Preliminary Review Doc: Red Blood Cell Disorders and Anemias

Comprehensive vocabulary flashcards covering the classification, mechanisms, laboratory evaluation, and microscopic morphological findings of anemias, hemolytic states, and red blood cell disorders.

Anemia

A reduction in red cell mass associated with decreased red blood cell count, hemoglobin, and/or hematocrit, resulting in impaired tissue oxygenation.

Acute blood loss

Rapid hemorrhage where a loss exceeding approximately $1,000\text{--}1,500\,\text{mL}$, or more than $20\%$, can induce shock.

Chronic blood loss

Ongoing blood loss that exceeds RBC regeneration, eventually depleting iron stores and producing iron deficiency anemia.

Intravascular hemolysis

The destruction of red blood cells directly inside blood vessels, exemplified by incompatible blood transfusion and mechanical trauma.

Extravascular hemolysis

The destruction and removal of red blood cells by macrophages, predominantly in the spleen and liver, as seen in hereditary spherocytosis, autoimmune hemolysis, and sickle cell disease.

Hereditary spherocytosis

An intrinsic RBC disorder caused by spectrin or other structural membrane abnormalities that make RBCs spherical and less deformable, leading to their entrapment and destruction in splenic sinusoids.

Sickle cell anemia

An intrinsic RBC disorder caused by a substitution of valine for glutamic acid at position 6 of the beta-globin chain, forming hemoglobin S, which polymerizes under low oxygen tension into rigid sickle-shaped cells that cause hemolysis and microvascular occlusion.

Thalassemia

An intrinsic RBC disorder marked by reduced synthesis of alpha- or beta-globin chains, leading to deficient hemoglobin production, ineffective erythropoiesis, microcytic hypochromic RBCs, and extravascular hemolysis.

G6PD deficiency

An intrinsic RBC defect causing reduced protection against oxidative injury, in which oxidized hemoglobin denatures and precipitates against the cell membrane, forming bite cells susceptible to splenic destruction following exposure to certain drugs, toxins, or infections.

Hemolytic disease of the newborn

An extrinsic RBC disorder occurring when maternal IgG antibodies cross the placenta and target inherited paternal RBC antigens on fetal red blood cells, causing extravascular hemolysis (commonly due to Rh or ABO incompatibility).

Hemolytic transfusion reaction

An extrinsic RBC disorder in which recipient antibodies react against incompatible transfused red blood cells, producing intravascular hemolysis in acute reactions and extravascular hemolysis in delayed reactions.

Autoimmune hemolytic anemia

An extrinsic hemolytic disorder characterized by autoantibodies binding to red blood cells, resulting in spherocyte formation and a positive direct Coombs test.

Mechanical trauma (RBC injury)

Extrinsic physical damage to RBCs caused by abnormal cardiac valves or fibrin strands in disseminated intravascular coagulation (DIC), leading to fragmented RBCs known as schistocytes.

Iron deficiency anemia

A microcytic, hypochromic anemia resulting from inadequate intake, increased physiological requirements, or blood loss, characterized by low ferritin, decreased serum iron, and increased iron-binding capacity.

Megaloblastic anemia

A macrocytic anemia caused by vitamin B12 or folate deficiency, where impaired thymidine synthesis delays nuclear maturation and cell division while cytoplasmic maturation continues normally, resulting in increased MCV, hypersegmented neutrophils, and marked intramedullary cell death.

Pernicious anemia

A form of megaloblastic anemia caused by autoantibodies directed against gastric parietal cells and intrinsic factor, leading to impaired vitamin B12 absorption, hematologic abnormalities, and neurologic symptoms.

Aplastic anemia

A bone marrow disorder caused by an acquired stem cell defect (often involving T-lymphocyte suppression) that reduces production of all blood cell types, causing pancytopenia and markedly decreased bone marrow cellularity.

Myelophthisic anemia

An anemia caused by the replacement of normal bone marrow space by tumor or fibrosis, characteristically leading to teardrop-shaped RBCs and frequently decreased platelets.

Relative polycythemia

An elevation in red cell concentration resulting from a reduction in plasma volume, as seen in clinical states of dehydration or severe diarrhea.

Primary absolute polycythemia

An increase in total red cell mass resulting directly from neoplastic RBC proliferation, such as in polycythemia vera.

Secondary absolute polycythemia

An increase in total red cell mass resulting from elevated erythropoietin production driven by hypoxia (cyanotic heart disease, pulmonary disease, high altitude) or erythropoietin-secreting tumors.

Mean corpuscular volume (MCV)

A red blood cell index indicating the average volume (size) of circulating RBCs, with an adult reference range of $80\text{--}100\,\text{fL}$.

Mean corpuscular hemoglobin concentration (MCHC)

A red blood cell index reflecting the average concentration of hemoglobin within circulating RBCs, with an adult reference range of $32\text{--}36\,\text{g/dL}$.

Reticulocyte count

A laboratory measure of immature red blood cells (normal adult reference range: approximately $0.5\text{--}2.5\%$ of RBCs) that increases in hemolytic anemia as the marrow compensates, but remains absent or inadequate in production defects like iron deficiency and megaloblastic anemia.

Direct Coombs test

A laboratory diagnostic test used to detect autoantibodies bound directly to RBC surfaces, testing positive in autoimmune hemolytic anemia.

Spherocytes

Small, sphere-shaped red blood cells lacking central pallor, classically seen in hereditary spherocytosis and autoimmune hemolytic anemia.

Sickled cells

Crescent- or sickle-shaped rigid RBCs that develop in sickle cell anemia when hemoglobin S polymerizes under conditions of low oxygen tension.

Target cells and basophilic stippling

Peripheral blood smear morphological findings characteristically associated with hemoglobin synthesis impairment in thalassemia.

Bite cells

Red blood cells appearing with distinct margin excavations ('bites'), characteristic of G6PD deficiency following oxidative damage and splenic removal of Heinz bodies.

Schistocytes

Fragmented red blood cells caused by mechanical shearing against abnormal heart valves or fibrin mesh networks, as seen in microangiopathic hemolytic anemias (DIC, TTP, HUS).

Teardrop cells

Teardrop-shaped red blood cells seen on peripheral blood smears in myelophthisic anemia as a result of marrow infiltration by tumor or fibrosis.