Understanding Anemia: Etiology and Pathophysiology

Definition

Anemia is a condition characterized by a lower than normal number of red blood cells (RBCs) or hemoglobin concentration within them. It is a symptom indicating an underlying condition rather than a diagnosis in itself.

Key Point

Anemia serves as a warning sign, necessitating further investigation to uncover the root cause.

Symptoms

Symptoms typically manifest when hemoglobin levels drop below 7.0 g/dL and include:

• Weakness
• Lethargy
• Shortness of breath
• Chest pain
• Bleeding

Normal Hemoglobin Ranges

• Men: 13.5 to 18.0 g/dL
• Women: 12.0 to 15.0 g/dL
• Children: 11.0 to 16.0 g/dL
• Pregnancy: Generally >10.0 g/dL, varies by trimester

Etiology of Anemia

Hypoproliferative Anemia: Characterized by a corrected reticulocyte count <2%.

• Microcytic (MCV < 80 fL): Iron deficiency, anemia of chronic disease (AOCD), sideroblastic anemia, thalassemia, lead poisoning.
• Normocytic (MCV 80-100 fL): AOCD, renal failure, aplastic anemia.
• Macrocytic (MCV > 100 fL): Alcohol use, liver disease, B12/folate deficiency, myelodysplastic syndromes (MDS).

Hyperproliferative Anemia: Corrected reticulocyte count >2%.

Hemolytic Anemia

• Extravascular Hemolysis: RBCs removed by the liver/spleen. Causes include hemoglobinopathies, enzymopathies, and drug-induced conditions.
• Intravascular Hemolysis: RBCs lyse within circulation. Causes include paroxysmal nocturnal hemoglobinuria (PNH), autoimmune hemolytic anemia (AIHA), transfusion reactions, and infections.

Epidemiology

• Prevalence: Affects up to one-third of the global population. Overall prevalence is 40.9%, higher among rural residents (46.6%) compared to urban residents (20.1%).
• At-risk Groups: Women of reproductive age, pregnant women, the elderly, and those with chronic conditions.
• Special Considerations: Higher prevalence in the elderly and those with poor nutrition.

Pathophysiology

• Production and Destruction Balance: The balance between RBC production in bone marrow and their destruction/removal.
• Mechanisms: Increased RBC destruction or deficient/defective erythropoiesis.
• Examples: Blood loss, hemolytic anemia, defects in erythropoiesis.

Clinical Presentation

• Symptoms: Weakness, lethargy, shortness of breath, chest pain, bleeding.
• Signs: Pallor, tachypnea, hypotension, splenomegaly, hepatomegaly, and neurological deficits related to vitamin B12 deficiency.

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