Anemia: Definition and Hemoglobin Synthesis

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Questions and Answers

What does anemia signify in terms of red blood cells?

An increase in RBCs

A normal level of oxygen delivery

A decrease in the number of RBCs or hemoglobin (correct)

An appropriate response to physical activity

At what point does hemoglobin F typically stabilize after birth?

At 4 weeks after birth

At 16 to 20 weeks after birth (correct)

At 12 months after birth

At 30 weeks’ gestation

Which type of hemoglobin is the major component found in normal adult blood?

Embryonic hemoglobin

Hemoglobin F

Hemoglobin A (correct)

Hemoglobin A2

What is the minimum hemoglobin level considered abnormal for a full-term infant?

14 g/dL Signup and view all the answers

Which globin chain is absent in the adult hemoglobin structure?

Gamma Signup and view all the answers

What constitutes the average hemoglobin value for small for gestational age preterm infants?

17.1 g/dL Signup and view all the answers

What is the characteristic of the genes for globin chains in humans?

Clustered on chromosomes 11 and 16 Signup and view all the answers

Which embryonic hemoglobins start to dominate at different stages of development?

Gower 1, Portland, Gower 2, and fetal Hb Signup and view all the answers

What is the main switch in hemoglobin synthesis that occurs in infants after birth?

Synthesis of β chains begins Signup and view all the answers

Which factor is NOT considered in the clinical features of anemia?

Dietary habits Signup and view all the answers

Which type of anemia is characterized as microcytic hypochromic anemia?

Iron deficiency anemia Signup and view all the answers

What type of anemia usually arises from an abnormal bone marrow?

Impaired erythrocyte production Signup and view all the answers

Which is considered anemia for adult females?

Below 11.5 g/dl Signup and view all the answers

Which of the following is a specific sign associated with iron deficiency anemia?

Spoon-shaped nails Signup and view all the answers

What is the result of increased 2,3-DPG concentration in the O2 dissociation curve?

Shift to the right Signup and view all the answers

What is the normal range for reticulocyte count?

50-150 X 10^9/L Signup and view all the answers

Which inherited condition is associated with membrane defects leading to hemolytic anemia?

Hereditary spherocytosis Signup and view all the answers

Which condition is NOT typically associated with microcytic anemia?

Vitamin B12 deficiency Signup and view all the answers

What is the major classification of anemia based on morphology?

Macrocytic, Microcytic, Normocytic Signup and view all the answers

What characterizes macrocytic anemias regarding MCV and RBC size?

MCV greater than 100 fL with large RBCs Signup and view all the answers

Which method is NOT a part of the laboratory diagnosis of anemia?

Skin biopsy Signup and view all the answers

Which laboratory finding helps to distinguish pure anemia from pancytopenia?

Reticulocyte count Signup and view all the answers

What can an increased reticulocyte count during anemia suggest?

Increased erythropoietin level Signup and view all the answers

What is the most common cause of microcytic anemia?

Iron deficiency Signup and view all the answers

What does megaloblastic anemia primarily present with in peripheral blood?

Oval macrocytes and hypersegmented neutrophils Signup and view all the answers

Which characteristic feature distinguishes nonmegaloblastic macrocytic anemias from megaloblastic anemias?

Membrane changes due to lipid ratio disruption Signup and view all the answers

What range of mean corpuscular volume (MCV) is typical for normocytic anemias?

80 to 100 fL Signup and view all the answers

Which of the following conditions can lead to an elevated reticulocyte count?

Hemolytic anemias resulting from premature RBC destruction Signup and view all the answers

How can a dimorphic population of RBCs in a normocytic anemia be verified?

By observing a bimodal distribution on the RBC histogram Signup and view all the answers

In which condition is it rare for the MCV to exceed 115 fL?

Nonmegaloblastic macrocytic anemias Signup and view all the answers

Which of the following best describes the origin of extrinsic hemolytic anemias?

Immune and nonimmune RBC injury Signup and view all the answers

What is a typical characteristic found in the erythroid precursors of megaloblastic anemias?

Large nucleated erythroid precursors Signup and view all the answers

Study Notes

Definition of Anemia

Anemia is a decrease in the number of red blood cells (RBCs) or the amount of hemoglobin in the RBCs, resulting in reduced oxygen delivery and tissue hypoxia.
It's a manifestation of underlying disease processes, not a disease itself.

Hemoglobin Synthesis

Hemoglobin synthesis involves an orderly progression of embryonic, fetal, and adult hemoglobins.
Hb F (fetal hemoglobin) comprises 60-90% of total hemoglobin at birth, decreasing to around 3.2% by 16-20 weeks post-birth.
The switch from Hb F to Hb A (adult hemoglobin) is genetically controlled based on gestational age.
Normal adult blood contains Hb A (α2β2), Hb F (γ chains), and Hb A2 (δ chains).

Hemoglobin Abnormalities

Result from abnormal hemoglobin synthesis or reduced synthesis of normal α or β globin chains (α and β thalassemia).

Clinical Features of Anemia

Considered based on speed of onset, severity, age, and oxygen dissociation curve.
Rapid progressive anemia causes more symptoms than slow-onset anemia.
Mild anemia may be asymptomatic.
Older patients tolerate anemia less than younger individuals.
Pyruvate kinase deficiency shifts the oxygen dissociation curve to the right.

Symptoms and Signs

Shortness of breath, weakness, palpitations, and headache are common symptoms.
Pallor of mucous membranes is a general sign.
Less frequent signs include tachycardia, cardiomegaly, and cardiovascular impairment.
Specific signs are associated with different types of anemia (e.g., spoon nails with iron deficiency, jaundice with hemolytic anemia, leg ulcers with sickle cell anemia).

General Classification of Anemia

Based on Morphology:
- Macrocytic anemia (MCV > 100 fL)
- Microcytic hypochromic anemia (MCV < 80 fL)
- Normocytic normochromic anemia (MCV 80-100 fL)
Based on Etiology:
- Impaired erythrocyte production
  - Abnormal bone marrow (e.g., aplastic anemia)
  - Essential factor deficiency (iron, vitamin B12, folic acid)
  - Stimulation factor deficiency (e.g., anemia of chronic disease)
- Accelerated erythrocyte destruction (hemolytic anemia)
  - Intracorpuscular defect (intrinsic RBC factor)
    - Membrane defect (e.g., hereditary spherocytosis)
    - Enzyme deficiency (e.g., G6PD deficiency)
    - Hemoglobin abnormalities (e.g., thalassemia)
  - Extracorpuscular defect (nonintrinsic RBC factor)
    - Mechanical (e.g., MAHA)
    - Chemical or infectious causes
- Excess blood loss (e.g., accident, GI bleeding)

General Aspects of Anemia

Anemia is defined as hemoglobin concentration below normal levels.
Adult male: < 13.5 g/dL
Adult female: < 11.5 g/dL
Newborn infant: < 14 g/dL
Anemia usually, but not always, involves reduction in red blood cell count and PCV level.

Laboratory Diagnosis

Complete Blood Count (CBC)
Reticulocyte count and Reticulocyte Production Index (RPI)
Peripheral blood examination
Bone marrow examination
Other laboratory tests:
- Iron studies
- Urinalysis
- Stool analysis
- Liver and renal function tests
- Serum vitamin B12 and folate assays

Other Laboratory Findings

Leukocytes and Platelets Count: Helps distinguish anemia from pancytopenia (reduction in all blood cells), suggesting general marrow defects like hypoplasia.
Reticulocyte Count: Normal level is 50-150 x 10^9/L (0.5-2.5%). Increased in anemia due to increased erythropoietin level. A lack of increase in reticulocyte count with anemia may indicate impaired marrow function or erythropoietin synthesis defect.

Morphologic Classification of Anemias and Reticulocyte Count

Microcytic Anemias:
- MCV < 80 fL, RBCs < 6 μm.
- Often associated with hypochromia (increased central pallor in RBCs) and MCHC < 32 g/dL.
- Caused by reduced hemoglobin synthesis, heme synthesis (iron deficiency, chronic inflammation, sideroblastic anemia, lead poisoning), or globin chain synthesis (thalassemia, Hb E disease).
- Iron deficiency is the most common cause, manifesting early as reduced iron stores without microcytosis or anemia.
Macrocytic Anemias:
- MCV > 100 fL, RBCs > 8 μm.
- Result from megaloblastic or nonmegaloblastic red cell development in the bone marrow.
- Megaloblastic anemias are due to impaired DNA synthesis (vitamin B12 and folate deficiency, myelodysplasia), leading to asynchrony between nuclear and cytoplasmic development, resulting in larger cells.
- Characterized by oval macrocytes, hypersegmented neutrophils, and megaloblasts in bone marrow.
- Nonmegaloblastic macrocytic anemias are characterized by large, round RBCs, often seen with liver disease, alcohol abuse, and bone marrow failure.
Normocytic Anemias:
- MCV 80-100 fL.
- Need peripheral blood film examination to rule out dimorphic populations (microcytes and macrocytes) which can yield a normal MCV.
- Can develop from hemolytic anemias (premature destruction of RBCs), characterized by elevated reticulocyte count, and further divided into intrinsic (membrane defects, hemoglobinopathies, enzyme deficiencies) and extrinsic (immune and nonimmune RBC injury) causes.

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Description

This quiz covers the definition of anemia, its clinical features, and the process of hemoglobin synthesis. It discusses the types of hemoglobin present at different stages of life and the impact of abnormalities in hemoglobin synthesis. Test your knowledge on these crucial topics in hematology.