This lesson will discuss the major and interesting causes of normocytic anemia. Using terms such as RDW, MCV, and anemia of chronic disease you'll gain an appreciation for why normocytic anemia may occur.
Slightly Misleading Terminology
There are terms in our language that are partially correct but perhaps slightly misleading. Lead pencils are pencils, but they're actually made of graphite. Tin foil is foil but made from aluminum.
This lesson will cover something known as normocytic anemia. The name is slightly misleading. Normocytic anemia isn't normal, despite the first word, because it's still anemia no matter what, and that's a medical problem that needs to be addressed.
Anemia is a term that describes a decrease in the amount of red blood cells or hemoglobin. There are many different types, subtypes, and causes for each kind of anemia. In order for a doctor to try and get to the bottom of what may be the cause of the anemia, it helps to classify anemia by its presentation on blood work.
Therefore, a complete blood count (a CBC) is used to measure different red blood cell values. A CBC is a report about some of your body's functions. If your body was a car, a mechanic would do the same thing by inserting a scanner into the car to figure out what may be wrong with a particular system. In medicine, we insert a needle and submit the blood collected for analysis of the body.
Some diagnostic codes that pop up on a CBC are mean cell volume, or MCV, and red cell distribution width, or RDW. These are just two 'codes' that help us try to pinpoint the cause of anemia in a patient. If the MCV is in the normal range of values in an anemic patient, we term this normocytic anemia. Normocytic refers to red blood cells that are of a normal size. That is to say, they're not abnormally large or abnormally small.
Causes for Normocytic Anemia
If the MCV and RDW are both within their normal ranges, then the most likely cause of normocytic anemia is anemia of chronic disease. Anemia of chronic disease refers to anemia as a result of long-standing medical conditions, such as cancer and autoimmune diseases. There's more than one possibility as to why anemia of chronic disease occurs, but one of these has to do with inflammatory factors released during a disease process.
In virtually any disease, inflammation occurs in the body. Inflammation is characterized by the release of all sorts of factors and molecules that initiate, promote, or stop the process of inflammation. Some of these factors destroy the precursors of red blood cells in the bone marrow, thereby leading to anemia.
Think of a product assembly line in a car plant. In order to get the final product, you need to assemble the car in a series of steps. If something, like a fire (which represents inflammation in the body), destroys the car as it is being assembled, or maturing, then you never get the final product.
Another important cause of normocytic anemia is chronic kidney disease. If the kidneys are badly damaged, then they cannot secrete erythropoietin, or EPO. EPO is a hormone produced in the kidneys that tells the bone marrow to produce red blood cells. In this case, our production plant never gets the signal to begin making cars in the first place.
Also, normocytic anemia can occur due to hemolysis (the destruction of red blood cells) or a sudden hemorrhage - that is to say, blood loss occurring internally or externally. In the case of the former, our car is simply destroyed right after it leaves the plant! In the case of the latter, the car is lost or stolen and, therefore, is no longer able to provide a service, like allowing its owner to drive around town. When it comes to red blood cells, that service is carrying oxygen around the body.
Now, there's a slight variation to normocytic anemia. If in normocytic anemia the MCV is normal but RDW is increased, then a suspicion of an early case of folate, vitamin B12, or iron deficiency may be appropriate. Normally, prolonged cases of folate and vitamin B12 deficiency cause macrocytic anemia, where the red blood cells are large. Conversely, chronic cases of iron deficiency anemia, the leading cause of anemia worldwide, are microcytic. This is where red blood cells are small in size. But in the beginning, all of these may be normocytic in nature.
Other Causes for Normocytic Anemia
By no means have we covered all the possible causes of normocytic anemia. Sickle cell disease is one other possibility. And so is myelophthisis. That's one weird looking and sounding word! Myelophthisis refers to the destruction and replacement of normal hematopoietic and supportive cells by abnormal and nonhematopoietic cells. Hematopoietic cells are cells that engage in hematopoiesis, the formation of blood, which includes things like red blood cells, white blood cells, and platelets.
In so many words, myelophthisis is when the bone marrow fails because it is invaded by the wrong kinds of cells that destroy the cells that produce normal blood. The most common cause of this type of bone marrow suppression is metastatic cancer. Here, malignant cells, cells that shouldn't be there, invade the bone marrow and simply destroy the normal cellular architecture. This may result in fibrosis, or scarring, of the bone marrow. Since the bone marrow is scarred and destroyed, it leads to myelophthisic anemia because the bone marrow cannot produce any more blood cells of any kind in any significant amount.
Going back to our car factory example, it's as if the entire factory was taken over by bandits who burn down the entire place. Since the factory is destroyed, no cars can be produced of any make, model, or color, and the entire automotive industry shuts down. It's so severe that even the stuff that happened to the automotive industry in Detroit can't compare!
Again, myelophthisis, the destruction and replacement of normal hematopoietic and supportive cells by abnormal and nonhematopoietic cells, is only one form of normocytic anemia. Hematopoiesis, by the way, refers to the formation of blood.
Normocytic anemia is characterized by normocytic cells, or red blood cells that are of a normal size. Meaning, our MCV is within normal limits on the CBC.
The most common cause of normocytic anemia is anemia of chronic disease. Anemia of chronic disease refers to anemia as a result of long-standing medical conditions. It is suspected that inflammatory molecules destroy red blood cell precursors in the bone marrow, resulting in anemia.
Once you have completed this lesson, you should be able to:
- Illustrate how to diagnose anemia
- Define normocytic anemia, list its characteristics, and explain how it is diagnosed
- Recall the main causes of normocytic anemia