Determination of Coefficient of Variaiton of Red Blood Cell Distribution Width (RDW-CV) Manually
We know that the most important components of a Complete Blood Count report are, of course, the Hemoglobin, the White Cell Count and Differential, Red Cell Count and the Platelet Count. However modern hematology machines that produce the CBC results are able to calculate several other derived parameters that provide more information. These are the red cell and platelet indices – MCV, MCH, MCHC, RDW and the MPV and PDW. (We here will talk about the RDW only and the other parameters will be discussed later in another posts)
These parameters are rarely used because many physicians and doctors are less familiar with them. Our goal as science students and graduates is to make doctors learn the significance of these parameters to prove ourselves, to prove that we can study clinical medicine and work as clinical lab Specialist, especially in Egypt in which the Doctors fight science students and graduates to not work in clinical lab investigations although student sciences have more knowledge in this field than Egyptian Doctors [this is the goal of our site, to prove ourselves) (see about us section)]
1) What is the RDW?
RDW stands for Red Blood Cell Distribution Width…… when you read the word “WIDTH” you can imagine that we mean the width of the red blood cell itself but this is not true….
The RDW is the measure of the variation of the volume of Red Blood Cell (RBC)…. so, if this is its definition how the word WIDTH doesn’t mean the width of the RBC????????
actually, the modern device measure the volume of many RBCs and plot a curve – like that in the following image between the Frequency and the MCV (the frequency means the amount of RBC of the same volume) – ——- the device then measure the width of the Histogram and divide it by the mean MCV to find the RDW
So, the word WIDTH refers to the width of the hisogram
2) The Value of the RDW:
When you read a Complete Blood Count report and find that hemoglobin level is low, you say that it could be anemia>>>> but what is the type of this anemia??? is it iron deficiency or hemolytic anemia or Vitamin B12 deficiency anemia or what?…………..Of course, you can’t define the type of anemia by the Hb level alone.
Usually red blood cells are a standard size of about 6-8 μm. Certain disorders, however, cause a significant variation in cell size. Higher RDW values indicate greater variation in size. Normal reference range in human red blood cells is 11–15%.
If anemia is observed, RDW test results are often used together with mean corpuscular volume (MCV) results to determine the possible causes of the anemia. It is mainly used to differentiate an anemia of mixed causes from an anemia of a single cause for example Vitamin B12 deficiency produces a macrocytic anemia (large cell anemia) with a high RDW. However, iron deficiency anemia initially presents with a varied size distribution of red blood cells, and as such shows an increased RDW. In the case of a mixed iron and B12 deficiency, there will normally be a mix of both large cells and small cells, causing the RDW to be elevated. An elevated RDW (red blood cells of unequal sizes) is known as anisocytosis.
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