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Red Blood Cells: Important Measurements

Red Blood Cells: Important Measurements
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  • 0:01 Measured in Many Ways
  • 0:42 Red Blood Cells and Hematocrit
  • 3:40 The Reticulocyte
  • 5:41 MCV, MCH, MCHC
  • 8:51 Red Cell Distribution Width
  • 9:32 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will discuss many red blood cell related values found on a complete blood count, including RBC, Reticulocytes, Hct, PCV, MCV, MCH, MCHC, and RDW, as well as their importance.

Measured in Many Ways

When you step into a doctor's office, you are measured in many ways. Your height, weight and blood pressure are all taken in order to appreciate important changes since you were there last, how they may be impacting your health and how much of a medication you should receive.

These types of measurements are performed on you, the whole person. But we also employ these types of measurements to one little cell in your body: the red blood cell. We'll go over a bunch of the ways we measure red blood cells in a blood test called a complete blood count and some of the things these measurements tell us about what's going on inside of you.

Red Blood Cells and Hematocrit

After your blood is drawn and analyzed, test results come back to indicate several different things. The first and most obvious is called the red blood cell count. It's exactly what it sounds like. The red blood cell count, or RBC, tells a doctor if you have normal amounts of red blood cells, too many or too few in your body.

A normal amount is roughly 4 - 6 million cells per microliter and varies a bit for men and women. The exact number isn't what I want you to worry about though. What I want you to understand is why you may have too many or too few RBCs.

Too many RBCs, termed erythrocytosis, can occur as a result of normal processes, such as high altitude elevations. If you climb mountains, then you know there's less and less oxygen as you climb higher and higher. But your body needs oxygen to live. Because your tissues are starved for oxygen, your body produces more red blood cells in hopes of catching more oxygen high in the sky. Another cause for increased RBCs isn't normal and is called polycythemia vera, which is a blood disorder that causes overproduction of red blood cells. These are just two examples.

Conversely, a decrease in RBCs is technically termed anemia. It can occur as a result of many different types of anemia, such as hemolytic anemia, a process where red blood cells are destroyed due to any number of reasons ranging from infection to drugs to autoimmune disease. Additionally, hemorrhage, that is to say bleeding in excessive amounts, can cause a decrease in RBCs, simply because, let's face it, if you're bleeding out then you're bleeding out a lot of red blood cells. If this loss exceeds production capacity, the number of red blood cells will decrease, as well.

Furthermore, chronic renal (kidney) failure can cause decreases in RBCs because the kidneys are very important in producing a hormone called erythropoietin or EPO. This hormone stimulates red blood cell production. If the kidneys are really sick, they can't make EPO, and the bone marrow isn't stimulated to produce RBCs. You've probably heard of EPO if you've followed the Tour de France or Lance Armstrong. Its synthetic forms are something that's used in blood doping to improve performance by increasing the number of oxygen-carrying red blood cells in an athlete.

Besides a RBC count, a CBC (a complete blood count test) will also have something known as hematocrit, or Hct, for short. Hematocrit is the percentage of the volume of blood that is made up of erythrocytes (red blood cells). Practically speaking, Hct is synonymous with packed cell volume, which is abbreviated as PCV.

The causes for increases and decrease of hematocrit are basically the same as those for RBCs. Hct is also oftentimes increased when a person is dehydrated.

Reticulocyte Count

Now, I just told you that erythrocytes are red blood cells. Well, cute looking baby red blood cells are called reticulocytes. They are also an important component in figuring out if, during anemia, your bone marrow is regenerating enough RBCs or not. That is to say, if your body is able to respond to the loss of red blood cells by making more of them in enough quantity and quality or not.

If elevated levels of reticulocytes, reticulocytosis, is noted, then we can assume the bone marrow is able to respond to the loss of red blood cells by making lots of babies. In this case, the body is so distressed about the fact that it's lost so many red blood cells, it kicks out baby red blood cells before they mature due to the serious demand for red blood cells in circulation. Reticulocytosis usually occurs when there is the hemolytic anemia or hemorrhage.

If, however, the reticulocyte count is low, then we must assume the bone marrow is unable to produce enough red blood cells. If there isn't enough EPO to signal the bone marrow to produce RBCs, if the bone marrow is barren because it is destroyed due to cancer, or if chronic nutrient deficiency, such as iron deficiency occurs, then low numbers of reticulocytes are noted since the bone marrow doesn't have the signal or resources to produce enough red blood cells or hemoglobin.

Because the reticulocyte count alone can sometimes be misleading in cases of anemia, a corrected reticulocyte count is calculated, but I don't want you to worry about that for now. Just understand the basic pathophysiology I described before.

As an interesting point, if a patient of yours comes with a sudden and severe onset of blood loss, due to something like hemorrhage, then bear in mind that just like it takes time to produce a human baby, it takes time to produce reticulocytes, about 2 - 3 days. Therefore, this patient will not have reticulocytosis noted on blood work right away.

MCV, MCH, MCHC

Because the red blood cells are so important in your body, there are many more ways by which we measure them.

One of these is known as mean corpuscular (cell) volume, or MCV. It's basically exactly what it sounds like; it's a measurement of the volume of an erythrocyte, or red blood cell, that decreases or increases in relative proportion to the size of the red blood cell itself. I don't think that's too difficult to understand. If you have a really big sized balloon, the volume of air that can fit within it will be much higher than in a small balloon.

Therefore, we classify the size of the red blood cells based on MCV into three groupings.

  • Normocytic: a normal red blood cell size, if the MCV is normal
  • Microcytic: an abnormally small red blood cell, if the MCV is low
  • Macrocytic: an abnormally large red blood cell, if the MCV is high

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