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Questions and Answers
What happens to glutamic acid in the mutation associated with Hgb SS?
Which test is used to detect the presence of Heinz bodies in red blood cells?
What characteristic is associated with unstable hemoglobins during the heat denaturation test?
Which of the following is classified as Hgb disease characterized by only one beta chain mutation?
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What is one of the conditions that can trigger sickling of red blood cells?
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Which hemoglobin variant is associated with hereditary persistence of fetal hemoglobin?
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Which test is used to screen for sickle cell anemia?
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What happens to red blood cells when they become sickle-shaped?
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What is the consequence of sickle cells being trapped in microvascular channels?
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Which substances are involved in the sodium metabisulfite test for sickle cell detection?
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Which genetic disorder is characterized by having only one sickle cell gene?
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What role does sodium dithionite play in the sickle cell diagnostic testing?
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What effect does dehydration have on the hemoglobin molecule in sickle cell anemia?
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Which of the following conditions is most likely to occur when there is an incompatibility between maternal and fetal blood?
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What is the primary purpose of performing intrauterine transfusion in blood banking?
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Which hemoglobin variant is confirmed during the screening process mentioned?
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Which of the following hemoglobin types would most likely precipitate when sodium metabisulfite is added?
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In the sodium dithionite solubility test, which factor can lead to a false negative result?
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What type of environment is characterized by a pH of 8.0 in hemoglobin electrophoresis?
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What does the presence of turbidity in the sample indicate during testing?
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Which hemoglobin types migrate toward the positive charge in standard electrophoresis?
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What type of defect is characterized by an imbalance in the number of globin chains?
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Which of the following tests is used for screening unstable hemoglobin?
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What is the typical observable result of an unstable hemoglobin when subjected to an alcohol solution?
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In which position of the beta globin chain does sickle cell anemia occur?
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Which of the following is NOT a characteristic of qualitative hemoglobin disorders?
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What indicates the presence of a problem in red blood cells during Heinz bodies testing?
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Which of the following conditions is related to enzyme deficiencies leading to Heinz bodies?
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What happens to a specimen subject to incubation that shows turbidity?
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What can be concluded if heavy precipitation occurs when testing for unstable hemoglobin?
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What typically happens to normal hemoglobin when subjected to a precipitation test?
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Study Notes
Sickle Cell Anemia
-
Background:
- Caused by a point mutation in the beta globin chain of hemoglobin.
- The mutation causes the amino acid glutamic acid to be replaced by valine at the sixth position of the beta globin chain.
- Hemoglobin with this mutation is called Hemoglobin S (Hgb S).
- Changes the shape of red blood cells from normal to sickle-shaped.
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Triggers for Sickling:
- Low oxygen tension
- Dehydration - lack of fluid in the body increases crystallization of Hgb S.
- Low blood pH (acidosis)
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Testing for Sickle Cell:
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Sodium Metabisulfite Test (Sodium Dithionite Solubility Test)
- Principle: Sodium metabisulfite causes oxidation and precipitation of Hgb S, leading to the formation of tactoids (sickle-shaped structures).
- Procedure:
- A blood smear is treated with sodium metabisulfite.
- Observe for turbidity (cloudiness) in the sample, indicating the presence of Hgb S.
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Appearances:
- Holly-leaf: Most likely indicative of Hgb AS (sickle cell trait).
- Sickle: More likely to be Hgb SS (sickle cell anemia).
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Cellulose Acetate pH 8.0 Electrophoresis:
- Alkaline environment - Standard order of migration towards the positive charge should be Hgb A, F, S, C.
- Abnormal migration: Faster migration of Hgb S towards the positive charge indicates a possible presence of Hgb S (either SS or AS).
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Sodium Metabisulfite Test (Sodium Dithionite Solubility Test)
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Complications of Sickle Cell Anemia:
- Vaso-occlusive crisis: Sickle cells block blood flow in the spleen, kidney, or other organs, leading to pain and tissue damage.
- Hemolytic anemia: Macrophages remove sickle cells from the blood, leading to anemia.
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Clinically Significant Hemoglobin Variants:
- SS: Sickle cell anemia
- AS: Sickle cell trait
- SC
- SD-Punjab
- SO-Arab
- S-B thalassemia
- SE
- S-heredity persistence fetal Hgb
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Unstable Hemoglobin:
- Caused by amino acid substitution resulting in instability of the Hgb molecules, affecting the normal shape of the RBC.
- Can be tested using:
- Heat denaturation test
- Isopropanol precipitation test
- Heinz bodies test
- Clinical Significance: Unstable hemoglobin can cause hemolytic anemia and other complications.
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Hemolytic Disease of the Newborn (HDN):
- Also known as erythroblastosis fetalis.
- Occurs when the mother's blood is incompatible with the fetus's blood.
- Intrauterine transfusion: Performed in the blood banking section to transfuse blood to the fetus inside the mother's womb.
Unstable Hemoglobin
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Qualitative defects:
- Involve problems with the structure of the Hb molecule.
- Examples include sickle cell anemia.
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Quantitative defects:
- Involve problems with the amount of globin produced or their ratio.
- Example: Thalassemia (imbalance in the number of globin chains)
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Screening Tests:
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Heat Denaturation Test:
- Unstable Hb precipitates heavily when incubated at 50°C for an hour.
- Normal Hb shows small precipitate.
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Isopropanol Precipitation Test:
- Nonpolar solvents weaken bonds of Hb, causing precipitation.
- Normal Hb takes 40 minutes to precipitate.
- Unstable Hb precipitates much faster, within 20 minutes.
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Heinz bodies test:
- Heinz bodies are visible in red blood cells under a microscope.
- Indicate problems with the cells, often related to enzyme deficiencies, such as G6PD Deficiency.
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Heat Denaturation Test:
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Laboratory Tests:
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Isopropanol Precipitation Test:
- Uses 17% alcohol solution and measures precipitation time.
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Heat Denaturation Test:
- Incubation at 50°C for one hour.
- The turbidity of the sample is examined, indicating the presence of unstable Hb.
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Heinz Body Test:
- Uses acetyl phenylhydrazine to detect the presence of Heinz bodies in red blood cells.
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Isopropanol Precipitation Test:
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Importance of Screening:
- Identify individuals with unstable hemoglobin that may require special care, such as monitoring and treatment to prevent hemolytic crises and complications.
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Description
Explore the intricacies of sickle cell anemia, including its genetic basis stemming from a point mutation in hemoglobin. Learn about the triggers for sickling and the testing methods used to diagnose this condition. This quiz will enhance your understanding of this significant hematological disorder.
