hema midterms 2 (anemias)

Definition of anemia

A reduction in red blood cell (RBC) mass, usually reflected by a decreased hemoglobin concentration and/or hematocrit.

Three major pathophysiologic mechanisms of anemia

1. Decreased RBC production
2. Increased RBC destruction (hemolysis)
3. Acute or chronic blood loss

Key laboratory parameter for distinguishing decreased RBC production from increased RBC destruction

The reticulocyte response (reticulocyte count).

Expected reticulocyte count when bone marrow appropriately responds to anemia

An increased reticulocyte count.

Clinical significance of a low reticulocyte count in an anemic patient

Indicates an inadequate bone marrow response or impaired RBC production.

Clinical significance of an elevated reticulocyte count in an anemic patient

Indicates active marrow compensation in response to RBC destruction (hemolysis) or blood loss.

Definition of MCV (Mean Corpuscular Volume)

The average volume of an individual red blood cell.

Normal adult reference range for MCV

$$80 - 100\,\text{fL}$$

Definition of microcytosis

Red blood cells with a decreased MCV ($< 80\,\text{fL}$).

Definition of macrocytosis

Red blood cells with an increased MCV ($> 100\,\text{fL}$).

Definition of normocytosis

Red blood cells with an MCV within the standard reference interval ($80 - 100\,\text{fL}$).

Three major morphologic classifications of anemia based on MCV

1. Microcytic anemia
2. Normocytic anemia
3. Macrocytic anemia

Definition of MCH (Mean Corpuscular Hemoglobin)

The average mass of hemoglobin contained within a single red blood cell.

Definition of MCHC (Mean Corpuscular Hemoglobin Concentration)

The average concentration of hemoglobin contained within a given volume of packed red blood cells.

Definition of RDW (Red Cell Distribution Width)

A numerical measure evaluating the degree of variation in red blood cell volume.

Definition of anisocytosis

Variation in the size of red blood cells visible on a peripheral blood smear.

Clinical indication of an increased RDW

Significant variation in RBC volume, corresponding to peripheral smear anisocytosis.

Definition and characteristic feature of a reticulocyte

An immature, non-nucleated RBC that retains residual ribosomal RNA.

Primary diagnostic evaluation provided by the reticulocyte count

Evaluates the erythropoietic activity and compensatory effort of the bone marrow.

Interpretation of an increased reticulocyte count in anemia

Demonstrates an appropriate erythroid marrow response to RBC loss or destruction.

Interpretation of a decreased reticulocyte count in anemia

Demonstrates an inadequate erythroid marrow response or production failure.

Reason uncorrected reticulocyte percentage can be misleading in anemia

The relative percentage may appear falsely elevated due to a decreased total count of mature RBCs.

Calculations used to standardise reticulocyte assessment in anemia

The corrected reticulocyte count and the Reticulocyte Production Index (RPI).

Purpose of calculating the Reticulocyte Production Index (RPI)

Determines whether the bone marrow response is adequate for the severity of anemia, accounting for premature release of marrow reticulocytes.

Clinical interpretation of an RPI less than 2

Indicates an inadequate bone marrow erythroid response.

Clinical interpretation of an RPI greater than 2 to 3

Indicates an adequate compensatory bone marrow response to hemolysis or blood loss.

Two primary classification frameworks for anemia

1. Morphologic classification (based on cell size/indices)
2. Pathophysiologic classification (based on underlying mechanism)

Basis of morphologic classification of anemia

RBC size (MCV) and hemoglobin concentration (MCH/MCHC).

Basis of pathophysiologic classification of anemia

The underlying disease mechanism causing anemia (production defect, loss, or destruction).

Three major morphologic categories of anemia

Microcytic, normocytic, and macrocytic anemia.

Three core pathophysiologic mechanisms of anemia

Decreased RBC production, blood loss, and increased RBC destruction.

Definition of microcytic anemia

Anemia characterized by an MCV less than $80\,\text{fL}$.

Most common worldwide cause of microcytic anemia

Iron deficiency.

Major genetic cause of microcytic anemia

Thalassemia.

Etiologies associated with microcytic, hypochromic anemia

Iron deficiency anemia, thalassemia, anemia of chronic inflammation (late stage), sideroblastic anemia, and lead poisoning.

Effect of iron deficiency on heme and hemoglobin synthesis

Decreases heme synthesis, resulting in reduced overall hemoglobin production.

Cellular mechanism leading to microcytosis in iron deficiency

Impainred hemoglobin synthesis triggers extra cell divisions during erythroblast maturation, producing smaller RBCs.

Expected change in RDW in iron deficiency anemia

Increased RDW.

Pathophysiologic reason for elevated RDW in iron deficiency

Progressive depletion of iron creates a heterogeneous population of normal and newly formed microcytic RBCs.

Typical reticulocyte response in untreated iron deficiency anemia

Low or inappropriately normal due to lack of essential iron for erythropoiesis.

Definition of normocytic anemia

Anemia characterized by an MCV within the reference range ($80 - 100\,\text{fL}$).

True or False: Normocytic anemia can result from decreased RBC production.

True. Normocytic anemia can arise from production failures as well as acute destruction or loss.

Common etiologies of normocytic anemia

Acute blood loss, hemolytic anemia, anemia of inflammation (early), renal insufficiency, and primary bone marrow failure.

Reason early iron deficiency presents as normocytic

Microcytosis requires time to manifest as mature normocytic cells gradually age out of circulation.

Key diagnostic test to initial workup of normocytic anemia

The reticulocyte count (or RPI) to distinguish hyperproliferative from hypoproliferative states.

Definition of macrocytic anemia

Anemia characterized by an MCV exceeding $100\,\text{fL}$.

Two broad diagnostic subdivisions of macrocytic anemia

Megaloblastic macrocytic anemia and nonmegaloblastic macrocytic anemia.

Definition of megaloblastic anemia

Macrocytic anemia caused by defective DNA synthesis, resulting in characteristic megaloblastic changes in bone marrow precursor cells.

Nutritional deficiencies classically responsible for megaloblastic anemia

Vitamin $B_{12}$ (cobalamin) deficiency and Folate (vitamin $B_9$) deficiency.

Cellular defect caused by impaired DNA synthesis in erythropoiesis

Nuclear maturation is delayed relative to cytoplasmic growth, resulting in nuclear-cytoplasmic asynchrony.

Definition of nuclear-cytoplasmic asynchrony

A cell maturation abnormality where cytoplasmic development proceeds normally while nuclear chromatin maturation lags behind.

Classic peripheral blood smear features in megaloblastic anemia

Macro-ovalocytes and hypersegmented neutrophils (five or more lobes).

Common causes of nonmegaloblastic macrocytosis

Alcohol consumption, liver disease, reticulocytosis (marked), hypothyroidism, and myeldysplastic syndrome.

Definition of hemolytic anemia

Anemia resulting from premature destruction of circulating red blood cells (RBC lifespan $< 120$\,days).

Expected reticulocyte response in hemolytic anemia with an intact bone marrow

Markedly elevated reticulocyte count.

Two broad mechanistic divisions of hemolytic anemia

Intrinsic (corpuscular) defects and extrinsic (extracorpuscular) defects.

Definition of intrinsic hemolytic anemia

Hemolysis caused by an inherent structural or functional abnormality within the red blood cell itself.

Three major categories of intrinsic red blood cell defects

1. Membrane defects
2. Hemoglobinopathies
3. RBC enzyme deficiencies

Definition of extrinsic hemolytic anemia

Hemolysis driven by environmental or external factors acting upon structurally normal red blood cells.

Major causes of extrinsic hemolytic anemia

Immune destruction (autoantibodies/alloantibodies), mechanical trauma, infections, toxins, and drugs.

Examples of intrinsic RBC membrane defects causing hemolysis

Hereditary spherocytosis and hereditary elliptocytosis.

Examples of intrinsic hemoglobin disorders causing hemolysis

Sickle cell disease and hemoglobin C disease.

Examples of intrinsic RBC enzyme defects causing hemolysis

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and pyruvate kinase deficiency.

Classic example of immune-mediated extrinsic hemolytic anemia

Autoimmune hemolytic anemia (AIHA).

Example of mechanical extrinsic hemolytic anemia

Microangiopathic hemolytic anemia (MAHA).

Characteristic RBC morphologic finding in microangiopathic hemolytic anemia

Schistocytes (fragmented red blood cells).

Target detected by the Direct Antiglobulin Test (DAT)

Immunoglobulins (antibodies) and/or complement proteins bound directly to the surface of the patient's RBCs in vivo.

Diagnostic utility of the Direct Antiglobulin Test (DAT)

Differentiates immune-mediated hemolytic anemia from non-immune hemolytic etiologies.

Initial essential clinical inputs when starting an anemia evaluation

Patient clinical history, physical examination, and baseline initial laboratory findings.

Core Complete Blood Count (CBC) parameters in an anemia workup

Hemoglobin, hematocrit, RBC count, MCV, MCH, MCHC, and RDW.

Primary diagnostic role of MCV in clinical evaluation

Directs the initial morphologic classification (microcytic, normocytic, or macrocytic).

Diagnostic role of the reticulocyte count in clinical evaluation

Assesses whether bone marrow production is responding appropriately to reduced RBC mass.

Diagnostic importance of examining peripheral blood morphology

Identifies diagnostic poikilocytes, inclusions, and cellular patterns characteristic of specific diseases.

Stain used for standard peripheral blood smear review

Wright stain (or Wright-Giemsa stain).

Key RBC characteristics evaluated on a peripheral blood smear

Cell size, cell shape (poikilocytosis), color (chromasia), inclusion bodies, maturity, and distribution pattern.

First step in the diagnostic algorithm for anemia evaluation

Assess the MCV to classify the anemia as microcytic, normocytic, or macrocytic.

Diagnostic category indicated when MCV is low ($< 80\,\text{fL}$)

Microcytic anemia.

Key differential considerations for microcytic anemia

Iron deficiency anemia, thalassemia trait/disease, anemia of chronic inflammation, and sideroblastic anemia.

Diagnostic category indicated when MCV is within normal limits ($80 - 100\,\text{fL}$)

Normocytic anemia.

Immediate next laboratory parameter to evaluate in normocytic anemia

Reticulocyte count / Reticulocyte Production Index (RPI).

Differential diagnosis when MCV is normal and reticulocytes are elevated

Hemolysis or acute blood loss.

Differential diagnosis when MCV is normal and reticulocytes are low/normal

Hypoproliferative anemias (e.g., marrow insufficiency, renal failure, chronic inflammation).

Diagnostic category indicated when MCV is high ($> 100\,\text{fL}$)

Macrocytic anemia.

First diagnostic branch to consider in macrocytic anemia

Determine if the etiology is megaloblastic vs. nonmegaloblastic.