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What can high or low levels of RDW indicate in a blood test

RDW is an acronym for Red Cell Distribution Width, which evaluates the variation in size between the red blood cells, that are called anisocytosis.

Therefore, when the value is high in your blood count, it means that the red blood cells are larger than normal, and very large and very small red blood cells can be seen on the blood smear. When the value is below the reference range, it usually has no clinical significance, only if, in addition to the RDW, other indexes are also below the normal range, such as VCM.

The RDW is one of the parameters that make up the blood count and, along with the other information provided by the test, it is possible to verify how the blood cells are produced and your general state of health. When the result of the RDW is altered, it is possible to be suspicious of some situations, such as anemia, diabetes or liver problems, whose diagnosis must be made from the analysis of the complete blood count and biochemical tests. See how to interpret the results of a complete blood count.

What can high or low levels of RDW indicate in a blood test

What is the reference range

The reference value for RDW in the blood count is 11 to 14%, however, this result may vary according to the laboratory. Therefore, if the range is above or below that percentage, it may have different meanings and so it is always important that the value is evaluated by your doctor who requested the test.

High RDW level results

Anisocitosis is the term that occurs when the RDW is increased, being able to be seen in the blood smear a great variation of size between red blood cells. RDW may be increased in some situations, such as:

  • Iron deficiency anemia;
  • Megaloblastic anemia;
  • Thalassemia;
  • Diseases of the liver.

In addition, people undergoing chemotherapy or are taking some antiviral drugs may also have increased RDW levels.

Low RDW level results

Low RDW usually does not present clinical significance when interpreted alone, however if other changes in the blood count are noted, it may indicate anemia caused by chronic disease, such as liver disease, kidney problems, HIV, cancer or diabetes, for example.

When can the test be requested

This test is often called for when anemia is suspected because symptoms such as dizziness, tiredness or pale skin appear, for example. See what are the main symptoms of anemia.

However, the doctor can also ask for this test when you have or had:

  • Family history of blood changes;
  • Bleeding during surgery or after a blow;
  • Diagnosis of a disease that can cause changes in blood cells;
  • Chronic disease, such as HIV.

Sometimes this test can even be ordered on a routine blood test, without a specific cause.

How to prepare for the test

In order to perform a complete blood count and, consequently, the RDW, it is not necessary to perform fasting. However, the blood count is usually requested along with other blood tests that require a fasting of at least 8 hours.

Usually blood collection takes less than 5 minutes and is easily in the hospital or at any testing clinic with the removal of a small sample of blood from the vein.

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