Anemia and clinical case
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Anemia and clinical case
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[post_date] => 2024-12-23 18:32:00
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[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Anemia is a condition in which the number of red blood cells or the level of blood hemoglobin is reduced from an individual's baseline. The clinical findings in an anemic patient are associated with decreased or insufficient oxygen delivery to the tissues, known as hypoxia. Because the causes of anemia are diverse, clinicians use multiple laboratory tests to evaluate the underlying etiology:
A patient’s hematocrit describes the proportion of whole blood that is made up of red blood cells. This can help identify whether a case of anemia is caused by a decrease in the number of red blood cells or a decrease in functional hemoglobin levels. Both hematocrit and hemoglobin concentration are volume dependent and therefore can be artificially increased or decreased depending on the patient’s volume status
The reticulocyte count is a measure of the concentration of immature RBC precursors in circulation. If anemia is due to the decreased production of red blood cells – rather than the increased destruction or loss of red blood cells – the reticulocyte count will be below the normal range.
The mean corpuscular volume (MCV) describes the average volume of circulating RBCs. Anemia with a low MCV, referred to as microcytic anemia, usually results from decreased hemoglobin levels. Anemia with a normal MCV, or normocytic anemia, may be due to a condition known as aplastic anemia, in which the stem cell precursors to all blood components (RBCs, leukocytes, and platelets) are damaged. This results in a global decrease in the number of these cells, even though they appear normal.
A patient in the ER has dry, cracked lips and symptoms of severe anemia. His blood test results are shown in Table 1.
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[question] => In what context might an anemic patient’s hematocrit and hemoglobin concentration both appear to be normal or elevated?
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[description] => Reason for Correct Answer:
Hemoglobin concentration is expressed in units of X/volume (e.g. g/dL), and hematocrit is defined as the proportion (or percentage) of whole blood taken up by red blood cells.
Because both of these levels are measured relative to volume, they are both dependent on volume.
Increased blood plasma (increased blood volume) would yield lower values for these measures. That is, increasing the denominator of the measures with a constant numerator would cause a decrease in the overall value.
On the other hand, during dehydration, plasma volume would decrease, thus the hematocrit and hemoglobin concentration could appear artificially high. That is, they appear high because the blood volume is decreased, not because there are more red blood cells or hemoglobin.
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[each_answer] => A. Dehydration
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[each_answer] => B. Increased blood plasma
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[each_answer] => C. Iron deficiency
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[each_answer] => D. Aplastic anemia
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[quiz_unique_key] => 1403770772
[question] => The production of red blood cells and white blood cells begins in what organ(s)?
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[answer] => 3
[description] => Reason for Correct Answer:
The thymus is a lymphoid organ responsible for the maturation of T lymphocytes, specifically in children.
The bone marrow is the primary site of hematopoiesis. Several other peripheral organs can be involved in hematopoiesis, such as the spleen, but to a lesser extent than the bone marrow.
White blood cells are of “lymphoid origin,” and mature in lymph organs. However, the precursors to these cells begin in the bone marrow.
Both red and white blood cell production begin in the bone marrow.
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[each_answer] => A. Red blood cell production begins in the bone marrow and white blood cell production begins in the thymus.
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[each_answer] => B. Red blood cell production begins in the thymus and white blood cell production begins in the bone marrow.
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[each_answer] => C. Both red and white blood cell production begins in the bone marrow.
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[each_answer] => D. Both red and white blood cell production begins in the thymus.
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[question] => Why would easy or abnormal bruising be a common finding in patients with aplastic anemia?
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[answer] => 2
[description] => Reason for Correct Answer:
According to the passage, aplastic anemia results from dysfunction of the stem cells responsible for producing all cells resulting from hematopoiesis.
The number of erythrocytes, leukocytes, and platelets would all decrease due to an issue of decreased production.
Increased bleeding from what would normally be recognized as inconsequential trauma most likely indicates a reduced ability of the body to repair damage to the small blood vessels (e.g. decreased hemostasis, coagulation, and clotting).
This reduced ability could be attributed to decreased platelet production in aplastic anemia, because platelets are the blood cells involved in clotting.
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[answers] => Array
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[each_answer] => A. Increased destruction of red blood cells
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[each_answer] => B. Decreased platelet production
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[each_answer] => C. Decreased red blood cell production
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[each_answer] => D. Decreased spleen function
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[question] => If present, what is a likely cause of the described patient’s anemia?
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[answer] => 1
[description] => Reason for Correct Answer:
Looking over the patient’s labs, you may notice that the hemoglobin concentration and hematocrit are low but not very far from the normal ranges. This may or may not reflect his true oxygen-carrying capacity – as the passage said, these values are dependent on volume; in addition, they do not help explain the underlying etiology of the anemia.
The patient has a high reticulocyte count. According to the passage: “The reticulocyte count is a measure of the concentration of immature RBC precursors in circulation.”
The passage states that the reticulocyte count indicates whether the patient’s anemia is due to decreased production of red blood cells or increased loss of them: “If anemia is due to decreased production of red blood cells – rather than increased destruction or loss of red blood cells – the reticulocyte count will be below the normal range.”
This patient’s high reticulocyte count indicates that there is destruction or loss of red blood cells and the body is attempting to replace them with new cells. The only answer choice that fits with increased destruction/loss of RBCs is hemolytic anemia causing the destruction of red blood cells.
Reason for Incorrect Answer:
B. Decreased red blood cell production would lead to a low reticulocyte count
C. Decreased red blood cell production would lead to a low reticulocyte count.
D. A deficiency would likely lead to low production of reticulocytes. In addition, the MCV results of this patient show that his red blood cells are small, not large.
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[each_answer] => A. Hemolytic anemia causing destruction of red blood cells
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[each_answer] => B. Damaged bone marrow induced by cancer treatment
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[each_answer] => C. Iron deficiency resulting in decreased red blood cell production
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[each_answer] => D. A vitamin deficiency resulting in larger but less mature red blood cells
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[quiz_unique_key] => 1403770772
[question] => In sickle cell anemia, a mutation occurring in the 6th codon of the gene encoding the hemoglobin subunit β (β-globin) replaces a glutamic acid with a valine residue, disrupting the tertiary structure and oxygen binding ability of the hemoglobin molecule. This mutation is damaging because it replaces an acidic amino acid with a(n):
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[answer] => 4
[description] => Reason for Correct Answer:
Here is a chart of the amino acids:
https://commons.wikimedia.org/wiki/File:Proteinogenic_Amino_Acid_Table.png
As you can see, glutamic acid (Glu) is a an acidic amino acid.
In this mutation, it is converted into valine (Val), a hydrophobic amino acid.
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[answers] => Array
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[each_answer] => A. basic amino acid.
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[each_answer] => B. polar, uncharged amino acid.
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[each_answer] => C. acidic amino acid.
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[each_answer] => D. hydrophobic amino acid.
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[quiz_unique_key] => 1997864699
[question] => The data best supports which conclusion?
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[answer] => 1
[description] => Reason for Correct Answer:
It is hard to conclude from this data that vitamin B12 deficiency was the sole cause of the patient’s anemia, as the patient’s blood values did not improve following vitamin B12 treatment and prior to iron treatment.
Hemoglobin concentrations are shown in the dots near the top of the graph. The graph shows that they started to improve right after IV iron therapy was started.
The MCV shows the size of the red blood cells. The graph shows that the MCV decreased rapidly around the start of vitamin B12 treatment, and it leveled off after vitamin B12 was started. This suggests that the treatment may or may not have caused the decrease in MCV (there was no increase).
The graph does show that after iron was started, the CHr increased. This suggests that iron increases the oxygen-carrying capacity of reticulocytes (reticulocyte hemoglobin content, or CHr).
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[each_answer] => A. Iron therapy following vitamin b12 therapy increased the oxygen-carrying capacity of new red blood cells.
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[each_answer] => B. The size of red blood cells increased as a result of vitamin B12 treatment but was normalized by iron therapy.
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[each_answer] => C. Hemoglobin concentrations increased ten days after iron therapy was initiated.
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[each_answer] => D. Vitamin B12 deficiency was the sole cause of this patient’s anemia.
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