RDW Blood Test: What It Means and What It Tells About Your Health

RDW blood test: What It Means and What It Tells About Your Health

Red cell distribution width (RDW for short) is a blood test used to measure the difference in size and volume of your red blood cells. Doctors use the RDW blood test as part of a complete blood test to help diagnose certain conditions that can affect your health. A blood test to measure variations in blood cell size can help diagnose causes of anemia, heart disease, diabetes, and liver disease.

The normal range for measuring the differences in the size of red blood cells (erythrocyte) is between 11.8% and 14.6%. RDW level greater than 14.5% means that there is a large degree of variation in red blood cell size. Elevated red blood cell distribution width could mean that a person is anemic and is at risk of other health conditions.

In this article, you will learn about the RDW blood test and what it means for your health. Using results from checking RDW level can help in the early diagnosis and successful treatment of certain health issues.

What is Red Cell Distribution Width (RDW) Blood Test?

RDW lab test is usually part of a complete blood count (CBC) and is used in conjunction with the MCV test results (or, red blood cell mean corpuscular volume) to tell about your health. Usually, a doctor will take the blood test if there are concerns that you have anemia.

According to Dr. Choladda Vejabhuti Curry on Medscape, the RDW results themselves won’t confirm or rule out any type of anemia. Doctors will also take into account other indices on the complete blood test results like MCV and MCHC levels (mean corpuscular hemoglobin concentration).1

What are Low, Normal, and High RDW Levels?

According to doctors from the Mayo Clinic, the RDW reference range is 11.8% to 15.6%.2 However, some other clinics give the normal reference range for RDW between 11.6% and 14.6%. But, reference ranges may depend on the laboratory performing the test.3

The normal red blood cell distribution width in children will be slightly different. The RDW test results for children should be between 12% and 14% depending on their age.2

What RDW Blood Test Can Tell About Your Health

High and normal RDW levels in a blood test can help to tell a lot about your health. Taking RDW levels and comparing them with other red blood cell indices can allow doctors to check for anemia, vitamin B12 deficiency, low levels of iron, and other blood disorders.

According to Medscape, the RDW results from a blood test can help determine the cause of the anemia and, therefore, how to treat it. This is what RDW blood test results along with MCV results can tell about your health:4

Normal RDW and normal MCV. Normal levels of both the RDW and MCV parameters could mean that you have anemia due to chronic blood loss or because of a chronic disease.

Normal RDW and low MCV. A low mean corpuscular volume with normal RDW can indicate that anemia is caused by a chronic disease or the inherited blood disorder thalassemia.

Normal RDW and high MCV. If your RDW levels are normal but MCV is too high, then this could mean that you have liver problems or your blood has been affected by alcohol, antivirals, or chemotherapy treatment. If you have a low lymphocyte count (lymphocyte is a type of white blood cell) you may have aplastic anemia.

Elevated RDW and normal MCV. RDW blood tests that show high levels but normal MCV can mean that iron, vitamin B12, or folate levels are too low. RDW that is too high with normal MCV could also be a sign of chronic liver disease.

Elevated RDW and low MCV. High RDW levels can mean that you have an iron deficiency if your MCV readings are lower than normal.

Elevated RDW and high MCV. If both your MCV levels and RDW levels are too high, then this could be caused by vitamin B12 or folate deficiencies, anemia, or chronic liver disease.

What Low, Normal, or High RDW Levels Can Mean

Let’s look in a bit more detail at the different health conditions that doctors can diagnose from your RDW blood test results.


Very often anemia is the cause of abnormalities with your RDW results. If the distribution width of your red blood cells is too low or too high, this can indicate that you have anemia.

For example, the Journal of the Indian Medical Association reported that high RDW is associated with microcytic hypochromic anemia.5 Also, the Mymensingh Medical Journal reported that taking into account RDW and other complete red blood cell count indices can help to determine iron deficiency anemia in people who are at risk of anemia, for example, pregnant women.6

If you have an iron deficiency anemia, you may also have chest pains, pale skin, cold hands and feet, poor appetite and inflammation of your tongue. You may also have low MCH levels, and low Hematocrit levels if you suffer from iron deficiency anemia.

The best way to increase your body’s iron levels is through diet. Some great sources of iron are beef, seafood, and chicken as well as kale, cooked beans, and pumpkin or sesame seeds. You can find more information about iron deficiency in my article about top signs of iron deficiency and how to increase iron levels in your blood.

Some of these natural sources of iron can also help deal with a vitamin B12 deficiency naturally which can also cause anemia. The easiest way to prevent vitamin B12 deficiency is by consuming different meats, seafood, milk and eggs as well as nutritional yeast and vitamin B12 fortified products, such as B12 fortified almond milk and cereals, and some breads.

Heart disease

Doctors can use results from RDW blood test to see if you are at more risk of developing heart disease. Erythrocyte (red blood cell) distribution width that is above normal levels could mean that there is a greater chance of suffering a heart attack, stroke, or peripheral artery disease.

According to the Journal of Thoracic Diseases, elevated RDW is a common factor in patients who suffer from some form of cardiovascular disease. Checking RDW as part of a CBC blood test can also help indicate if a person is at risk of recurring heart problems or the chances of recovering successfully from a stroke or heart attack.7

You shouldn’t wait until you get a blood test done to know if you are at risk for a stroke or heart attack. Please read my article on the 5 easy ways to greatly reduce your risk of developing cardiovascular disease. You should also know the early warning signs of a heart attack and stroke, as they can help to save life.

High blood pressure

RDW levels can also tell a lot about your cardiovascular system and your risk of high blood pressure (hypertension). Although doctors can easily check your blood pressure using a sphygmomanometer, studies have shown that there is a link between RDW and hypertension.

The journal Experimental & Clinical Cardiology reported on the connection between RDW and high blood pressure. As well as high blood pressure putting a person at an increased risk of stroke, high RDW levels can also indicate other cardiac problems.8

One way to help reduce high blood pressure naturally is by making positive lifestyle changes. These can include eating a well-balanced diet with plenty of fruit, vegetables, and whole grains, exercising regularly, as well as taking other natural supplements mentioned in my article on how to reduce high blood pressure naturally.


Doctors may check red cell distribution width to check for diabetes. Diabetes is caused by the body not producing enough or not responding properly to insulin. Diabetes can cause spikes in blood sugar levels, increased urination, and other serious complications. You can also get familiar with these early warning signs of diabetes you shouldn’t ignore.

Researchers have also found that RDW in diabetic patients is often increased. A study from 2015 found that RDW is significantly higher in people with diabetes. The study found that this was also connected with hypertension, and that regulating hypertension helped to reduce RDW.9

Some people with diabetes are able to manage diabetes symptoms with diet. However, other diabetics need regular insulin shots and should be under regular supervision by their doctor.

Autoimmune conditions

Differences in red cell distribution width can also be connected with certain autoimmune conditions. According to the journal Clinical Hemorheology and Microcirculation, RDW is an inflammatory marker that can help to diagnose anemia and autoimmune disorders. Researchers found that people with lupus had increased RDW whether they had anemia or not.10

Liver or Kidney Disease

If your liver or kidneys are not working properly, then this can show up in an RDW blood test. Your kidneys and liver play important roles in filtering out toxins from your blood. However, if they become damaged by disease, then RDW may increase and lead to other complications.

According to Medical Consultant Dr. Clifton Titcomb, RDW and MCV blood test can help in establishing liver disease. Dr. Titcomb said that normal RDW and low, normal, or high MCV could be a marker that there are problems with your liver.11

Also, a study from Scandinavia found that blood tests from people with impaired kidney function show increased RDW and can also be associated with cardiovascular disease.12

It is important to take care of the health of your kidneys and liver. Therefore, it’s important to know the first signs of kidney disease and how to protect them. Also, reducing alcohol intake, quitting smoking, and maintaining healthy body weight are all ways to help prevent damaging your liver.


It is common for pregnant women to suffer from anemia and have increased RDW level in their blood tests. A study in the International Journal of Gynaecology and Obstetrics reported that changes in RDW happen throughout pregnancy. Doctors will address any iron and vitamin deficiencies to help keep mother and baby healthy. However, it was also found that in the few weeks before labor, RDW increase dramatically in preparation for giving birth.13

Lung disease

In some cases, elevated RDW in a blood test can help doctors treat patients with lung disease better. Dr. Clifton Titcomb says that checking CBC for red cell distribution width can be a marker to determine outcomes in people with pulmonary conditions.11

You can find more information in my article about early signs of lung disease and how to strengthen your lungs.


Some types of cancer cause a great variation in size and volume distribution of red blood cells and doctors can use this as one of the markers to diagnose some cancers. According to the journal Haematologica, RDW is higher in some people with cancer and can help determine the seriousness of the disease.12 Also, doctors can use RDW to help screen for breast cancer and determine the best course of treatment.13

However, you should remember that RDW is not in itself a determining factor in the presence of cancer. In most cases, RDW is an indicator of anemia and needs to be taken in context with other results from blood tests and diagnostic procedures.

Other Related Blood Tests

MCV blood test

MCV blood test stands for mean corpuscular volume of your blood cells and helps doctors check the health of your blood. The MCV blood test shows the average size of your red blood cells, as red blood cells that are too large or too small can be an indicator of an underlying medical condition.

You can get more information about MCV blood test in the article: MCV Blood Test: What It Means and What It Tells About Your Health.

MCHC blood test

Another way to check the health of your red blood cells is using the MCHC blood test. MCHC stands for mean corpuscular hemoglobin concentration. In other words, it measures the concentration of hemoglobin in a given volume of red blood cells.

You can get more information about MCHC blood test in the article: MCHC Blood Test: What It Means and What It Tells About Your Health.

MPV Blood Test

MPV blood test measures the mean platelet volume in your red blood cell count. The average size of your platelets can help doctors identify certain blood disorders and help diagnose underlying health conditions.

You can get more information about MCHC blood test in the article: MPV Blood Test: What It Means and What It Tells About Your Health.

Read my other related articles:


Article Sources

  1. Medscape. Red cell distribution width.
  2. MayoMedicalLaboratories. CBC with differential blood.
  3. Medscape. Red cell distribution width.
  4. Medscape. Red cell distribution width.
  5. J Indian Med Assoc.2011 May;109(5):297-9.
  6. Mymensingh Med J.2013 Apr;22(2):370-6.
  7. J Thorac Dis. 2015 Oct; 7(10): E402–E411.
  8. Exp Clin Cardiol. 2010 Fall; 15(3): 37–40.
  9. Diabetes Metab Syndr Obes. 2015; 8: 525–533.
  10. Clin Hemorheol Microcirc.2013 Jan 1;54(3):333-9.
  11. Hannover. Red cell distribution width.
  12. Scand J Clin Lab Invest.2008;68(8):745-8.
  13. Int J Gynaecol1998 Jul;62(1):43-6.

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