Primary Cause of Anemia in Chronic Kidney Disease

Pathophysiology of Anemia in CKD

The primary cause of anemia in patients with Chronic Kidney Disease (CKD) is insufficient production of erythropoietin (EPO) by the diseased kidneys, according to the American Journal of Kidney Diseases 1, 2
Normocytic, normochromic anemia is present in the majority of patients with reduced kidney function, as reported by the American Journal of Kidney Diseases 1
As kidney function declines, the likelihood of anemia associated with EPO deficiency increases because the diseased kidneys are unable to produce sufficient quantities of EPO, as noted by the American Journal of Kidney Diseases 3, 4
Anemia can develop relatively early in the course of CKD, with significant anemia noted when GFR falls below 20-35 mL/min/1.73 m², according to the American Journal of Kidney Diseases 4

Iron deficiency, related to blood loss from laboratory testing, dialysis, or gastrointestinal bleeding, is a contributing factor to anemia in CKD patients, as reported by the American Journal of Kidney Diseases 1, 3
Severe hyperparathyroidism is a contributing factor to anemia in CKD patients, according to the American Journal of Kidney Diseases 1
Acute and chronic inflammatory conditions are contributing factors to anemia in CKD patients, as noted by the American Journal of Kidney Diseases 1
Aluminum toxicity is a contributing factor to anemia in CKD patients, according to the American Journal of Kidney Diseases 1
Folate deficiency is a contributing factor to anemia in CKD patients, as reported by the American Journal of Kidney Diseases 1
Shortened red blood cell survival is a contributing factor to anemia in CKD patients, according to the American Journal of Kidney Diseases 1
Hypothyroidism is a contributing factor to anemia in CKD patients, as noted by the American Journal of Kidney Diseases 3
Hemoglobinopathies such as thalassemia are contributing factors to anemia in CKD patients, according to the American Journal of Kidney Diseases 1

When untreated, anemia of CKD is associated with numerous physiologic abnormalities, including decreased tissue oxygen delivery and utilization, increased cardiac output and cardiac enlargement, ventricular hypertrophy, angina and congestive heart failure, decreased cognition and mental acuity, and impaired immune responsiveness, as reported by the American Journal of Kidney Diseases 1, 2

Failing to distinguish between anemia of CKD and anemia of chronic disease, where inflammatory cytokines suppress EPO production and erythropoiesis directly, is a common pitfall, according to the American Journal of Kidney Diseases 4
Not investigating other potential causes of anemia before attributing it solely to CKD is a common pitfall, as noted by the American Journal of Kidney Diseases 3

Specialized interstitial cells in the kidney cortex are responsible for sensing tissue oxygenation and producing erythropoietin in response to hypoxia 5
As kidney function declines, these cells become impaired, leading to erythropoietin deficiency and subsequent apoptotic collapse of early erythropoiesis 6
The binding of erythropoietin to receptors on erythroid colony-forming units (CFU-Es) normally salvages these cells from programmed cell death, permitting cell survival and division 5
Without adequate erythropoietin, early erythroblasts succumb to apoptosis, resulting in decreased red blood cell production 6

Inflammation in CKD patients stimulates hepatic release of hepcidin, which blocks iron absorption in the gut and iron release from macrophages 6
This leads to decreased transferrin saturation and promotes iron-deficiency erythropoiesis, even when total body iron stores may be adequate 6

Inflammatory cytokines inhibit erythropoietin production and directly impair growth of early erythroblasts 6
In the absence of adequate erythropoietin, inflammatory cytokines promote death of immature erythroblasts through ligand-mediated destruction 6
The anemia of inflammation is characteristically hypoproliferative and often includes features of iron-deficiency erythropoiesis 6

Folate and vitamin B12 deficiencies impair DNA synthesis in rapidly dividing erythroblasts, leading to apoptosis 5
Ongoing deficiencies result in disordered DNA synthesis, maturation arrest, and ineffective early erythropoiesis, typically causing macrocytic anemia 6
Iron deficiency affects the later Hb-building steps of erythropoiesis, slowing both heme and globin synthesis 6

The Kidney International guidelines suggest that multiple additional mechanisms contribute to anemia in CKD, beyond EPO deficiency 8

The Kidney International guidelines recommend established treatment paradigms using erythropoiesis-stimulating agents (ESAs) and iron supplementation for anemia in CKD, with the goal of using the lowest dose sufficient to reduce transfusion needs rather than normalize hemoglobin 8
The Kidney International guidelines also mention that newer hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHIs) offer oral administration and may improve iron utilization, particularly in inflammatory states, though long-term safety data remain limited 8

Anemia prevalence increases dramatically as GFR falls below 60 mL/min/1.73 m² (CKD stage 3), with a prevalence of 5-7.5% at CKD stage 3, 22-27% at CKD stage 4, and 33-52% at CKD stage 5, according to the American Journal of Kidney Diseases 9, 10, 11
The National Kidney Foundation recommends screening hemoglobin at least annually in all CKD patients regardless of stage, with more frequent monitoring warranted in diabetic patients who develop anemia earlier and more severely 10, 12
The American Journal of Kidney Diseases notes that patients with diabetes develop anemia at earlier CKD stages and have 2-3 times higher anemia prevalence at any given GFR level compared to non-diabetic patients 9, 10
Among kidney transplant recipients, 60% with serum creatinine >2 mg/dL are anemic compared to only 29% with creatinine <2 mg/dL, as reported by the American Journal of Kidney Diseases 11, 13