effect of 2.53 (95% CI: 0.27-4.85, p = 0.027) for high PTH subgroup versus the reference low subgroup. No clinically significant interaction between iron indexes and PTH was identified. Hepcidin appeared to mediate about one-third of the total association between PTH and ERI in hemodialysis population (33.6%, p = 0.025).

CONCLUSION

Iron indices and PTH levels were related to ERI values. Hepcidin appeared to be closely correlated to PTH and partly mediate the association between PTH and ERI in hemodialysis population.

Relation between erythropoietin resistance and metabolic syndrome in hemodialysis patients: A multicentric propensity score matched analysis

Erythropoietin (EPO) resistance is frequently reported in hemodialysis (HD) patients. Metabolic syndrome (MetS) is a common biochemical condition that comprises central obesity, dyslipidemia, hypertension, and hyperglycemia. The present study aimed to assess the relation between MetS and EPO resistance in HD patients. The present multicentric study included 150 patients with EPO resistance and 150 patients without EPO resistance. Short-acting EPO resistance was diagnosed if the erythropoietin resistance index is ≥1.0 IU/kg/gHb. Comparison between patients with EPO resistance and patients without resistance revealed that the former group had significantly higher body mass index, lower hemoglobin levels, lower albumin levels, higher ferritin levels, and higher high-sensitivity C-reactive protein (hsCRP) levels. In addition, patients in the EPO resistance group had significantly higher frequency of MetS (75.3% vs 38.0%, p < 0.001) and higher number of MetS components (2.7 ± 1.3 vs 1.8 ± 1.6, p < 0.001). Multivariate logistic regression analysis identified lower albumin levels (OR (95% CI): 0.072 (0.016-0.313), p < 0.001), higher ferritin levels (OR (95% CI): 1.05 (1.033-1.066), p< 0.001), higher hsCRP levels (OR (95% CI): 1.041 (1.007-1.077), p = 0.018), and MetS (OR (95% CI): 36.68 (2.893-465.05), p = 0.005) as predictors of EPO resistance in the studied patients. The present study identified MetS as a predictor of EPO resistance in HD patients. Other predictors include serum ferritin, hsCRP, and albumin levels.

Effects of high altitude on renal physiology and kidney diseases

The hypobaric and hypoxic conditions of high-altitude areas exert adverse effects on the respiratory, circulatory and nervous systems. The kidneys have an abundant blood supply (20%–25% of cardiac output) and high blood flow; thus, they are susceptible to the effects of hypoxia. However, the effects of acute and chronic exposure to high altitudes on renal physiology and pathology are not fully understood. Moreover, few studies have investigated the impact of high-altitude exposure on patients with chronic kidney disease or acute kidney injury. In this review, we summarized changes in renal physiology and renal pathology due to high-altitude exposure as well as the impact of high-altitude exposure on existing kidney diseases, with the aim of informing the prevention and treatment of kidney diseases at high altitudes.