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- Anemia is a comorbidity of progressive chronic kidney disease (CKD).
- Anemia of CKD results from the inability of the kidney to produce significant quantities of erythropoietin.
- Decreased red blood cell survival and iron deficiency are cofactors.
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Since the initial observations by Richard Bright in 1836 on the relationship of anemia to renal inefficiency, anemia has remained as an ever-present comorbidity of progressive chronic kidney disease (CKD). The Kidney Disease Outcomes Quality Initiatives (K/DOQI) clinical practice guidelines for chronic kidney disease first published in 2002 helped focus attention on chronic kidney disease and its comorbidities, specifically anemia.
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Recent data support the direct relationship of anemia to cardiovascular disease and to patient mortality in end-stage renal disease (ESRD). Anemia of CKD is generally caused by the inability of the kidneys to produce significant quantities of erythropoietin, but other factors are frequently involved including decreased red blood cell survival and iron deficiency. Despite the clinical introduction of recombinant human erythropoietin (rHuEPO) in 1989, there is still an estimated 1.5 million individuals with anemia in the United States. Additionally, anemia (hemoglobin <12 mg/dL) is present in greater than 75% of dialysis patients.
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The availability of rHuEPO revolutionized our understanding of uremia and quickly became a major tool in the armamentarium of nephrologists to improve symptoms previously thought to be due to the “uremic syndrome.” Correction of anemia in these patients resulted in an improved sense of well being, improved energy levels, a significant improvement in sleep disturbances, improved cognitive function, and an improvement in the ability to perform tasks of daily living. More significantly, improved hemoglobin levels in CKD patients have been correlated with decreased left ventricular hypertrophy (LVH) and improved cardiovascular outcomes.
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Although debate continues on the proper “target” hemoglobin, the days of accepting hemoglobins less than the K/DOQI guideline recommended of 11–12 g have passed. Clinical research identifying cardiovascular events as a leading cause of mortality in CKD, ESRD, and transplant patients has made a critical understanding of the management of anemia essential to the practice of nephrology.
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Under normal homeostatic conditions, the kidney very precisely regulates plasma volume through the reabsorption or excretion of salt and water. Hemoglobin levels are maintained in response to the production of erythropoietin to tissue hypoxia.
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Erythropoietin is known to be a multifunctional tropic factor with effects on not only the bone marrow but on the central nervous system where studies have shown both neurotrophic and neuroprotective functions. Its primary target although is the pluripotent hematopoietic stem cells of the bone marrow. This cell line is capable of forming erythrocytes, leukocytes, and megakaryocytes. Erythropoietin is produced by specialized fibroblasts in the interstitium of the kidney in response to hypoxia (Figure 18–1).
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