What are the causes of anemia?
According to the etiology, anemia can be divided into three major categories: hypoproliferative, hemorrhagic, and hemolytic.
I. Hypoproliferative Anemia (Decreased Red Blood Cell Production)
(A) Disorders of Hemoglobin Synthesis
1. Iron-deficiency anemia: Insufficient iron intake, relatively increased iron requirements (pregnancy, periods of childhood growth), impaired iron absorption (chronic gastrointestinal diseases, after subtotal gastrectomy), chronic blood loss.
2. Sideroblastic anemia.
3. Vitamin B6-responsive anemia.
4. Atransferrinemia.
(B) Nuclear Maturation Disorders
1. Pernicious anemia.
2. Megaloblastic anemia due to impaired utilization of folic acid and/or vitamin B12 from other causes: Malnutrition (deficiency in diet, improper infant feeding, chronic alcoholism, intractable anorexia), increased requirements (pregnancy, lactation, periods of childhood growth, infection with Diphyllobothrium latum, hemolysis, infection, hyperthyroidism, etc.), malabsorption (total or subtotal gastrectomy, chronic atrophic gastritis, gastric cancer, chronic liver disease, chronic enteritis, malabsorption syndrome, post-enterectomy, bacterial overgrowth in intestinal diverticula), effects of drugs on nucleic acid metabolism (e.g., antifolates, anticonvulsants, antituberculosis drugs, oral contraceptives, neomycin, nitrites, etc.).
(C) Reduced Bone Marrow Hematopoietic Function
1. Stem cell defects
(1) Aplastic anemia.
(2) Congenital aplastic anemia.
(3) Pure red cell aplasia.
(4) Myelodysplastic syndromes.
2. Bone marrow hematopoietic tissue displaced by other cells: Leukemia, malignant lymphoma, multiple myeloma, metastatic carcinoma of bone, myelofibrosis, systemic mastocytosis, osteopetrosis, etc.
3. Defects in erythropoietic regulatory factors: Renal anemia, hypofunction of endocrine glands (e.g., pituitary, thyroid), infectious anemia, etc.
II. Hemorrhagic Anemia
(A) Acute hemorrhagic anemia
Such as massive external bleeding from trauma or rupture of internal organs leading to hemorrhage, ectopic pregnancy, massive gastrointestinal bleeding, etc.
(B) Chronic hemorrhagic anemia
Such as menorrhagia, hemorrhoids, hookworm disease, gastric cancer, peptic ulcer, etc.
III. Hemolytic Anemia (Excessive Red Blood Cell Destruction)
(A) Intrinsic Defects of Red Blood Cells
1. Congenital and hereditary
(1) Red blood cell membrane abnormalities: Hereditary spherocytosis, hereditary elliptocytosis, hereditary stomatocytosis.
(2) Red blood cell enzyme abnormalities: Defects in enzymes of anaerobic glycolysis (e.g., pyruvate kinase deficiency), deficiencies in enzymes of the hexose monophosphate shunt (e.g., glucose-6-phosphate dehydrogenase deficiency, often triggered by oxidative drugs like fava beans or primaquine, or infections; other hemolytic anemias caused by deficiencies of related components).
(3) Globin chain abnormalities: Abnormalities in the quantity of polypeptide chains (alpha-thalassemia, beta-thalassemia), abnormalities in polypeptide chain structure (polymerization hemoglobinopathies, unstable hemoglobinopathies).
2. Acquired acquired Paroxysmal nocturnal hemoglobinuria (PNH).
(B) External Factors of Red Blood Cells
1. Immunological
(1) Autoimmune: Warm antibody type (acute idiopathic acquired hemolytic anemia, chronic idiopathic warm antibody immune hemolytic anemia, symptomatic warm antibody immune hemolytic anemia), cold antibody type (idiopathic chronic cold agglutinin disease, paroxysmal cold hemoglobinuria, symptomatic cold agglutinin disease).
(2) Alloimmune: Hemolytic disease of the newborn, ABO blood group incompatible hemolytic transfusion reaction, Rh blood group incompatible hemolytic transfusion reaction.
(3) Drug-induced immune hemolytic anemia: Can be caused by aminosalicylic acid, isoniazid, rifampin, quinidine, phenacetin, aminopyrine, sulfonamides, chlorpromazine, chlorpropamide, insulin, penicillin, cephalosporins, etc.
2. Non-immunological
(1) Mechanical factors (red blood cell fragmentation syndrome): Microangiopathic hemolytic anemia and hemolytic anemia after artificial heart valve replacement.
(2) Infectious hemolytic anemia: Malaria, sepsis, etc.
(3) Hemolytic anemia caused by biological factors: Snake venom, poisonous mushrooms, etc.
(4) Drug and chemical-induced hemolytic anemia.
(5) Hypersplenism.
(6) Disseminated intravascular coagulation (DIC)
(7) Ionizing radiation.