5.1 Anemia

Nov 08, 2026 14:10 · 7:00 · English · Whisper Turbo · 1 Àwọn Àkọ́lé

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Welcome to Chapter 5,

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Red Blood Cell Disorders.

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The vast majority of this chapter actually deals with anemias.

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We're going to subdivide the anemias and talk about them in groups.

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However, before we actually begin,

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it's important to gain a general understanding of anemia.

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Anemia is defined as a reduction in circulating red

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blood cell mass.

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This is the technical definition of anemia.

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And we're well aware of the fact that red blood cells carry the vast majority

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of oxygen within the blood.

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In particular,

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the hemoglobin within the red blood cell carries the vast majority of oxygen

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within the blood.

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And therefore,

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if patients have a reduction in red blood cell mass,

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they're gonna present with signs and symptoms of hypoxia.

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Some of those signs would include weakness,

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fatigue,

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and dyspnea.

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Dyspnea being shortness of breath.

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Pale conjunctiva in skin,

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and this is a relatively good clinical test.

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Pale conjunctiva is a good sign that there is an anemia.

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The patient may present with headache and lightheadedness due to hypoxia to

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the central nervous system,

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in particular the brain.

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And the patient may even exhibit signs and symptoms of angina.

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Angina is chest pain.

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And because there's low oxygen in the blood,

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there would be low oxygen delivery to the heart.

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And if the patient has some pre -existing situation that has

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already decreased the blood flow to the heart,

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for example coronary artery disease,

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then a further decrease in oxygen in the little bit

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of blood that's actually going to the heart could actually result in signs and symptoms of

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angina.

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These are the classic signs and symptoms of hypoxia.

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Now,

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once we have a patient with signs and symptoms of hypoxia,

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then the next discussion becomes how we can prove that

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they actually have an anemia.

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And remember that the technical definition of an anemia is a

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decrease in red blood cell mass.

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Unfortunately,

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it's very difficult to measure the red blood cell mass.

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Obviously, we can't take a patient and bleed them and then measure...

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how much their red blood cells weigh.

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So it's very difficult to measure.

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There are ways to do it,

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but it would be very expensive and very difficult.

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So instead of measuring red blood cell mass,

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we use some surrogate markers.

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And these surrogate markers help us to determine or make an effort to

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determine exactly what the patient's red blood cell mass might be.

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The three key laboratory studies that are used are hemoglobin,

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hematocrit,

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and the red blood cell count.

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So these three markers,

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hemoglobin,

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hematocrit, and the red blood cell count,

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are used as surrogates for red blood cell mass.

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Now you could actually stop me and say,

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well, you know, why are these surrogates?

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Why don't we just say that they equal the red blood cell mass?

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And the answer is that each of these is concentration dependent.

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And so they could,

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in some...

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circumstances not be a good estimate of red blood cell mass.

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For example,

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a woman may have normal red blood cell mass when she's pregnant,

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however, because her blood volume increases so much,

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her hemoglobin and hematocrit actually go down.

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And because the hemoglobin and hematocrit go down,

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that doesn't mean that she's got a decrease in red blood cell mass,

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it just simply means that she's got more blood volume,

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and so she's diluted out her normal red blood cell mass.

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So that might be one circumstance in which a patient could

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have a lower hemoglobin or hematocrit but would still have a normal red blood cell mass.

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Another example,

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just to again highlight this principle,

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let's say a patient gets a gunshot wound.

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if they get a gunshot wound,

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they're obviously going to bleed out both red blood cells and fluid.

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And so immediately after the gunshot wound,

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when there's blood loss,

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the patient's hemoglobin and hematocrit would be normal.

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What's going to show you that there was actually blood loss is that

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when you give the patient fluid or when the patient eventually gets fluid

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back into their system,

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that's gonna dilute down the remaining red blood cells,

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and then that will result in a decrease in the hemoglobin and hematocrit.

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And so, again,

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another reason why these are just surrogates.

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But for our discussions and for the purposes of what we want to consider,

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I think that the hemoglobin in hematocrit and the red blood cell

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count are relatively useful for

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determining red blood cell mass.

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The technical definition of anemia is a hemoglobin less

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than 3 .5 grams in males and a hemoglobin or a

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hemoglobin less than 12 .5 grams in females.

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We accept a lower hemoglobin in females because females

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normally lose a little bit of blood during their menstrual cycle,

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and therefore their hemoglobin may be slightly lower

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in the normal female.

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When you think about anemias,

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there's a lot of ways to divide anemias.

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And I think this,

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for me,

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at least as a student,

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had made anemia a particularly difficult subject.

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For example,

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you can look at some textbooks,

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and some textbooks will say,

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divide anemias based on underproduction or overdestruction.

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And that would be one way to look at anemias.

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Another textbook might look at anemias and say,

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Well, let's divide anemia as based on problems with the red blood cell and

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problems with something other than the red blood cell,

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so extrinsic or intrinsic defects.

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That's another way to look at anemia.

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However,

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my personal feeling is that the best way for a student...

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who's learning about anemia,

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to understand anemia,

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is to divide it based on the MCV.

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The MCV is the mean corpuscular volume,

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and it tells you basically,

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it gives you an estimate of the size of the red blood cell.

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And for me,

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if you understand anemia based on the size

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of the red blood cell,

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that makes it very easy to learn the

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different anemias.

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And you'll see why as I take you through the remainder of this lecture.

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I'm fairly confident that once you learn anemias the way that I'm going to explain

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it to you, you'll actually be very comfortable with anemias,

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you'll be very comfortable with them clinically,

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you'll be very comfortable with them for examination purposes.

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And of course,

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anemias are something that we regularly and routinely see,

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both clinically as well as on any type of examination.

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Let's just remind ourselves that the normal red blood cell has an MCV,

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or a mean corpuscular volume,

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of about 80 to 100.

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That's the normal.

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80 to 100 would be normal.

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Less than 80 is considered microcytic,

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i .e.

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the cells are smaller than they normally should be,

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and greater than 100 is considered macrocytic,

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i .e.

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the cells are bigger than they normally should be.

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And so we're going to divide anemia into three types.

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Microcytic anemias,

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macrocytic anemias,

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and normocytic anemias.

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And so these are the next three sections that you're going to cover

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and we'll do them obviously,

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we'll take them one at a time and do them sequentially.

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So let's stop there,

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that's the basic introduction and the next section's going to deal with microcytic anemias.

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