Among the components of the blood, the red blood cell (RBC) has the sole function of transporting oxygen to different body parts. Healthy red blood cells are about the same size. Suppose the red blood cells are of vastly different sizes from each other. In that case, it may be a sign of anemia, a condition characterized by not having enough healthy RBC to supply oxygen to the organs.
Anything outside the normal range in RBC width or volume indicates a possible problem in bodily function related to oxygen distribution to various body parts. A healthcare provider may use the data obtained from a red cell distribution width (RDW) test to diagnose anemia and other conditions.
What is the RDW Test?
RDW test measures the variation in red blood cell size or volume as part of a more extensive blood test called a complete blood count. It is also performed along with other RBC indices to help doctors diagnose various conditions related to RBC problems.
Contrary to popular belief, the red cell distribution width test does not measure the width of the RBS. Instead, it measures the variation in cell size among a representative sample of the RBC. Cell distribution width refers to the distance between cell sizes as they are plotted on a histogram, a particular graph type showing a range of numbers or values.
In presenting the result of the RDW test, similar values will be clustered close together in the histogram. Such values indicate a low RDW, meaning the sample has more or less the same cell size. Meanwhile, different values are spread out on the histogram, indicating high RDW. This can be interpreted as having blood samples with varied cell sizes.
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What Level of RDW is Dangerous?
Normal red blood cells maintain a standard size ranging from 6.2 to 8.2 micrometers in diameter. If the range of sizes is large, a person's RDW is elevated. This means that if your red blood cells are small on average but have tiny cells, your RDW will be elevated. Similarly, if your red blood cells are large on average but have many very large cells, your RDW will also be elevated.
For this reason, RDW is not used as an isolated parameter in interpreting a complete blood count result. Rather, it provides information about the hemoglobin and mean corpuscular value. High RDW values may indicate a person has anemia, nutrient deficiency, or other underlying medical conditions.
The normal range for red cell distribution width is 12.2 to 16.1% in adult females and 11.8 to 14.5% in adult males. If your score is outside this range, you might have an infection, a nutrient deficiency, or other disorder.
However, a person might still have a medical condition even at normal RDW levels. To receive the proper diagnosis for the condition, the healthcare provider must look at other blood tests to combine the results and provide an accurate recommendation for treatment.
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