RDW High

blood-75301_640Whenever you’ve taken your blood test, you’ve left with this list of all the abbreviations for blood cells parameters. The Complete Blood Count (CBC) has many short names for all the significant things that matter. They include parameters for red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. There are numerous different names and one of them is RDW meaning “red cell distribution width”. It is a parameter which tells us about the size variations of the red blood cells. Their normal size goes from 6-8 μm in diameter. This parameter measures the size difference which is called anisocytosis. It is expected to be around 11.6-14.6% in adults. It may vary depending on the laboratory official reference range and also the age of the patient.

What Does RDW Range Mean?

As we mentioned above, it is a parameter which tells us about the volume of the red blood cell or erythrocytes. Every blood sample has a different variation range which can be expressed in two ways. Depending on the instrument used to measure the number, the range can be presented like RDW-CV which stands for “coefficient of variation” and RDW-SD which means “standard deviation”. This can be statistically important.

RDW-SD measures the width of erythrocytes in “fL” or femtolitre. It uses 20% height level of the histogram and reports the sizing in this sample. This parameter does not get influenced by the average erythrocyte volume or mean corpuscular volume (MCV).

RDW-CV is a parameter which is expressed in percentage. It uses standard deviation method and MCV, therefore, it depends on MCV value.

RDW-CV (%) = 1 standard deviation of RBC volume/MCV x 100%

What Can RDW Range Indicate?

It is most likely to have higher RDW range than low. This can happen due to many causes and it is important to compare it with other parameters to have the right guidance and discover the root of the problem.

High RDW Accompanied With High MCV

When the both parameters are high, it can mean that the both substances fail at body detoxication. The main organ which plays a big role in system detoxication is liver. A liver takes out all the harmful substances and eliminates it. Other conditions may be anemia. It can be megaloblastic anemia due to B-12 deficiency or even hemolytic anemia which happens when the lining of the red blood cell has some structure disorders which result in fragile cell walls and early destruction of an erythrocyte. Other conditions which may lead to high RDW and high MCV are cytotoxic chemotherapy, myelodysplastic syndrome, folate deficiency and others.

Increased RDW With Low MCV

A common reason which can lead to size variation in blood and low red blood cells volume is iron deficiency. It can cause sideropenic anemia and result in a blood sample with low MCV and high RDW. When there is not enough iron in the blood, the hemoglobin building process is being disrupted which leads to lack of the function of the blood. It results in decreased ability of oxygen transportation. There are also other blood diseases such as thalassemia intermedia. It is a hemoglobin disorder which lacks β chain in a hemoglobin structure. It is the intermedia group with more mild symptoms from the opposite severe signs in thalassemia major. This will result in small red blood cells with high size variation range.

High RDW With Normal MCV

Sometimes, the blood sample results can indicate that the RDW levels are high, even when the MCV levels are normal. This can be an early sign of an iron deficiency anemia where the volume of the cells didn’t change quite that much, but there is still variation in size which results in high RDW. There are also some other conditions like B-12 deficiency which can result in high RDW with normal MCV, where the levels of the vitamin didn’t drop that low to cause the volume to shrink. The results can be such in other diseases like sickle cell disease, chronic liver disease, myelodysplastic syndrome.

When To See A Doctor

A blood test is usually ordered by the doctor with a suspicion for other problem or in order to investigate the reason of illness. You can consult with your doctor for therapy if the high results end up with certain condition diagnosis. It may need some drugs prescription and monitoring of the condition.


  1. My labs came back with high results for MCV was 101.5 & RDW 15.1. Should my doctor be doing some more testing of any sort. This wasn’t even discussed with me. I happen to look at my results later and the the two areas flagged by lab. What should I do?

    • Dear Maritza, your lab results for MCV and RDW are close to a normal range, depending on a lab that was testing. Your doctor probably wasn’t concerned about it when he saw the rest of your anamnesis, and the results you got. You can ask your doctor at your next scheduled appointment, but you shouldn’t be worried about it.

    • It looks like a fellow reader just responded to your question. If you have any other questions, please feel free to leave another comment. Thanks!

    • Dear Shelley, RDW-SD levels go from 29-46 fL, but they can differ from lab to lab, depending on their reference range. It is probably nothing, but since it depends on many medical conditions, maybe it is best to consult your doctor just to be sure.