RDW Blood Test: High, Low, What does it Mean

Our blood is an essential part of our lives. Without it circulating our system, we wouldn’t be functioning like we do today. It is important because it is composed of living cells maintaining and supporting our body tissues. Like for example, the red blood cells, in which are filled with hemoglobin, carry oxygen to our lungs and our entire bodies. The white blood cells defend us against infections, and our platelets, for instance, help blood to clot when we injure ourselves. But what if there are inconsistencies in it? How do we know? There is a process for it. This is called, “Red blood cell distribution width” or RDW Blood test.

Red blood cell distribution width or RDW Blood test measures the inconsistencies found in the blood. There are laboratory counting processes to find out the size inconsistencies of the red blood cells circulating in our body. This is also known as erythrocytes. It also estimates the hemoglobin and normally describes the complete blood count (CBC)’s factor in terms of differential diagnosis of anemia.

What is RDW on Blood Test and Normal Range?

In order to know your RDW Blood test’s status is by taking the test. The RDW Test is a way for scientists to measure our RBCs size and volume. This is how it’s done:

RDW-SD (29-46 fL) is the actual size measure. It is derived from the width in fluid Liters at 20% height. On the other hand, RDW-CV (11.6 – 14.6%) is determined when you take the standard deviation of RDW-SD and the corpuscular volume’s number. RDW denotes the parameter obtained from numerical counting of red blood cells in blood tests. It indicates the size, volume or variation of erythrocytes present in the sample. In order to have this tested, a variety of medical devices are used to conduct hematological analyses. Coefficient of variation (CV) or RDW-CV and standard deviation (SD) or RDW-SD should be calculated.

To calculate the cell distribution width of the RBS is by using a histogram. The fundamental measure of the red blood cells’ width and size are denoted by electronic instruments capable of analyzing blood samples. It detects the pulses that are produced by RBC. The stronger the pulses are, the greater the RBCs are in size. Likewise, the weaker the former is, the smaller the RBC are in size.

The aforementioned measurement basically suggests that the calculation revolves around the percentage’s elevation plane. The typical size of the red blood cells, therefore, does not provide consequences of this limit. The normal range/level of blood flow should be at 10.2% to 14.5%. Take note that it’s important to know that these ranges would be different depending on the machine used upon blood testing.

Tip: Always use the normal range found on your printed lab report upon deciding your range.

What does RDW Mean in Blood Test?

As mentioned previously, RDW denotes the parameter obtained from numerical counting of red blood cells in blood tests, thus, indicating the size, volume or variation of erythrocytes present in the sample. It estimates the hemoglobin and describes the complete blood count (CBC)’s factors in terms of differential diagnosis of anemia. This test is often done in conjunction by measuring the MCV (or mean corpuscular volume) of the RBCs. It’s the average amount of space that takes up each cell within the bloodstream.

Here’s the classification of anemias using MCV and RDW:

  1. Low RDW (low variability)

This indicates that the anemia, Thalassemia minor is both at low MCV (microcytic).

  1. Normal RDW

Thalassemia minor ranges until normal RDW (with low MCV as well). When you have normal RDW but low MCV, it is also possible that Anemia of chronic disease is present. If both are normal, Hereditary spherocytosis is present and if the MCV is high with normal RDW, the type of anemia one possess are Aplastic anemia and/or Myelodysplastic syndrome.

  1. High RDW (high variability)

If RDW is high with low MCV, it is iron deficiency. If one possesses normal MCV with high RDW, Early deficiency of iron, B12 or folate and Sickle cell anemia is the type of anemia present. If both are high, it’s B12 or folate deficiency and/or Hemolytic anemia.

Knowing the comparison between RDW and MCV measurements determines the type of anemia in blood tests. If you have a high RDW blood test result, this indicates anemia due to two things. Either a) iron deficiency, or; b) folate and vitamin B12 deficiency. Sometimes, it may also suggest hemorrhage. False calculations or readings sometimes occur, though. This happens when the wrong blood type is used on the test. Per other accounts, they suggest that high RDW results may also be because of liver diseases or hemolytic anemia.

For example: when anemia is present in a person’s blood sample and RDW and MCV are both high, then it means the person lacks folate and Vitamin B12. Per Health Research Funding, RBCs increase in size due to B12 and folate deficiency, allowing the MCV to raise. But if it’s vice versa (RDW levels are high but MCV aren’t), it is more likely the iron-deficiency type of anemia. This happens when there’s a lack of iron in the blood, causing the decrease of hemoglobin. Hemoglobin is the substance that carry oxygen through RBCs.

Indication of RDW Result

These blood cell counts determine your overall health. This is also to know and pinpoint what might cause adverse symptoms. Know that whatever is indicated in your test results, further examinations are and would always be necessary to help determine what’s wrong. This, in the event such symptoms manifest in your body. This is to also know how it should be treated thereafter.

If you have a Normal RDW but Low MCV, this indicates that your anemia is caused by a chronic disease. To assume of this circumstance based from your lab tests, conducting RWD should take place. Because this could even mean having heterozygous thalassemia or hemoglobin E trait. If the numbers are Elevated RDW and Low MCV, you probably must have the sickle cell kind of anemia and/or iron deficiencies. To further know more about this result, a variety of testing must require.

If, for instance, the numbers consist of Normal RDW and High MCV, the case can be a little serious. There is a huge possibility that chemotherapy, antivirals or alcohol shall take place. This could prompt if aplastic anemia or chronic liver disease is the result of the blood test conducted.

Elevated RDW and High MCV indicates potential problems. This could be viewed at a wide variety of dilemmas that include immune hemolytic anemia, myelodysplastic syndrome and folate or vitamin B12 deficiency. It can also cause cytoxic chemotherapy, alongside chronic liver diseases.

If you get a result of Normal RDW and Normal MCV, this means you have anemia of chronic disease, renal disease, acute blood loss or hemolysis. Just because the numbers are normal, doesn’t mean it indicates a good result. It’s still better to get (regularly) checked once symptoms arise.

While the aforementioned breakdown can reveal several things your RBC has to tell your doctor about your health, the numbers of Elevated RDW and Normal MCV doesn’t exempt itself from potential problems. This means that if these numbers appear in your results, you might want to second guess your habitual lifestyle. Why? Because this can be associated in a bunch of anemia types like sickle cell disease, chronic liver disease or myelodysplastic syndrome, early stages of folate, vitamin B12 or iron deficiency, dimorphic anemia, which is a marked iron or folate deficiency and/or dimorphic anemia. It’s better to know it firsthand from your doctor before it’s too late.


The Red Blood Cell Distribution Width testing or RDW testing can tell your doctor more about your health via your blood and its RBCs. Take note that in most cases, RDW help determine several of points and factors that could affect the chances of developing iron deficiencies. It could even pinpoint different type of anemias you may be suffering from.

RDW is also most helpful in alerting your doctor if there’s a serious or major blood problem. This will prompt him or her to conduct eventual tests that’ll provide more details about your condition. Plus, knowing the results beforehand could actually save you from major blood problems (blood cancer or leukemia, for example). Knowing your RDW result can reduce the chance being at risk.