Transcription
So, we continue our talk about hematology. If you haven't already watched the previous videos, please go ahead and watch them. I'll link the playlist in the description. Today's topic is red cell distribution width, or RDW. What's that? You will know whenever we are trying to diagnose an AMI, and the lab, we need RDW. Why? Because it's important. What's RDW, or red cell distribution width? It measures the variation of RBC diameter. Okay, so let's say we have a small RBC and a medium one and big and bigger. There is a variation. When there is a size variation, we call it anisocytosis. Let's break that down. Anisocytosis. What's the name? What's the meaning of "an"? No, it's a Greek word. "An" – ISO means the same; cyto means cell; osis means condition. It's the condition of cells of different sizes. Okay. Red cell distribution width measures the variation in the diameter. Okay, so when cells are of different diameters, the RDW is high. There is an increase in the distribution of widths, you see. So, the normal RBC diameter equals around 7 micrometers. The normal RDW is a percentage of the variation and normally between 11.5 and 14.5%. It's only significant as elevated. So, if we measure the RDW and it's in the normal range, it's insignificant; it doesn't tell me anything. But if it's elevated, that's crucial; that's of importance. So, when the RBCs are the same size, the RDW is normal. When they are of different sizes—i.e., the variation is big—that's increased RDW. What's the name of the condition? Anisocytosis.
So, to understand why cells vary in size, especially in anemia, we have to discuss it. Okay, so this is the bone marrow, and the bone marrow is producing cells that are normal size or normal diameter—i.e., normocytic RBCs. Okay, that's fine. Let's say now that I am deficient in iron. I am not getting enough iron, and there is iron deficiency, which will cause iron deficiency anemia. But it will happen gradually. So, first, bone marrow still has kind of enough iron, so it will produce normal cells. Then, the iron will decrease. Okay, so cells will get smaller because I don't have enough iron. I'm making RBCs big enough, kind of, to make my iron equal for the production, so it's okay. Then they're getting smaller and smaller and smaller and smaller, from normocytic to microcytic. Okay, it happens gradually. Okay, so the RDW will catch the difference between this one and this one, and we will have elevated RDW. Rome did not fall in a day, neither did the bone marrow; it happens gradually. So, an iron deficiency anemia, as we'll discuss in a separate video, there we have microcytic anemia with increased RDW, as we've said before. In vitamin B12 deficiency, we will have macrocytic anemia again with increased RDW. So, please remember this. However, let's see thalassemia. It's a genetic disease. Okay, there is no deficiency, so there is no gradual deterioration of the bone marrow production. Okay, so the RDW is normal. I'm already having the problem from the beginning; nothing is decreasing; I'm not getting deficient gradually. It's genetic; RDW is normal.
So, let's summarize the whole idea behind RDW: RDW is elevated in nutritional anemia but normal in genetic anemia. Genetic causes of anemia—thalassemia—will have normal RDW. Nutritional anemias, such as iron deficiency and B12 deficiency, will have increased RDW. Remember, iron deficiency anemia almost always has an increased RDW. Thank you very much. Please subscribe, and see you next video.