Diabetes is the leading cause of chronic kidney disease (CKD) and is associated with
excessive cardiovascular morbidity and mortality (1,2). Anemia is common among those
with diabetes and CKD and greatly contributes to patient outcomes (3,4). Observational
studies indicate that low Hb levels in such patients may increase risk for progression
of kidney disease and cardiovascular morbidity and mortality (5). Controlled clinical
trials of anemia treatment with erythropoietin stimulating agents (ESAs) demonstrated
improved quality of life (QOL) but have not demonstrated improved outcomes (6
–10). In some trials, ESA treatment for high Hb levels is associated with worse outcomes
such as increased thrombosis risk (6,11). Consequently, the U.S. Food and Drug Administration
(FDA) and the National Kidney Foundation (NKF) have modified their recommendations
regarding anemia treatment for CKD patients (12). The objectives of this review are
to 1) update clinicians on the prevalence, causes, and clinical consequences of anemia;
2) discuss the benefits and risks of treatment; and 3) provide insight into anemia
management based on clinical trial evidence in patients with diabetes and kidney disease
who are not on dialysis.
DEFINITION AND PREVALENCE OF ANEMIA IN CKD
The NKF defines anemia in CKD as an Hb level <13.5 g/dl in men and 12.0 g/dl in women
(13). This definition is based on the fact that these levels are outside the 95% CIs
of the mean for normal men and women. Anemia is common in diabetic patients with CKD
(5). It is estimated that one in five patients with diabetes and stage 3 CKD have
anemia, and its severity worsens with more advanced stages of CKD and in those with
proteinuria (7,14,15) For example, in a 5-year prospective observational study conducted
in a diabetes clinic in Australia, anemia was found in early kidney disease, and declining
Hb levels were more common among those with higher levels of albuminuria (16) The
distribution of Hb in patients with diabetes and CKD is similar to that in those without
diabetes, but on average, Hb levels are lower. For these reasons, it is recommended
that clinicians measure serum creatinine and urine albumin and creatinine to estimate
glomerular filtration rate (GFR) and identify and quantitate albumin excretion rate
in patients with diabetes and anemia patients.
CAUSES OF ANEMIA
Anemia in diabetic patients with CKD may result from one or more mechanisms. Vitamin
deficiencies such as folate and B12 are relatively uncommon, and clinical practice
guidelines do not recommend routine measurement of these serum levels. (See below.)
The major causes of anemia in CKD patients are iron and erythropoietin deficiencies
and hyporesponsiveness to the actions of erythropoietin.
Iron deficiency
Iron deficiency in the general population is a common cause of anemia and is prevalent
in patients with diabetes and CKD. In these same patients, dietary deficiency, low
intestinal absorption, and gastrointestinal bleeding may result in absolute iron-deficiency
anemia. Recent analyses of the National Health and Nutrition Examination Survey IV
suggest that up to 50% of patients with CKD stages 2–5 have absolute or relative (functional)
iron deficiency (17). In CKD, both absolute and relative iron deficiency are common.
Absolute iron deficiency is defined as a depletion of tissue iron stores evidenced
by a serum ferritin level <100 ng/ml or a transferrin saturation of <20%. Functional
iron deficiency anemia is adequate tissue iron defined as a serum ferritin level ≥100
ng/ml and a reduction in iron saturation. The latter is more common and is strongly
associated with upregulation of inflammatory cytokines and impaired tissue responsiveness
to erythropoietin, which can inhibit iron transport from tissue stores to erythroblasts
(18). Increased levels of inflammatory cytokines such as interleukin-6 enhance production
and secretion of hepcidin, a hepatic protein that inhibits intestinal iron absorption
and impairs iron transport from the reticuloendothelial system to bone marrow. In
addition, erythropoietin, which normally enhances iron transport from macrophages
to the blood stream, is impaired, thereby exacerbating relative iron deficiency (19).
Erythropoietin deficiency and hyporesponsiveness
Both deficiency and hyporesponsiveness to erythropoietin contribute to anemia in diabetic
patients with CKD (15,20). The cause of erythropoietin deficiency in these patients
is thought to be reduced renal mass with consequent depletion of the hormone. Hyporesponsivness
is defined clinically as a requirement for high doses of erythropoietin in order to
raise blood Hb level in the absence of iron deficiency. It is believed to represent
impaired antiapoptotic action of erythropoietin on proerythroblasts. Possible causes
of this erythropoietin hyporesponsiveness include systemic inflammation and microvascular
damage in the bone marrow (15,20). However, some studies suggest that other factors
(i.e., autonomic failure) may play a role in impaired erythropoietin production or
secretion by failing kidneys (21).
Nephrotic syndrome
Nephrotic syndrome characterized by edema, hypoalbuminemia, dyslipidemia, and urine
protein-to-creatinine ratio ≥3 is not uncommon in patients with diabetic nephropathy
and can occur even in early stages of CKD (e.g., stages 1–2) (21,22). The mechanism
of anemia in nephrotic syndrome is complex and involves both inflammatory-mediated
mechanisms as discussed above as well as absolute iron deficiency. Iron excretion
increases in early stages of kidney disease in patients with diabetes and albuminuria
and is exacerbated by development of nephrotic-range proteinuria. In nephrotic syndrome,
many nonalbumin proteins are excreted in the urine, including transferrin and erythropoietin.
Significant losses of transferrin and erythropoietin can occur in nephrotic syndrome,
leading to both iron- and erythropoietin-deficiency–caused anemia in patients with
diabetes (23). Evidence for increased transferrin catabolism in nephrotic syndrome
may contribute to iron deficiency–caused anemia (24). Decreased erythropoietin production,
secretion, and hyporesponsiveness can contribute to anemia in nephrotic patients.
(See above.)
ACE inhibitors and angiotensin receptor antagonists
Both of these drug classes may cause a reversible decrease in Hb concentration in
patients with diabetes and CKD (25). The mechanisms by which ACE inhibitors and angiotensin
receptor blockers lower Hb include a direct blockade of the proerythropoietic effects
of angiotensin II on red cell precursors, degradation of physiological inhibitors
of hematopoiesis, and suppression of IGF-I. Long-term administration of losartan in
50- to 100-mg doses once daily in patients with diabetes and albuminuria is expected
to lower Hb by ∼1 g/dl. Importantly, this effect does not diminish the renoprotective
effect of losartan. It should be recognized that these classes of agents may induce
or worsen symptomatic anemia in nephropathy patients (26).
CONSEQUENCES OF ANEMIA
Quality of life
Anemia is an important cause of physical and mental impairments in diabetic CKD patients
including malaise, fatigue, weakness, dyspnea, impaired cognition, and other symptoms.
Clinical trials indicate that improving anemia improves cognitive function, sexual
function, general well-being, and exercise capacity and reduces the need for blood
transfusions (6,8
–10,27) There is renewed evidence of anemia in diabetes contributing to retinopathy,
neuropathy, diabetic foot ulcer, hypertension, progression of kidney disease, and
cardiovascular events (15).
Progression of kidney disease
In general, kidney disease in diabetes is progressive, and it has been hypothesized
that anemia may contribute to progression of kidney disease (7,16,28,29). Possible
mechanisms include renal ischemia caused by reduced oxygen delivery due to low Hb
and underlying heart failure. For example, anemia may worsen renal medullary hypoxia,
leading to renal interstitial injury and fibrosis (30,31). Whole animal and in vitro
studies indicate that renal hypoxia upregulates hypoxia-inducible factor-1α, a transcriptional
regulator of the erythropoietin gene as well as heme oxygenase, nitric oxide synthases,
extracellular matrix, and apoptosis genes. It is upregulated by renal hypoxia and
induces collagen gene expression in renal fibroblasts, thereby increasing interstitial
fibrosis. Anemia may also increase renal sympathetic nerve activity, resulting in
increased glomerular pressure and proteinuria (which in turn may accelerate progression
of kidney disease), and contribute to worsening kidney function by exacerbating underlying
heart failure—a common complication in patients with diabetes and kidney disease,
(29).
Early animal model studies in renal ablation, hypertension, and diabetes demonstrated
that treatment of anemia worsened systemic and glomerular hypertension and renal structural
and functional damage, suggesting that anemia may actually be renoprotective (32,33).
Recently, Nakamura et al. (34) demonstrated that administration of an erythropoietin-stimulating
agent to patients with anemia and CKD decreased urine fatty acid–binding protein—a
molecule known to be associated with increased risk for kidney disease progression—suggesting
that ESA may have a renoprotective effect independent of Hb level. However, in clinical
trials, erythropoietin has not yet been proven to slow kidney disease progression
in patients with diabetes and nephropathy. (See below.)
Cardiovascular disease
Observational studies indicate that death is five times more likely than progression
to end-stage kidney disease in patients with CKD (35). Moreover, cardiovascular disease
is the most common cause of death in patients with diabetes and CKD; and anemia appears
to be a risk multiplier for all-cause mortality among those same patients. Anemia
prevalence is up to 10-fold higher among diabetic patients with CKD and heart failure
and is a modifiable risk factor among diabetic patients (36), (37). Low Hb concentration
is an independent risk factor for left-ventricular hypertrophy, heart failure, and
cardiovascular mortality (37
–44). Heart failure is common in diabetic patients with nephropathy and may result
in reduced renal blood flow, thereby contributing to further reduction in GFR and
erythropoietin production. Also, anemia may aggravate tissue hypoxia, and subsequently
heart failure, resulting in further renal sodium retention, volume expansion, increased
venous return, and increased venomotor. For these reasons, treatment of anemia in
patients with diabetes and CKD is a proposed strategy to reduce excessive cardiovascular
morbidity and mortality. (See below.)
CLINICAL TRIALS OF ERYTHROPOIETIN-STIMULATING AGENTS
It is important to note that none of the published trials examining the safety and
efficacy of ESA for anemia treatment included a placebo control group. With one exception
(45), all study subjects (with varying Hb levels) were treated with an ESA.
RENAL OUTCOMES
Several small trials in patients with CKD, including those with diabetes, demonstrated
a beneficial effect on kidney disease progression. Kuriyama et al. (45) studied 106
patients with stage 3–4 CKD with or without anemia. Those with anemia were randomized
to ESA treatment or no treatment. The time to a doubling of serum creatinine from
baseline was the study's primary end point. They found that time to doubling of serum
creatinine was significantly longer in the treated group than in the nontreated group
and similar to that in the nonanemic control subjects (45). Gouva et al. (46) randomized
88 anemic stage 3–5 CKD patients to early versus late treatment with erythropoietin-α
to test the hypothesis that this intervention would slow the rate of progression to
end-stage renal disease (ESRD). They found that early correction of anemia was associated
with improved renal and patient survival compared with delayed treatment of anemia.
Rossert et al. performed a randomized controlled trial involving 390 patients with
stage 3–4 CKD and anemia to test the hypothesis that treatment of anemia with an ESA
to reach a higher Hb level would slow decline in kidney function. Subjects were targeted
to one of two Hb levels (13–15 or 11–12 g/dl) and followed for 12 months. Although
the decline in GFR was numerically less in the high-Hb group, this difference was
not statistically significant. Still, those randomized to the high group showed improvement
in QOL and vitality (47). However, the two largest trials to date to examine the effect
of ESA on progression of kidney disease (as a secondary outcome) did not show any
renal benefit of raising Hb to a higher level. (See below.)
CARDIOVASCULAR OUTCOMES
Roger et al. (9) conducted a prospective, randomized, open-label trial in 155 anemic
CKD patients (stage 3–4), testing the hypothesis that ESA treatment could prevent
development or progression of left-ventricular hypertrophy. Study subjects were randomized
to receive subcutaneous dosing with erythropoietin-α to achieve and maintain Hb in
the range of 9–10 or 11–13 g/dl and followed for 2 years with repeated measures of
left-ventricular structure and function. They found no difference in the primary outcome
of left-ventricular wall thickness; however, those assigned to the higher Hb arm of
the study experienced improvement in QOL. Levin et al. (8) conducted a randomized
clinical trial to test the hypothesis that prevention or correction of anemia, by
immediate versus delayed treatment with erythropoietin-α in patients with CKD, would
delay or prevent left-ventricular hypertrophy. The primary outcome was the change
in left-ventricular mass index. They randomized 176 CKD patients who had experienced
a decrease of 1 g/dl Hb in the prior year and a baseline Hb level of 11–13.5 g/dl
to treatment with epoetin-α to maintain Hb in the range of 12–14 g/dl or to maintain
a target Hb range of 9–10.5 g/dl; the subjects were followed for 24 months with repeated
measures of left-ventricular structure and function. Despite significant difference
in Hb level between groups, they found no significant difference in left-ventricular
mass index. Those assigned to higher Hb experienced improvement in QOL (Table 1).
Table 1
Randomized controlled cardiovascular outcome trials of anemia treatment with erythropoietin-stimulating
agents in patients with chronic kidney disease
N
Diabetes (%)
Study design
Stage of study population
HCT/Hb target
Follow-up (months)
Primary outcome
Results
QOL
Roger et al.
155
24–33
Open label
3–5
9–10/12–13
24
ΔLVMI
No benefit
Improved
Levin et al.
172
35–41
Open label
2–5
9–10.5/12–14
22.6
LVMI
No benefit
Improved
Singh et al.
1,432
48
Open label
4–5
11–11.5/13–13.5
16
Death or cardiovascular event
Worse in high Hb arm
No difference
Druecke et al.
603
25
Open label
4–5
11–11.5/13–15
36
Death or cardiovascular event
No benefit
Improved
Ritz et al.
176
100
Open label
Stage 1–3
13–15/10.5–11.5
18
LVH
No benefit
Improved
Mix et al.
4,000
100
Double-blind and placebo controlled
3–4
13.0/<11.0
24–48
Death or cariovascular events
Trial ongoing
Trial ongoing
HCT, hematocrit; HD, hemodialysis; LVH, left ventricular hypertrophy; LVMI, left-ventricular
mass index.
Ritz et al. randomized 172 anemic patients with type 1 or type 2 diabetes and stage
1–3 CKD to treatment with epoetin-α and a target Hb level of either 13–15 or 10.5–11.5
g/dl and followed them for 19 months. The primary outcome was the change in left-ventricular
mass index, and secondary outcomes included kidney function and QOL. There were no
significant differences in left-ventricular mass index in those randomized to the
higher target; however, QOL measures were significantly better in the higher Hb arm.
There were no differences in kidney function decline and no significant differences
in adverse events (48).
CARDIOVASCULAR EVENTS
Singh et al. (11) tested the hypothesis that a higher Hb level would reduce risk for
the composite cardiovascular outcome of stroke, myocardial infarction, heart failure,
and all-cause cardiovascular mortality among patients with various causes of CKD including
diabetes (∼46%). In this trial, the Correction of Hb and Outcomes in Renal Insufficiency
(CHOIR) trial, 1,432 patients with anemia and stage 3–4 CKD were randomized to an
Hb target of 11.5 or 13–13.5 g/dl and followed for an average of 16 months (11). During
the trial, Hb levels were significantly higher in those randomized to the higher Hb
arm. The composite event rate was higher in those assigned to the higher Hb arm; however,
there was no difference in the rate of development of ESRD. Also, in contrast to the
results of other studies, there was no improvement in QOL in those randomized to the
higher target. The authors concluded that use of a target Hb level of 13.5 g/dl (compared
with 11.3 g/dl) was associated with increased risk and no incremental improvement
in QOL. Post hoc analysis demonstrated that a higher fraction of patients in the higher
Hb arm had prior coronary events, hypertension, and dropout prior to an event or completion
of the study. In the Cardiovascular risk Reduction by Early Anemia Treatment with
Epoetin beta (CREATE), Drueke et al. (6) randomized 603 patients with stage 3–4 CKD,
from various causes including diabetes (∼25%), to early versus late treatment with
epoetin-α to test the hypothesis that a higher Hb level would reduce risk for cardiovascular
morbidity and mortality. Subjects were randomized to an Hb target range of 11–11.5
or 13–15 g/dl and followed for an average of 36 months. They found no significant
differences in the primary composite outcome, but there was a trend toward a higher
event rate in the higher Hb arm. In addition, multiple QOL measures were significantly
improved in those randomized to the higher Hb arm. In contrast to the CHOIR study,
the time to ESRD, a secondary outcome, was shorter in the higher Hb arm. Post hoc
analysis demonstrated that the study was underpowered to detect a difference in the
primary outcome variable as a result of the lower-than-expected overall event rate
in both arms of the study.
The increased risk for adverse outcomes during ESA treatment of anemia in clinical
trials of patients with CKD is not completely understood. One possibility is that
higher Hb increases risk for thrombosis. Another possibility is that those who experience
adverse cardiovascular events have higher comorbidity, are relatively resistant to
erythropoietin, and require higher doses of ESA to achieve higher Hb and that the
higher doses of ESA are vasculotoxic (49). Further studies are needed to determine
whether higher doses versus resistance to action of ESA cause harm in anemic patients
with CKD. The Trial of Reduction of End points with Aranesp Therapy (TREAT) is an
ongoing large-scale, randomized, double-blind, and placebo-controlled study including
4,000 anemic patients with type 2 diabetes and CKD (50). The primary outcome is a
composite of all-cause mortality and cardiovascular morbidity. This ongoing trial
is unique in many respects, including the double-blind, placebo-controlled design;
the population of exclusively anemic patients with type 2 diabetes and CKD; and a
large sample size. This study will add important new information concerning benefits
and risks of ESA treatment of anemia in patients with diabetes and CKD. Results are
expected in 2010.
In summary, two clear messages emerge from the anemia treatment trials. 1) Treating
patients to achieve a higher compared with a lower Hb target typically improves QOL.
2) Treatment to reach a higher Hb level does not reduce risk for cardiovascular events
and may cause harm.
CLINICAL PRACTICE GUIDELINES FOR EVALUATION OF ANEMIA
The NKF clinical practice guidelines for diagnosis and management of anemia in patients
with CKD recommend a routine history and physical examination, a complete blood count,
a reticulocyte count, evaluation of serum iron and total iron binding capacity and
serum ferritin level, and a fecal test for occult blood for evaluation of anemia (13,51).
Additional tests to evaluate anemia should be guided by this initial evaluation (e.g.,
serum folic acid, vitamin B12 level, Coombs test, etc.). Despite the high prevalence
of anemia in the CKD population, treatment with erythropoietin or iron often is not
used in the predialysis period. For example, nearly 70% of patients initiated on dialysis
are anemic by the NKF definition but are not treated with erythropoietin, and >50%
of these patients have severe anemia (hematocrit <30%).
RECOMMENDATIONS FOR TREATMENT OF ANEMIA
NKF clinical practice guidelines
The NKF currently recommends that when treating anemia in CKD with an ESA, the Hb
target range should be 11–12 g/dl and should not exceed 13 g/dl (51). In addition,
the NKF recommends that treatment should be individualized, taking into account patient
characteristics including symptoms, Hb level, and evaluation for other causes of anemia.
(See above.) If the initial evaluation indicates absolute iron deficiency as the cause,
treatment with supplemental iron and a search for the cause of iron loss should be
undertaken. If absolute iron deficiency is not present and causes other than kidney
disease are excluded, then treatment with an ESA should be administered at a dose
sufficient to increase Hb within the target range of 11–12 g/dl. Importantly, ESA-treated
patients should, in general, receive iron to ensure that adequate stores are available
for erythropoietic response (51). The NKF notes that with few exceptions, anemia treatment
trials in CKD patients demonstrated that treatment with an ESA to achieve Hb values
in the range of 11–13 g/dl is associated with improved QOL.
Food and Drug Administration
In early 2007, the Food and Drug Administration (FDA) promulgated new recommendations
for use of ESA in patients with CKD, advising them that ESA can increase risk for
heart attack, stroke, blood clots, heart failure, and death when given to maintain
higher Hb (52). Drugs affected by their recommendation included epoetin-α and darbepoetin.
The FDA advised practitioners to use the lowest dose of an ESA needed to avoid blood
transfusion, targeting blood Hb in the range of 10–12 g/dl, and to withhold the dose
of ESA when Hb level exceeds 12 g/dl. Manufacturers of ESA accordingly added black
box warnings noting these recommendations (53).
In summary, the NKF and FDA recommendations are in conflict. Whereas there is agreement
that ESAs are valuable for treating anemia, they differ with regard to the level of
Hb at which to initiate ESA and the upper limit of the Hb target. The NKF supports
the safety of ESA use and recognizes the importance of individualizing anemia treatment.
Further studies on the safety of ESA use in the diabetes population, as well as efforts
to better understand the explanation for the association of higher Hb with worse cardiovascular
outcomes reported in clinical trials, are needed.
ANEMIA MANAGEMENT
The first step in the management of anemia is evaluating the underlying cause. (See
above on diagnosis and evaluation.) If absolute iron deficiency is present, the patient
should be put on oral or intravenous iron therapy. Several oral iron preparations
are available for treatment including ferrous gluconate, fumarate, and sulfate. Doses
of 300–325 mg of one of these agents three times daily can increase the Hb level significantly
in such patients. Notably, significant gastrointestinal side effects may lead to poor
adherence and compliance with oral iron. An alternative is to administer intravenous
iron on a periodic basis. Several studies indicate that these preparations are effective
and safe in predialysis populations (11,54,55). Dahdah et al. (54) administered intravenous
iron dextran to anemic, iron-deficient (serum ferritin <100 ng/ml or transferrin saturation
<20%) patients with an estimated GFR <50 ml/min and not on dialysis in doses of either
200 mg/week for 5 weeks or 500 mg/week for 2 weeks. Significant increases in Hb occurred
within 2 weeks; all patients tolerated infusions without serious adverse reactions.
Intravenous iron preparations including ferric sodium gluconate, iron sucrose, and
iron dextran are available and can be administered safely. Among these agents, iron
dextran has been associated with the highest incidence of adverse reactions, although
the incidence of such reactions is low with all three preparations. Although some
studies indicate that intravenous iron is in general more efficacious than oral iron
for achieving increases in Hb in patients with CKD, oral iron is also effective (55).
Moreover, no definite advantages have been shown with intravenous versus oral iron
in patients with CKD not on dialysis (56).
An initial dose of 10,000 units epoetin-α once weekly or 0.75 μg/kg darbepoetin-α
every other week subcutaneously are effective for increasing Hb concentration by 1–2
g/dl over 4–8 week periods (27). Darbepoetin can be administered subcutaneously every
other week at outset and then administered once monthly to maintain Hb target. Ling
et al. (57) demonstrated efficacy of maintaining Hb in the range of 10–12 g/dl (total
dose of 88 μg) after extending the dosing interval from every other week to once every
4 weeks. Provenzano et al. (58) found that an increased dosing interval from weekly
to once monthly using epoetin-α in doses up to 40,000 units maintained Hb in a similar
range.
Extended dosing of short- and long-acting ESA, including the hematopoietic and adverse
effects, has recently been reviewed (59). Currently, the only ESA approved by the
FDA for extended interval dosing is darbepoetin. In clinical practice, darbepoetin
is often administered every other week initially, until the Hb target is achieved,
before extending dosing to every 4 weeks. Extended dosing may require an increase
in dose (27,57).
Monitoring response to treatment
Patients should be evaluated for improvement in symptoms including fatigue, vitality,
physical functioning, and cognitive function. Initially, Hb level should be measured
every other week to monitor the hematopoietic response and monthly thereafter. In
general, if an Hb level deviates from the target range (see above), the dose of the
ESA should be adjusted either upward or downward by 25%. In most patients, increases
or decreases in ESA dose should not be made more frequently than monthly. Also, for
safety reasons, if Hb is rising at a rate of >1 g/dl within a 4-week period, the dose
should be held, as more rapid increases may be associated with increased risk for
adverse events such as hypertension.
Functional iron deficiency should be suspected in any patient not responding to ESA
treatment, and patient compliance with iron therapy should be investigated. Routine
measurement of iron stores including serum iron, iron binding capacity, and ferritin
should be monitored monthly for 3 months then quarterly once Hb target is achieved
(56,60).
Adverse side effects of therapy
In clinical trials, up to 25% of patients experience an increase in blood pressure
or develop overt hypertension (blood pressure >140/90 mmHg) (8,27,47,61
–63). Thus, ESA should not be used to treat anemia in patients with uncontrolled blood
pressure. Moreover, increases in blood pressure should be looked for in any anemic
CKD patient treated with an ESA, and dose adjustments in ESA, iron, or antihypertension
medications should be undertaken as needed. Common side effects include local pain
or tissue reaction to subcutaneous injection and development of flu-like symptoms
within hours or days of administration of an ESA.
A rare but serious form of pure red cell aplasia can occur during ESA treatment, including
in those treated with epoetin and darbepoetin (64,65). The anemia is sudden in onset
and can occur as early as 2 months after initiation of treatment. As noted above,
ESA may increase risk for death and cardiovascular events and thrombotic events. The
risk is reported in those with Hb levels >12 g/dl in some clinical trials. Therefore,
it is prudent to modify the dose of ESA to reduce the likelihood of excursions of
Hb exceeding 13 g/dl as recommended by the NKF (51). Adverse effects of iron use are
described above and include gastrointestinal side effects with oral preparations and
anaphylactic reactions with intravenous preparations.
AREAS OF UNCERTAINTY
Analysis of available evidence from clinical trials clearly indicates that there is
enough uncertainty regarding the risk-to-benefit ratio of treatment of anemic CKD
patients with ESA to warrant additional major randomized clinical trials (66). TREAT
is an ongoing study that will provide additional new information on whether treatment
per se can improve cardiovascular outcomes in patients with type 2 diabetes, anemia,
and CKD (50). Because nearly 50% of new cases of ESRO in the U.S. are attributed to
diabetes, further studies are needed to help guide management of anemia. Areas of
uncertainty that remain include establishment of the optimal individual Hb level—the
level at which patient QOL is maximized and morbidity and mortality risks are minimized.
The optimal dose of a given ESA, the frequency of dosing, and the indication and target
Hb range remain controversial. For example, should ESA dosing begin at an Hb level
of 10, 11, or 12 g/dl? Another area of uncertainty concerns the diagnosis and management
of erythropoietin hyporesponsiveness, for which there is no widely accepted, standardized
definition. This confounds the analysis of clinical trials in which higher doses of
ESA and higher Hb occur in those randomized to higher Hb targets. Additional studies
are needed to understand the nature and extent of hyporesponsiveness to erythropoietin
in patients with CKD—an area of high priority for future research. However, it is
not established whether the benefits of improved QOL measures outweigh the risks of
cardiovascular morbidity and the economic costs related to treatment to achieve a
higher Hb level. Another area of uncertainty related to hyporesponsiveness is the
role of iron use in treating anemia. New research that provides a better understanding
of the role of inflammation in iron metabolism, utilization, and the response to ESA
treatment is another important research priority.
SUMMARY
Anemia is common and contributes to both poor QOL and increased risk for adverse outcomes
including death. Treatment of anemia improves QOL; however, thus far, evidence is
lacking for a benefit of anemia treatment on progression of kidney disease and cardiovascular
outcomes. The NKF recommends that physicians consider treating anemia in patients
with diabetes and kidney disease when Hb is <11 g/dl in patients. Further, they recommend
a Hb target of 11–12 g/dl, not to exceed 13 g/dl, when using an ESA as part of the
therapeutic regimen for managing anemia. Currently available ESA combined with iron
supplementation can be used safely and effectively to achieve this goal. However,
available clinical trial evidence leaves sufficient uncertainty regarding the optimal
Hb target and ESA dose for a given individual. For this reason, the NKF recommends
individualizing treatment of anemia with ESA. Additional randomized clinical trials
are needed to more precisely define these parameters for an individual patient. Future
studies are also needed to elaborate the mechanisms of anemia in patients with diabetes
and CKD including the role of iron metabolism, inflammation, and resistance.