Pathophysiology of Anemia

Definition and Classification

Anemia is defined as a reduction in hemoglobin concentration, red blood cell count, or packed cell volume below normal levels (typically <13.5 g/dL in men and <12.0 g/dL in women) 2
Severity is classified as mild (Hb 10-11.9 g/dL), moderate (Hb 8.0-9.9 g/dL), or severe (Hb <8.0 g/dL) 3

Erythropoietin Deficiency: Specialized interstitial cells in the kidney cortex sense tissue hypoxia and produce erythropoietin in response; kidney disease impairs this production 4
Iron Deficiency: Iron is essential for hemoglobin synthesis; deficiency leads to microcytic anemia and is the most common nutritional cause of anemia worldwide 1
Vitamin Deficiencies: B12 and folate deficiencies impair DNA synthesis in rapidly dividing erythroblasts, leading to ineffective erythropoiesis and macrocytic anemia 4, 1
Bone Marrow Disorders: Direct infiltration by cancer cells, myelodysplastic syndromes, or radiation/chemotherapy-induced myelosuppression can reduce red blood cell production 1, 2
Inflammation-Mediated: Inflammatory cytokines (TNF-α, IL-6) cause inadequate erythropoietin production despite anemia, suppressed erythropoietic response of red cell precursors, and increased hepcidin synthesis, leading to iron sequestration and reduced iron availability for erythropoiesis 5, 6

Anemia in Chronic Heart Failure: Multifactorial etiology with prevalence ranging from 6-70% of heart failure patients, contributing factors include iron deficiency, hemodilution, inflammatory cytokine production, renal dysfunction, and medication effects 6, 5, 1
Anemia in Chronic Kidney Disease: Nearly universal in advanced CKD (stage 5), primarily caused by decreased erythropoietin production from damaged kidney cells, with additional factors including iron deficiency, shortened red cell survival, and uremic toxins suppressing erythropoiesis 1, 4
Anemia in Cancer: Multiple simultaneous mechanisms often contribute, including direct bone marrow infiltration, cytokine-mediated inflammation, chemotherapy or radiation-induced myelosuppression, nutritional deficiencies, and chronic blood loss from tumor sites 1, 8

Complete blood count with reticulocyte count to assess bone marrow response 1, 2
Peripheral blood smear examination for morphological clues 2
Iron studies (serum iron, ferritin, total iron binding capacity, transferrin saturation) 1, 2
Kidney function tests (GFR, creatinine) when renal cause is suspected 1
Vitamin B12 and folate levels 1, 2

Multiple mechanisms often contribute simultaneously to anemia, especially in complex medical conditions 1
Ferritin may be falsely elevated despite true iron deficiency in chronic inflammatory states 1
Normal hemoglobin values vary by sex, race, smoking status, and altitude 1
The combination of anemia, chronic kidney disease, and heart failure (cardio-renal anemia syndrome) has particularly poor outcomes 5