Classification and Laboratory Assessment of Anemias

CHAPTER 11: Classification and Laboratory Assessment of Anemias

absolute iron deficiency anemia: A type of anemia where there is a quantitative decrease in iron available in the body, resulting in inadequate hemoglobin production.
anemia: A condition characterized by a deficiency of red blood cells (RBCs) or hemoglobin, leading to reduced oxygen transport in the body.
functional iron deficiency anemia: A condition in which iron stores in the body are adequate, but the iron cannot be mobilized quickly enough to meet the increased demand for erythropoiesis.
macrocytic: Refers to red blood cells that are larger than normal, often seen in certain types of anemia.
microcytic: Refers to red blood cells that are smaller than normal, usually associated with iron deficiency or thalassemia.
normocytic: Refers to red blood cells that are of normal size, often seen in types of anemia where production and loss are in balance or dysfunctional.

Explain the relationship of anemia as it relates to normal erythrocyte kinetics.
Compare the core problem of absolute iron deficiency anemia and functional iron deficiency anemia.

Describe the organization of anemias according to erythrocyte size and explain the limitation of such a system.
Give examples of macrocytic anemias and pathological megaloblastic anemias.
List the laboratory assays that can be used to identify the various categories of anemia.
Briefly explain the characteristics of categories of anemia using a pathophysiological basis.
Compare the morphologic and pathophysiological categories of anemia.

List the supplementary assays that may be of assistance in establishing a specific anemia diagnosis.
Compare the findings of basic tests performed in the hematology laboratory to supplementary assays that assist in establishing a differential anemia diagnosis.

Definition: Anemia is considered to be present if the hemoglobin concentration of the RBCs or the packed cell volume of RBCs (hematocrit) is below the lower limit of the reference range for the individual's age, gender, and geographical location.
Functional Anemia: Defined as a decrease in the ability of RBCs to carry oxygen to tissues, resulting in a state of hypoxia.
Underlying Disorders: Anemia may signal underlying disorders, including liver disease, alcohol toxicity, hypothyroidism, and myelodysplasia, which can alter red blood cell parameters.

Anemia development relates to normal erythrocyte kinetics, balancing the production of new erythrocytes against those that reach their lifespan of about 120 days.
When the survival of erythrocytes decreases, the bone marrow must increase production to maintain a balance, known as homeostasis.
Increased erythropoiesis (as shown by elevated reticulocyte counts) depends on available iron and protein for hemoglobin synthesis.
Iron Deficiency Anemia:
- Absolute Iron Deficiency Anemia: Characterized by a true reduction in body iron stores.
- Functional Iron Deficiency Anemia: Body iron stores may be sufficient, but mobilization is insufficient to meet increased erythropoietic needs, common in chronic inflammation and disorders.

Clinical manifestations arise from decreased oxygen delivery to tissues due to low hemoglobin concentrations.
Symptoms: Common complaints include easy fatigue, dyspnea on exertion, vertigo, faintness, headache, and heart palpitations.
Physical Findings: Anemic patients often present with pallor, low blood pressure, slight fever, and edema. Specific clinical findings may be tied to specific types of anemia.

Anemia classifications can be based on etiology, yet none are entirely satisfactory due to overlap in subcategories. It is beneficial to classify based on pathology and morphology.

Anemias are categorized by red cell morphology into microcytic, normocytic, and macrocytic.
Limitations: This classification does not provide insight into the etiology of the anemia.

Associated with maturation defects; non-megaloblastic types arise from hemolytic or posthemorrhagic processes and diseases like alcoholism and liver disease.
Examples: Includes pernicious anemia, folic acid deficiency, myelodysplasia, and erythroleukemia.
Macrocytes should be evaluated for shape, hemoglobin content, central pallor, and presence of inclusions.

Hypoproliferative Anemias: Exhibit normal RBC sizes and characterized by hypocellular bone marrow with normal or increased myeloid:erythroid (M:E) ratios.
Increased Reticulocyte Counts: Seen in hemolytic anemia (intrinsic or extrinsic causes).

Occur due to defective hemoglobin synthesis, typically when iron availability is compromised.

Categories of Causes:
1. Impaired Red Cell Production: Occurs in disorders such as aplastic anemia or deficiencies of vitamin B12 and folate.
2. Accelerated Erythrocyte Destruction: Sudden turnover due to hemolysis, either inherited or acquired.
3. Blood Loss: Can be acute or chronic; overwhelmed marrow capacity for RBC replacement, often seen in iron deficiency anemia.

Assessments include both quantitative and qualitative measurements of RBCs, supplemented by various tests.
Defining Anemia: Characterized by major laboratory findings—decreased hemoglobin concentration, reduced packed cell volume, lowered erythrocyte count, and decreased mean corpuscular hemoglobin (MCH).

Testing Variables: Hemoglobin concentration and hematocrit can be influenced by plasma volume changes, hemoglobin variations, and abnormal hemoglobins.
Measurements include red blood cell indices, a red cell histogram, reticulocyte count, and bone marrow examination if needed.
Bone Marrow Examination: Indicated for inconclusive cases, revealing various abnormalities in erythropoiesis, assessing cellularity (M:E ratios), and presence of pathologies such as leukemia.

Erroneous assessments may be clarified by measuring fetal hemoglobin, performing malarial smears, assessing platelet counts, and conducting multiple specific hematological assays.

Anemia is present if hemoglobin levels are below the reference range adjusted for age, gender, and location.
Functional anemia denotes reduced RBC capacity to supply oxygen.
A solid understanding of erythrocyte kinetics is essential for recognizing the developmental aspects of anemia.