Anemia and the heart in chronic kidney disease

Cardiovascular disease is highly prevalent at all stages of chronic kidney disease (CKD) and is the leading cause of morbidity and mortality. Individuals with CKD commonly have multiple risk factors for the development of cardiovascular disease, including both traditional and nontraditional risk factors. Anemia is a nontraditional cardiovascular risk factor found in CKD that contributes to the development and progression of structural abnormalities of the heart, namely left ventricular hypertrophy and dilation. In addition, a deficiency of erythropoietin per se also may have important pathophysiologic consequences. In this review we summarize the evidence from observational studies showing an association between anemia and adverse cardiac outcomes at all stages of CKD. In addition, we provide an overview of the evidence accumulating from randomized controlled trials conducted in both nondialysis and dialysis CKD populations evaluating the effect of anemia correction on cardiac outcomes such as changes in left ventricular hypertrophy.     

Anemia in children with chronic kidney disease

Anemia in children with chronic kidney disease (CKD) is common secondary to inadequate erythropoietin production, iron deficiency, blood loss, inflammation, secondary hyperparathyroidism, uremic toxins, and nutritional deficiencies. Anemia has a variety of deleterious consequences, including associations with increased mortality and left ventricular hypertrophy. Recombinant human erythropoietin is effective in treating anemia in children with CKD, and recent studies show that darbepoetin alpha is an attractive alternative because it requires less frequent injections. Iron deficiency is a major cause of anemia that is resistant to erythropoietin or darbepoetin alpha. Although oral iron is effective in some patients, many children, especially those receiving hemodialysis, require intravenous iron to replenish their iron stores. Both acute dosing and chronic dosing of intravenous iron are effective in pediatric patients.     

Target hemoglobin in patients with renal failure

15 years after recombinant erythropoietin (EPO) has become available for the treatment of renal anemia, the target hemoglobin concentration to be achieved is still controversial. A positive impact of partial correction of renal anemia on quality of life has been conclusively demonstrated. Several more recent studies indicate that further improvement of well-being can be achieved with normalization of hemoglobin levels. In addition, there is increasing evidence that anemia is associated with the progression of left-ventricular hypertrophy and mortality. These findings imply that correction of renal anemia has the potential to improve patient prognosis. However, in patients with advanced cardiac disease, the US normal hematocrit failed to demonstrate a prognostic benefit and instead suggested that the attempt to normalize hemoglobin may be harmful. Nevertheless, in patients with less advanced cardiac disease complete correction of renal anemia may prevent progressive ventricular dilatation. The impact of early anemia correction is currently tested in several trials in predialysis patients. Irrespective of the uncertainties about the upper target range, current US and European guidelines have defined a hemoglobin concentration of 11 g/dl as the lower target range on the basis of both symptomatic and prognostic considerations. In the majority of patients these minimum requirements are not yet achieved. Less then 10% of patients receive EPO prior to the onset of dialysis, the mean hemoglobin level at the start of dialysis is not higher than 9 g/dl and a significant proportion of patients permanently remain below 11 g/dl.     

Anemia as a risk factor for chronic kidney disease

Chronic kidney disease (CKD) is an important and leading cause of end-stage renal disease (ESRD) and moreover, plays a role in the morbidity and mortality due to cardiovascular disease, infection, and cancer. Anemia develops during the early stages of CKD and is common in patients with ESRD. Anemia is an important cause of left ventricular hypertrophy and congestive heart failure. Correction of anemia by erthyropoiesis-stimulating agent (ESA) has been shown to improve survival in patients with congestive heart failure. Anemia is counted as one of the non-conventional risk factors associated with CKD. Hypoxia is one of the common mechanisms of CKD progression. Treatment by ESA is expected to improve quality of life, survival, and prevent the CKD progression. Several clinical studies have shown the beneficial effects of anemia correction on renal outcomes. However, recent prospective trials both in ESRD and in CKD stages 3 and 4 failed to confirm the beneficial effects of correcting anemia on survival. Similarly, treatment of other risk factors such as hyperlipidemia by statin showed no improvement in the survival of dialysis patients. Given the high prevalence of anemia in ESRD and untoward effects of anemia in CKD stages 3 and 4, appropriate and timely intervention on renal anemia using ESA is required for practicing nephrologists and others involved in the care of high-risk population. Lessons from the recent studies are to correct renal anemia (hemoglobin <10 g/dl not hemoglobin > or =13 g/dl). Early intervention for renal anemia is a part of the treatment option in the prevention clinic. In this study, clinical significance of anemia management in patients with CKD is discussed.     

Cardiovascular disease in patients with chronic kidney disease

Cardiovascular disease (CVD) is the major cause of morbidity and mortality in patients with renal failure. Patients with chronic kidney disease have significant CVD, and carry a high cardiovascular burden by the time they commence renal replacement therapy (RRT). The severity of CVD that has been observed in dialysis patients lead to a growing body of research examining the pathogenesis and progression of CVD during the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD) (ie, predialysis phase). Multiple factors are involved in the development of CVD in CKD. More importantly, critical and key factors seem to develop early in the course of CKD, and result in preventable worsening of CVD in this patient population. Anemia is common in patients with CKD, and has been shown to have an independent role in the genesis of left ventricular hypertrophy (LVH) and subsequent CVD. Unfortunately, it is underdiagnosed and undertreated in patients with CKD. Early intervention, and better correction of anemia, seems to gain a great momentum in the prevention and management of CVD in CKD. Hypertension is another risk factor that has been targeted by the National Kidney Foundation Task Force on CVD in chronic kidney disease. This article reviews the different factors involved in the pathogenesis of CVD in CKD and the evidence supporting early and aggressive intervention.     

Recurrence of left ventricular hypertrophy following cessation of erythropoietin therapy

The high cardiac output state is considered a major factor for occurrence of left ventricular hypertrophy (LVH). Increased left ventricular mass is a powerful predictor of morbidity and mortality. We analyzed morphologic changes of the heart in dialysis patients during treatment with erythropoietin (EPO) and after cessation of therapy. Fourteen hemodialysis patients were treated with EPO for 1 year. They were above age 18, dialyzed 3 times per week, and with a hematocrit below 28 vol%. EPO was given subcutaneously, at a dose of 20 U/kg body weight 3 times per week, before each hemodialysis session. Anemia was corrected and hematocrit maintained between 30 and 35 vol%. When this part of the study was completed, EPO was stopped in all 14 patients. Echocardiography was performed three times: at baseline, at 12 months of therapy, and 1 year after EPO cessation. Mean hematocrit of the group at these 3 time intervals was 23.78 +/- 2.11 vol%; 33.14 +/- 1.95 vol%; and 25.93 +/- 5.23 vol%, respectively (mean +/- SD). The following echocardiographic changes occurred. End-diastolic volume decreased from 134.8 +/- 25.4 to 113.2 +/- 26.4 ml and increased back to 136.2 +/- 46.2 ml. Left ventricular mass decreased from 296.6 +/- 62.4 to 225.2 +/- 52.7 g and increased again to 311.7 +/- 106 g. Cardiac output decreased from 7,295.8 +/- 2,166.9 to 5,816.4 +/- 1,216.2 ml/min and increased to 6,803.2 +/- 1,646.5 ml/min. Total peripheral resistance increased from 1,360.8 +/- 428 to 1,691.3 +/- 326 and decreased again to 1,242.8 +/- 303.3 dyne x s/cm5. All these changes were significant. Mean arterial pressure increased from 114.7 +/- 13.9 to 119.3 +/- 13.8 mm Hg and decreased to 100.5 +/- 9.3 mm Hg. LVH could be affected severely by the degree of anemia in uremics and was reversible.     

THE CLINICAL EPIDEMIOLOGY OF CARDIOVASCULAR DISEASES IN CHRONIC KIDNEY DISEASE: Hemodynamic Cardiovascular Risk Factors in Chronic Kidney Disease: What are the Effects of Intervention?

Left ventricular (LV) volume and pressure overload occur frequently in chronic kidney disease (CKD). Anemia is a risk factor for left ventricular hypertrophy (LVH) and dilatation, heart failure, and death. Normalization of hemoglobin with erythropoietin may prevent LVH and dilatation in CKD, but in patients in later phases of their cardiac disease, this intervention is not of benefit. Increased vascular volume causes hypertension, which in turn causes LVH, cardiac failure, and ischemic heart disease (IHD). Manifestations of arteriosclerosis are associated with adverse cardiac outcomes, and angiotensin converting enzyme (ACE) inhibitors may improve LVH and markers of arteriosclerosis. Aortic stenosis in dialysis patients occurs infrequently, but may deteriorate rapidly. The hemodialysis milieu is the quintessential model of LV overload cardiomyopathy.     

Effect of erythropoietin therapy on red cells filterability and left ventricular mass in predialysis patients

BACKGROUND: Cardiovascular complications are the leading cause of mortality in patients with end-stage renal disease. Left ventricular hypertrophy (LVH) is recognized as an independent risk factor for cardiovascular morbidity and mortality. At the onset of dialysis, more than 70% of the patients with chronic kidney disease have echocardiographic evidence of LVH. Anemia, increased red cells filterability time (RCFT), and blood viscosity are known to induce LVH. AIM: To evaluate, prospectively, the effects of erythropoietin (EPO) therapy for 20 weeks on RCFT and left ventricular mass (LVM). PATIENTS AND METHODS: Twenty uremic and anemic predialysis patients with creatinine clearance test below 35 mL/min were studied. RCFT test and three-dimensional echocardiography were performed at 0, 10, and 20 weeks. RESULTS: EPO therapy for 20 weeks did not adversely affect renal function and did not significantly change the mean blood pressure. It significantly increased the hemoglobin and fibrinogen levels, and decreased RCFT and LVM (p < .01). CONCLUSION: Although correction of anemia can contribute to regression of LVM, we speculate that an increasing number of cells with normalized viscoelastic properties and a direct effect of EPO on erythrocytes and myocardiocytes, through specific receptors, may also play an important role.     

The interaction between heart failure and other heart diseases, renal failure, and anemia

Anemia, defined as a hemoglobin level of less than 12 g/dL, often is seen in congestive heart failure (CHF). It is associated with an increased mortality and morbidity and increased hospitalizations. Compared with nonanemic patients the presence of anemia also is associated with worse cardiac clinical status, more severe systolic and diastolic dysfunction, a higher beta natriuretic peptide level, increased extracellular and plasma volume, a more rapid deterioration of renal function, a lower quality of life, and increased medical costs. The only way to determine if anemia is merely a marker for more severe CHF or actually is contributing to the worsening of the CHF is to correct the anemia and see if this favorably influences the CHF. In several controlled and uncontrolled studies, correction of the anemia with subcutaneous erythropoietin (EPO) or darbepoetin in conjunction with oral and intravenous iron has been associated with an improvement in clinical status, number of hospitalizations, cardiac and renal function, and quality of life. However, larger, randomized, double-blind, controlled studies still are needed to verify these initial observations. The effect of EPO may be related partly to its nonhematologic functions including neovascularization; prevention of apoptosis of endothelial, myocardial, cerebral, and renal cells; increase in endothelial progenitor cells; and anti-inflammatory and antioxidant effects. Anemia also may play a role in increasing cardiovascular morbidity in chronic kidney insufficiency, diabetes, renal transplantation, asymptomatic left ventricular dysfunction, left ventricular hypertrophy, acute coronary syndromes including myocardial infarction and chronic coronary heart disease, and in cardiac surgery. Again, controlled studies of correction of anemia are needed to assess its importance in these conditions. The anemia in CHF mainly is caused by a combination of renal failure and CHF-induced increased cytokine production, and these can both lead to reduced production of EPO, resistance of the bone marrow to EPO stimulation, and to cytokine-induced iron-deficiency anemia caused by reduced intestinal absorption of iron and reduced release of iron from iron stores. The use of angiotensin-converting enzyme inhibitor and angiotensin receptor blockers also may inhibit the bone marrow response to EPO. Hemodilution caused by CHF also may cause a low hemoglobin level. Renal failure, cardiac failure, and anemia therefore all interact to cause or worsen each other--the so-called cardio-renal-anemia syndrome. Adequate treatment of all 3 conditions will slow down the progression of both the CHF and the chronic kidney insufficiency.     

Anemia as a risk factor for cardiovascular disease and all-cause mortality in diabetes: the impact of chronic kidney disease

Anemia is a potential nontraditional risk factor for cardiovascular disease (CVD). This study evaluated whether anemia is a risk factor for adverse outcomes in people with diabetes and whether the risk is modified by the presence of chronic kidney disease (CKD). Persons with diabetes from four community-based studies were pooled: Atherosclerosis Risk in Communities, Cardiovascular Health Study, Framingham Heart Study, and Framingham Offspring Study. Anemia was defined as a hematocrit <36% in women and <39% in men. CKD was defined as an estimated GFR of 15 to 60 ml/min per 1.73 m(2). Study outcomes included a composite of myocardial infarction (MI)/fatal coronary heart disease (CHD)/stroke/death and each outcome separately. Cox regression analysis was used to study the effect of anemia on the risk for outcomes after adjustment for potential confounders. The study population included 3015 individuals: 30.4% were black, 51.6% were women, 8.1% had anemia, and 13.8% had CKD. Median follow-up was 8.6 yr. There were 1215 composite events, 600 MI/fatal CHD outcomes, 300 strokes, and 857 deaths. In a model with a CKD-anemia interaction term, anemia was associated with the following hazard ratios (95% confidence intervals) in patients with CKD: 1.70 (1.24 to 2.34) for the composite outcome, 1.64 (1.03 to 2.61) for MI/fatal CHD, 1.81 (0.99 to 3.29) for stroke, and 1.88 (1.33 to 2.66) for all-cause mortality. Anemia was not a risk factor for any outcome in those without CKD (P > 0.2 for all outcomes). In persons with diabetes, anemia is primarily a risk factor for adverse outcomes in those who also have CKD.     

Anemia and heart failure in chronic kidney disease

Cardiovascular disease is mainly responsible for the poor long-term survival observed in chronic kidney disease (CKD) patients on dialytic treatment. Anemia is an early complication of CKD and, by inducing important cardiovascular alterations, first of all left ventricular hypertrophy, it does not only impair quality of life, but has also been shown to be an independent risk factor for adverse cardiovascular outcomes in CKD patients. Clinical studies, although with discordant results, have shown that cardiovascular benefits, mainly in terms of left ventricular hypertrophy regression, may be achieved by a partial correction of hemoglobin levels, however, it still is unclear whether starting anemia correction in a very early phase of CKD or aiming for complete normalization of hemoglobin levels higher than the targets recommended by current guidelines may provide further cardiovascular advantages. Results of ongoing, large-scale, prospective, randomized, clinical trials therefore are awaited with much interest to clarify better which practices of anemia correction may provide the best results on the improvement of cardiovascular status and thus of long-term survival of patients with renal disease.     

Erythropoietin in heart failure

The incidence of both congestive heart failure (CHF) and end-stage renal disease both are increasing. Anemia is common in both conditions and is associated with a marked increase in mortality and morbidity in both CHF and chronic kidney insufficiency (CKI). Each of these 3 conditions can cause or worsen the other 2. In other words, a vicious circle frequently is present in which CHF can cause or worsen both anemia and CKI, in which CKI can cause or worsen both anemia and CHF, and in which anemia can cause or worsen both CHF and CKI. We have called this vicious circle the cardio renal anemia syndrome. Optimal treatment of CHF with all the recommended CHF medications at their recommended doses will, in our experience, frequently fail to improve the CHF and CKI if anemia is present and is not corrected. On the other hand, correction of the anemia with subcutaneous erythropoietin and intravenous iron has caused a great improvement in the CHF including a marked improvement in patient and cardiac function and a marked reduction in the need for hospitalization and for high-dose diuretics. It also frequently has caused renal function to improve or at least stabilize. In addition, patients' quality of life and exercise capacity also have improved with the correction of the anemia. In CKI patients, anemia also may play an important role in increasing the risk for death, coronary heart disease, stroke, and progression to end-stage renal disease. Erythropoietin may have a direct positive effect on the heart and brain unrelated to correction of the anemia by reducing cell apoptosis and by increasing neovascularization, both of which could prevent tissue damage. This could have profound therapeutic implications not only in CHF but in the future treatment of myocardial infarction, coronary heart disease, strokes, and renal failure.     

Regression of left ventricular hypertrophy in hemodialysis patients is possible

Regression of left ventricular hypertrophy in hemodialysis patients is possible. Left ventricular hypertrophy represents the major risk factor for cardiac morbidity and mortality. Therefore, their regression is mandatory. Since the causes of uremia-associated left ventricular hypertrophy are multifactorial, various therapeutic options can be considered: optimal control of arterial hypertension and volume status, optimal correction of metabolic acidosis, best possible correction of hypoalbuminemia and severe secondary hyperparathyroidism, modern pharmacotherapeutic strategy for the treatment of heart failure (use of angiotensin-converting enzyme inhibitors in combination with angiotensin II receptor blockers and beta-blockers) and total correction of renal anemia. Following the proposed therapeutic strategies we could, by using echocardiography, distinguish in 100 hemodialysis patients the following 3 groups (on the average after 1.5 years): 36 patients with initially normal left ventricular mass index (LVMI (g/m2), F < 110; M < 130) maintained normal (group 1); in 31 patients with moderately increased LVMI full regression resulted (group 2); 33 patients with severely increased LVMI (group 3) had to be further divided into 2 sub-groups: 22 patients with significant improvement of LVMI, 11 patients with no, regression. For the first time we were able to show that it is possible to maintain initially normal LVMI during long-term treatment and to achieve complete regression and significant improvement of LVMI in our patients. However, since LVMI requires a long time to develop, a similarly long time must be estimated for its regression. However, 11 patients remained therapeutically resistant. In this group, severe heart diseases were often combined and highly prevalent, including ischemic heart and valve diseases and end-stage dilatative cardiomyopathy. These patients had to be transferred to cardiac surgery. Anemia is considered to be one of the most important factors for the development of left ventricular hypertrophy. Therefore, total correction of renal anemia has to be strongly recommended in addition to other measures of our therapeutic strategy to maintain full or significant regression of left ventricular hypertrophy.     

Anemia in diabetes: marker or mediator of microvascular disease?

Anemia is a common finding in patients with diabetes due to the high burden of chronic kidney disease in this population. Anemia is more prevalent and is found earlier in patients with diabetes than in those with kidney disease from other causes. The increased risk of anemia in diabetes probably reflects changes in the renal tubulointerstitium associated with diabetic kidney disease, which disrupt the delicate interaction between interstitial fibroblasts, capillaries and tubular cells required for normal hemopoietic function. In particular, the uncoupling of the hemoglobin concentration from renal erythropoietin synthesis seems to be the key factor underlying the development of anemia. Systemic inflammation, functional hematinic deficiencies, erythropoietin resistance and reduced red cell survival also drive anemia in the setting of impaired renal compensation. Although anemia can be considered a marker of kidney damage, reduced hemoglobin levels independently identify diabetic patients with an increased risk of microvascular complications, cardiovascular disease and mortality. Nevertheless, a direct role in the development or progression of diabetic complications remains to be clearly established and the clinical utility of correcting anemia in diabetic patients has yet to be demonstrated in randomized controlled trials. Correction of anemia certainly improves performance and quality of life in diabetic patients. In the absence of additional data, treatment should be considered palliative, and any functional benefits must be matched against costs to the patient and the health system.     

Echocardiographic findings in hemodialysis patients treated with recombinant human erythropoietin: proposal for a hematocrit most beneficial to hemodynamics

We investigated the hemodynamic effects of the correction of anemia with recombinant human erythropoietin (rHuEPO) in 28 hemodialysis patients with severe anemia. Echocardiograms were recorded before the administration of rHuEPO (period I) with a hematocrit of 19.2 +/- 1.5% (mean +/- SD) and repeated twice (periods II and III) when the hematocrit was increased to 25.7 +/- 1.1% and to 30.0 +/- 1.0%. Left ventricular end-diastolic dimension (LVDd) decreased from 51.0 +/- 6.1 to 48.8 +/- 5.8 and to 48.3 +/- 7.1 mm, but no changes were observed in left ventricular end-systolic dimension. Cardiac output (CO) decreased from 5.89 +/- 1.46 to 5.00 +/- 1.44 and to 4.67 +/- 1.33 l/min. The thickness of the interventricular septum and the left ventricular posterior wall remained unchanged. Blood pressure was kept rather constant, although antihypertensive therapy needed to be adjusted to prevent the occurrence or aggravation of hypertension. Total peripheral resistance increased from 1481 +/- 359 to 1832 +/- 487 and to 1946 +/- 493 dynes.sec/cm5. The decreases in LVDd and CO were significant between periods I and II, without further changes between periods II and III. More antihypertensive therapy was needed in period III than in period II. Similar echocardiographic results were observed in 10 patients in whom antihypertensive therapy was not required throughout the study. In conclusion, an increase in hematocrit to 25% would be appropriate in order to obtain an effective hemodynamic improvement with rHuEPO therapy in dialysis patients although a higher hematocrit level might be desirable in order to improve working capacity.     

Anemia management in chronic heart failure: lessons learnt from chronic kidney disease

The importance of anemia in chronic kidney disease (CKD) has become increasingly well recognized over recent years, as have the benefits of treating anemic CKD patients with recombinant human erythropoietin (rHuEPO, epoetin). As well as reducing the need for blood transfusions and the complications associated with renal failure in CKD patients, rHuEPO treatment decreases patient morbidity and mortality, particularly as a result of cardiovascular disease. The strong correlation between anemia, renal failure and cardiac failure is one that has received much attention recently, with each factor recognized to cause the other to worsen in a 'vicious cycle'. Recent studies have concentrated on the possible benefits of anemia treatment in patients with CHF. Currently available data suggest improvements in CHF symptoms, left ventricular ejection fraction (LVEF) and a reduction of hospitalizations associated with anemia correction through epoetin treatment. Available data from CKD patients suggest that anemia management should begin as early as possible, although the optimal target level for individual patients is as yet unclear. In addition to the currently available evidence, additional large, randomized, controlled studies are required to further define the morbidity/mortality benefits of epoetin treatment in CHF patients with anemia.     

Cardiovascular effects of erythropoietin and anemia correction

Although recombinant erythropoietin has no short-acting pressor effect in vivo, its long-term administration frequently raises arterial pressure in humans and animals, with renal insufficiency. Contrary to the original view, erythropoietin-induced hypertension is not due to amelioration of anemia, because a similar rise in blood pressure occurs, despite persistent anemia, in erythropoietin-treated iron-deficient animals and humans. Moreover, multiple small blood transfusions administered to simulate the action of erythropoietin fail to increase blood pressure. Finally, iron repletion in severely anemic iron-deficient patients maintained on constant erythropoietin dosages does not raise blood pressure, despite a dramatic increase in hematocrit. Thus, chronic erythropoietin administration results in a hematocrit-independent, vasoconstriction-dependent hypertension that is marked by, and largely due to, elevated resting and agonist-stimulated cytoplasmic calcium concentration, leading to resistance to the vasodilatory action of nitric oxide. In addition, increased endothelin production, upregulation of tissue (but not circulating) renin and angiotensinogen expression, and a possible change in vascular tissue prostaglandin production have been variably demonstrated with erythropoietin administration in humans, intact animals and cultured endothelial cells. Erythropoietin has been shown to promote angiogenesis and stimulate endothelial and vascular smooth muscle cell proliferation. Finally, partial correction of anemia with erythropoietin therapy may partly prevent or reverse left ventricular hypertrophy in dialysis-dependent and dialysis-independent patients with chronic renal insufficiency. However, data on the risks and benefits of complete correction of anemia in this population are limited and inconclusive, and await future investigation.     

The clinical efficacy of higher hematocrit levels in children with chronic renal insufficiency and those undergoing dialysis

The optimal hematocrit target range in children with end-stage renal disease, who are receiving recombinant human erythropoietin, is ambiguous due to the lack of compelling, age-appropriate studies. There are a large number of adult and pediatric studies which show that physical performance as well as morbidity and mortality are positively influenced by partial normalization of the hematocrit to 30 vol% to 36 vol%. Cognition studies performed in adults similarly show improvement with partial correction of hematocrit. Normalization of hematocrit studies show lower mortality rates, incremental further improvement in cognition, and greater resolution of cardiac anomalies when compared with patients with partial correction of anemia. Conversely, cardiac death rates may increase in adult patients receiving hemodialysis with preexisting cardiac disease, and there are concerns about the effect of recombinant human erythropoietin on catheter/shunt/fistula patency and on blood pressure. The high cost of recombinant human erythropoietin and established Medicare and Dialysis Outcomes Quality Initiative target hematocrit ranges have also influenced pediatric nephrologists in their assessment of the risk-benefit ratios, despite new adult data suggesting that maintenance of higher hematocrits may be cost-effective. The rationale of using adult-derived hematocrits in children with end-stage renal disease needs to be re-examined in the context of the unique growth and developmental requirements of children. A prospective, multicenter study which determines the relative benefits and risks of age-adjusted hematocrit normalization in children with renal failure is warranted.     

Anemia as a risk factor for cardiovascular disease

In the present review we examine the physiologic response to chronic anemia and describe potential adverse effects of anemia on myocardial and large arterial remodeling. We present observational data demonstrating that anemia is a risk factor for cardiovascular disease (CVD) outcomes in patients with chronic kidney disease and patients with heart failure. We also present data that have evaluated the relationship of level of hematocrit to CVD outcomes in patients with ischemic heart disease and in patients in the general population. The results from the latter studies have been inconclusive and have been limited by lack of knowledge of the cause of anemia. This is potentially important because iron deficiency anemia may, in fact, improve endothelial function. We conclude that additional randomized controlled trials of treatment of anemia are needed in chronic kidney disease and patients with heart failure; however, further exploration of the cause of anemia and the effect of different types of anemia on various CVD outcomes are needed in patients with ischemic heart disease and patients in the general population.     

The high prevalence of anemia in diabetes is linked to functional erythropoietin deficiency

Anemia is a common finding in diabetes, particularly in patients with albuminuria or renal impairment. We recently showed that at least 1 in 5 outpatients with type 1 or type 2 diabetes in tertiary clinics have anemia, in whom it constitutes a significant additional burden. Anemia is associated strongly with an increased risk of diabetic complications including nephropathy, retinopathy, and heart failure. Although a number of factors contribute to an increased prevalence of anemia in diabetes, an uncoupling of hemoglobin concentration and renal erythropoietin synthesis associated with tubular dysfunction appears to be the dominant factor. In our patients with diabetes and anemia, more than three quarters had functional erythropoietin deficiency. This association was most pronounced in patients with renal impairment, in whom nearly half of all patients had anemia. However, 70% of anemic patients without renal impairment also had inappropriately low erythropoietin levels. Consequently, the likelihood of functional erythropoietin deficiency, as a cause of anemia in patients with diabetes, is not dependent on the severity of renal impairment. Although there is a clear rationale for correction of anemia in diabetes, it remains to be established whether this will lead to improved outcomes. Some small studies suggest improvement in cardiac outcomes and hospitalization. It is anticipated that large ongoing studies will help define the optimal approach to the management of anemia in diabetes.