Reticulocytes

Hey, this is our third video in our series on hematology. The first one, we talked about hematopoiesis. The second one, we started talking about the RBCs. But now, what is a reticulocyte?

So, as we said before, the multipotent stem cell will give a myeloid stem cell or myeloid precursor, which will give us the proerythroblast arm, all the way to reticulocyte and erythrocytes. So, before the erythrocyte or RBCs, there are reticulocytes. They are baby red blood cells. Okay, that's the topic of today. But first, let's get some terminology here. What does the reticulocyte even mean? Reticular means network—network like this. Network. Cyte means cell. Reticulocyte: a reticular cell, a network or a net-like cell. It has ribosomal RNA, which gives a bluish cytoplasm appearance. Normal level of reticulocytes is 1 to 2 percent, or we can say less than 3% is considered normal. They are reported as a percentage, not a number.

So here is the story: bone marrow will produce some reticulocyte, baby RBCs. They will go in the bloodstream. Okay, they are now created, by the way. They go to this plane thanks to splenic macrophage. They mature here into red blood cells. This whole process takes about 24 hours, or one day. And of course, you know that RBCs are non-nucleated; they are circular, biconcave; they are non-nucleated. To see the reticulocytes in the lab, we use special stains to stain them. Every single day, one to two percent of the RBC count will get replaced by reticulocytes, which are baby RBCs. And they are nucleated, and they are bluish in color.

Imagine for a moment that you're a CEO of a company that produces cell phones, and the supply is very short. Like that—customers are crying, "We don't have enough phones! We need more! We need more! We need more!" So you start to produce more phones and hire more workers. You are in a hurry, in a rush: "Let's produce more and more and MORE!" That's the case for the bone marrow in cases of anemia, or shortage of RBCs. The bone marrow will respond by increasing the production of all of the cell line of the red blood cell, including reticulocytes: produce more, more, MORE! And this reticulocyte eventually will mature to RBCs: more, more, and more. So in cases of anemia, a good bone marrow will increase production of reticulocytes. This is called a good bone marrow response, also called effective erythropoiesis. Thank you, bone marrow.

We have said before that the normal reticulocyte count is less than 3%. In anemia, what will happen? Bone marrow increases production of reticulocyte count. However, reticulocyte count will be artificially elevated. So, for example, let's say that this is the whole volume of RBCs, and you have a reticulocyte count—this is 2 percent of the whole RBCs. However, in anemia, you have less RBC mass, so this will be 9%, because it's a relative number. Okay, but this is not true; we have to correct it. We get this ridiculously high production index, aka corrected reticulocyte count. We get the hematocrit of this patient with anemia—let's say the hematocrit is 15—and we divide it by the normal hematocrit value, which is 45, so we get 1/3. Okay, we have to multiply 1/3 times reticulocyte count, which here is 9. Oops, I mean one-third times nine equals three percent. Okay, so this three percent is called the corrected reticulocyte count.

So let's say it again: increased reticulocyte count is not the same as effective erythropoiesis. We have to correct the numbers. First step, as we said, we correct the reticulocyte count, called corrected reticulocyte count. For anemia, we do what? Hematocrit, and here is the 45, okay, times reticulocyte count, okay, to get that corrected reticulocyte count. Second step: additional correction if you have polychromasia. What's polychromasia? Polychromatic RBCs are immature RBCs. They are even before the reticulocytes; they are baby reticulocytes. So they will be converted to reticulocyte then RBCs. So polychromatic RBCs, to get to mature RBCs, they do not take just one day; they take about two to three days. Okay, so these are not actual reticulocytes; however, they have the same bluish cytoplasm—here RNA—as the reticulocyte count. That's why they are mistaken for reticulocyte count. So if we are trying to count reticulocyte count, okay, mistakenly we will count the polychromatic RBCs. Well, that's not fair. Let's do additional correction for polychromasia. How we do that? We get this number, the CRC, okay, divided by two to get the final number.

Let's take an example. Let's say that there is a patient with a hematocrit of 15. Okay, we get 15 over 45, which is 1/3, times the reticulocyte count. Let's say the reticulocyte count is 18. Okay, so one-third of 18 is 6% reticulocyte count. Let's say we have polychromasia, then the CRC, which is 6%, divided by two equals three percent. Okay, three percent is considered kind of okay. This is considered, yeah, maybe effective erythropoiesis. But if we have less than three percent, like this, that's a problem; that means ineffective erythropoiesis. So let's say the three percent is four percent—that's effective erythropoiesis; the bone marrow is doing its job. However, the CRC divided by two number is one percent—that's not effective; the bone marrow is lazy; there is a problem in the bone marrow. And this will be crucial when we further discuss hematology. But for now, you got the idea, I think. That now you are confident about what a reticulocyte is. See you next video to continue our series in hematology. Please consider subscribing to get new videos as they come.