Red Blood Cell Distribution Width CV and SD

Red blood cell distribution width is a way for scientists to measure red blood cell volume and size. When red blood cells are larger than normal, that could indicate a problem. The reference range for RDW is as follows:

  • RDW-SD: 29-46 fL
  • RDW-CV: 11.6 – 14.6% (for adults)

Please keep in mind that the numbers might have a different acceptable range for children or those who have serious medical conditions.


The RDW-SD is an actual measure of size. It is derived by finding the width in fluid Liters at the 20% height of the distribution histogram. See the diagram below for a clearer visual explanation of how the number is determined. The RDW-CV is determined by taking the standard deviation of RDW-SD and the mean corpuscular volume (MCV) number. Again, see below for a visual explanation of how this works.


Indication of RDW Result

There are many things your red blood cells can tell your doctor about your health. Here are just a few of the important points about red blood cell distribution width:

  • In most cases, the RDW can help determine several points about your health, from your chances of developing an iron deficiency to different types of anemia that you may be suffering from.
  • The RDW is most helpful in alerting your doctor to the fact that there is a problem, which will then prompt him or her to call for further tests that will provide more detailed results.

1. Normal RDW and Low MCV

If you have this on your lab work, it could indicate anemia caused by a chronic disease, heterozygous thalassemia, or hemoglobin E trait.

2. Elevated RDW and Low MCV

Sickle cell anemia and iron deficiencies can be indicated by this combination of factors. In order to determine more clearly what the problem is, more detailed testing will have to be done.

3. Normal RDW and High MCV

This can be a bit more serious, depending upon the condition: You might have aplastic anemia or chronic liver disease. The use of antivirals, alcohol or chemotherapy can also prompt this result in your blood work.

4. Elevated RDW and High MCV

If both numbers are high, you might be looking at a wide variety of potential problems, including immune hemolytic anemia, myelodysplastic syndrome, or a significant folate or vitamin B12 deficiency. Chronic liver disease can also cause this, as can cytoxic chemotherapy.

5. Normal RDW and Normal MCV

Just because the numbers are “normal” doesn’t mean that all is well. On the contrary, a normal number for both of these can indicate anemia of chronic disease, anemia of renal disease, acute blood loss or hemolysis.

6. Elevated RDW and Normal MCV

These numbers can be associated with a wide variety of conditions. These include sickle cell disease, chronic liver disease or myelodysplastic syndrome. Other problems might include early stages of folate, vitamin B12 or iron deficiency. It might also mean you have dimorphic anemia, which is a marked iron or folate deficiency, just to name a few of the problems that can cause dimorphic anemia.

These blood cell counts are usually part of a normal, routine blood work that your doctor might use to determine your general overall health and possibly pinpoint any issues that might be causing adverse symptoms. Keep in mind that no matter what the RDW indicates, further tests are always necessary to help determine exactly what is wrong and how it should be treated.

Now you know all about RDW-CV and RDW-SD as well as other info in bloodwork.