Anemia

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Temperature101

Temperature101

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Anemia is characterized by a reduced oxygen carrying capacity of the blood, most commonly due to a decrease in hemoglobin production or a reduction in red blood cell count. Would an individual who was mildly anemic due to iron deficiency experience an increase in resting ventilation rate?

A. No, anemia does not directly affect blood gas concentrations or blood pH.

B. No, in the absence of hemoglobin more oxygen would dissolve in the plasma.

C. Yes, the lack of oxygen would cause blood pH to increase.

D. Yes, the lack of oxygen would lead to an excess of carbon dioxide and a decrease in blood pH.

Answer: A
 
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It's A. Acidosis or alkalosis aren't cause by the hematocrit level of the blood.

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B and C are obviously wrong. The key to the question is "mild" anemia. A mild iron-deficiency anemia with a small decrease in hemoglobin will most likely be a asymptomatic, as hemoglobin can fall to crazy numbers in some people ( about 3) before they even start to experience symptoms. The question here is about the ventilation rate, which is obviously getting at whether or not decreased tissue oxygenation (hypoxia) as a result of decreased blood oxygen (hypoxemia) will result in a metabolic acidosis (which involves decreased HCO3 and pH) leading in increased ventilation to blow off excess CO2 to increase pH and compensate for the metabolic abnormality. I'd say in a mild anemia (heavy menstrual bleeding, nutritional deficiency, blah blah blah) the heart rate may increase when needed to provide more perfusion to the tissues, but there wouldnt be hypoxia, acidosis, and hyperventilation. The body generally has a large functional reserve for this kind of thing and the anemia would most likely become "severe" before anything interesting started to happen.
 
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freshbagels said:
It's A. Acidosis or alkalosis aren't cause by the hematocrit level of the blood.

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Right answer, poor explanation. Even if hematocrit was not directly related to pH levels, the question stem indicates that the type of anemia in question could be due to reduced Hb. Therefore, hematocrit could be normal.

Knowing why answers are correct/incorrect are just as important as getting the question right during MCAT prep.
 
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MedPR said:
Right answer, poor explanation. Even if hematocrit was not directly related to pH levels, the question stem indicates that the type of anemia in question could be due to reduced Hb. Therefore, hematocrit could be normal.

Knowing why answers are correct/incorrect are just as important as getting the question right during MCAT prep.
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Could you go through the problem in excruciating detail? 😳 I'm having trouble understanding what you're saying about the question stem. It says anemia is commonly caused by low Hb production or low RBC count. The individual in question has an iron deficiency. Nothing is said about the individual having low Hb count/production.

Temperature101, I ask because image187's answer isn't satisfying, precise, or in line with what I'd expect from the MCAT. "I'd say," "generally," "most likely," etc.
 
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circulus vitios said:
Could you go through the problem in excruciating detail? 😳 I'm having trouble understanding what you're saying about the question stem. It says anemia is commonly caused by low Hb production or low RBC count. The individual in question has an iron deficiency. Nothing is said about the individual having low Hb count/production.

Temperature101, I ask because image187's answer isn't satisfying, precise, or in line with what I'd expect from the MCAT. "I'd say," "generally," "most likely," etc.
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The poster I originally replied to gave an incorrect/irrelevant explanation for the correct answer.

They essentially said that RBC count has nothing to do with pH. While that may be true (I don't know if it is or not) it is not a good enough reason to pick answer A because the question stem says that anemia is also caused by low Hb. Low Hb doesn't mean low hematocrit.
 
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circulus vitios said:
Could you go through the problem in excruciating detail? 😳 I'm having trouble understanding what you're saying about the question stem. It says anemia is commonly caused by low Hb production or low RBC count. The individual in question has an iron deficiency. Nothing is said about the individual having low Hb count/production.

Temperature101, I ask because image187's answer isn't satisfying, precise, or in line with what I'd expect from the MCAT. "I'd say," "generally," "most likely," etc.
Click to expand...

forget about hematocrit for a moment. The question is asking whether low hemoglobin is directly related to respiratory rate. The answer is no, because while it indirectly can increase rate via tissue hypoxia in a severe situation, the direct stimulator of respiration is CO2 and H+ ions produced in a metabolic acidosis. The hemolobin does not directly effect ventilation. Does this make more sense?

As an aside, hemoglobin and hematocrit are not the same thing and can be different, however, for practical purposes the hematocrit is an artificially generated number with most labs just multiplying hb by 3. hematocrit is basically a useless number
 
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Also, I think you may have confusion with what happens in iron deciciency anemia. Just to clear things up, anemia is a general word for decreased oxygen carrying capacity of the blood, whether it's due to hemolysis from an auto immune reaction, blood loss through a wound, decreased hemoglobin production due to a deficiency or a toxin... I think you get that. in iron-deficiency anemia, body iron (which is needed for hemoglobin production) stores are insufficient to meet the demand for making hemoglobin. As a result, RBC production is abnormal and cells are fewer, smaller, and more pale. We call this a microcytic hypochromic anemia. The RBC count, hemoglobin, and hematocrit are all lower than they should be. This represents a decreased oxygen carrying capacity of the blood. This by itself will NOT directly stimulate respiration, as this has nothing to do with arterial O2 content, and everything to do with products of cellular respiration like CO2, H+. Is there still any confusion?
 
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It's hard to believe that the MCAT would want you to know the difference between mild and severe anemia unless they explicitly defined the terms in a passage. D says that lack of O2 will lead to too much CO2. This makes no sense and won't ever be true (unless the person is holding their breath). Low O2 =/= More CO2, so it's false. You could just read the list of possible answers and rule that one out, without even knowing what the question is. A is really the only answer that makes sense, just by process of elimination.

Just going through the options:

B - not true, right off the bat.
C - blood pH would rise with hyperventilation which kind of makes sense if someone has low O2 levels, but it wouldn't increase because of the low O2 levels
D - see above.

That leaves you with A. No knowledge of anemia, hematocrit, etc, required.
 
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