Renal anemia

Definition

Renal anemia is a hypoproliferative, usually normochromic-normocytic anemia in chronic kidney disease. It results mainly from reduced renal production of erythropoietin (EPO) or a diminished marrow reaction to the hormone; further factors contribute.

Occurrence & epidemiology

Anemia is characteristic of moderate to advanced chronic kidney disease from stage 3 onwards. It occurs when creatinine clearance falls below about 45 ml/min. The degree of EPO deficiency and anemia does not always correlate with the degree of renal impairment: glomerular diseases, such as amyloidosis or diabetic nephropathy, are usually associated with the most severe anemia relative to the loss of function, polycystic kidney disease with a milder one.

Aetiopathogenesis

• EPO deficiency (main mechanism): with the loss of functioning renal tissue, EPO production falls relative to the hemoglobin level. EPO deficiency also reduces production of erythroferrone; hepcidin suppression is lost and iron is retained in the stores – as in anemia of inflammation.
• Reduced marrow sensitivity to EPO; secondary hyperparathyroidism also contributes.
• Shortened red cell lifespan due to uremia.
• Blood loss due to impaired platelet function and angiodysplasia.
• Coexisting deficiencies of iron, folate and vitamin B12.

Clinical features

The anemia develops slowly as kidney disease progresses and can be marked; a hematocrit of 20–30 % is typical, about 35–40 % in polycystic kidney disease. It contributes to fatigue, lassitude, reduced exercise tolerance and exertional dyspnea, which overlap with the symptoms of advanced renal failure (loss of appetite, nausea, pruritus, impaired concentration). Uremic platelet dysfunction additionally causes a bleeding tendency.

Diagnosis

• The diagnosis is based on evidence of renal insufficiency, a normocytic anemia and reticulocytopenia.
• Iron status: in chronic kidney disease, ferritin below 200 ng/ml suggests coexisting iron deficiency. A proportion of hypochromic red cells above 10 % is regarded as the best indicator of iron-deficient erythropoiesis in this setting.
• Vitamin B12 and folate to exclude further deficiencies.
• Blood smear: schistocytes – particularly with thrombocytopenia and raised reticulocytes – point to microangiopathic hemolytic anemia and require separate work-up.
• Bone marrow (rarely needed): erythroid hypoplasia.

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Further reading (open access)

1. MSD Manual Professional: Anemia of Renal Disease
2. MSD Manual Professional: Chronic Kidney Disease
3. MSD Manual Professional: Anemia of Chronic Disease
4. Onkopedia-Leitlinie (DGHO): Eisenmangel und Eisenmangelanämie (Kapitel Renale Anämie)

Cross-references