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High RDW level in the blood

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High RDW level in the blood
Last update: 12/01/2021

What is a low RDW called?

  • Anisocytosis

What is the normal RDW level in the blood?

If you need to know which are the RDW reference ranges or you require more information about the role of RDW in the blood you can visit: Normal RDW level in the blood

What does a low RDW in a blood test mean?

A high RDW is called anisocytosis, a condition when the red blood cells are unequal in size. The RDW is essentially an indication of the degree of anisocytosis (abnormal variation in size of RBCs).

A high RDW percentage is useful in the existence of anemia (hemoglobin low) and it should be studied within the MCV (Mean Corpuscular Volume) to discern the different types of anemia:

  • If MCV is high and RDW is also high it may be due to:
    • Megaloblastic anemia
    • Autoimmune hemolytic anemia
  • If MCV is low whereas RDW is high it may be due to:
    • Iron-deficiency anemia
    • Thalassemia intermedia

The main utility of RDW test is:

  • To discern between iron-deficiency anemia and thalassemia minor. In both cases hemoglobin and MCV are low but only in iron-deficiency anemia RDW is high.
  • To discern between macrocytic megaloblastic anemia (vitamin B12 or folic acid deficiency) from macrocytic non-megaloblastic anemia (alcohol, antivirals, etc.). In both cases hemoglobin is low and MCV is high but only in megaloblastic anemia RDW is high.

A very high level of RDW may be a sign of sideroblastic anemia.

Anisocytosis or a high RDW level in the blood means:

  • Mild anisocytosis (14.5 - 18 % in adults):

    RDW levels are slightly high. If only this parameter is over the limit is not a matter for concern. It may be due to infection, vigorous exercise or to certain drugs.

    If there is microcytic anemia (low hemoglobin and low MCV), it may be a first sign of iron deficiency anemia.

  • Moderate anisocytosis (18 - 26 % in adults):

    A moderate anisocytosis may be a sign of severe iron deficiency anemias (very low hemoglobin and low MCV) but is more characteristic of a megaloblastic anemia (due to vitamin B12 or folic acid deficiency) with a high MCV.

  • Severe anisocytosis (> 26 % in adults):

    A severe anisocytosis may be a sign of sideroblastic anemia.

    It can also be seen when hemoglobin is very low (below 6 mg/dl) in iron deficiency anemia (low MCV) and in megaloblastic anemia (high MCV).

    Another possibility is the existence of two different red cell populations, such as in a person that just received a transfusion. This can also happen when the person is under treatment for iron deficiency anemia or megaloblastic anemias. In this situation, RDW values can exceed 30% and it usually means a positive response to treatment.

Which factors can raise the RDW in a blood test?

There are some health circumstances than can raise your RDW level in the blood:

  • Alcohol
  • Blood transfusion

Which diseases can raise your RDW in a blood test?

The most common diseases why the RDW can be higher than normal are:

  • Iron-deficiency anemia
  • Megaloblastic anemia
  • Pernicious anemia
  • Sideroblastic anemia
  • Autoimmune hemolytic anemia
  • Thalassemia intermedia
  • Hemoglobin H
  • Myelodysplastic syndrome

What can I do to lower the RDW?

The RDW depends on numerous factors. For that reason, the best solution to improve in the long term the RDW level is to treat the underlying disease.

In fact, when a treatment for anemia is prescribed, at the beginning, it usually shows an increase in the short term that is usually a positive sign.

Where can I find more information about RDW level in the blood?

You can visit our pages about:

Which values are considered a high RDW level in the blood?

The following values are considered to be above the normal range:

IMPORTANT: These levels are expressed in %. They are an example of a healthy woman of about 45 years old with no known disease and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.

RDW
Mild anisicytosis
14.6 %14.7 %14.8 %14.9 %15 %15.1 %15.2 %15.3 %
15.4 %15.5 %15.6 %15.7 %15.8 %15.9 %16 %16.1 %
16.2 %16.3 %16.4 %16.5 %16.6 %16.7 %16.8 %16.9 %
17 %17.1 %17.2 %17.3 %17.4 %17.5 %17.6 %17.7 %
17.8 %17.9 %18 %     
Moderate anisicytosis
18.1 %18.2 %18.3 %18.4 %18.5 %18.6 %18.7 %18.8 %
18.9 %19 %19.1 %19.2 %19.3 %19.4 %19.5 %19.6 %
19.7 %19.8 %19.9 %20 %20.1 %20.2 %20.3 %20.4 %
20.5 %20.6 %20.7 %20.8 %20.9 %21 %21.1 %21.2 %
21.3 %21.4 %21.5 %21.6 %21.7 %21.8 %21.9 %22 %
22.1 %22.2 %22.3 %22.4 %22.5 %22.6 %22.7 %22.8 %
22.9 %23 %23.1 %23.2 %23.3 %23.4 %23.5 %23.6 %
23.7 %23.8 %23.9 %24 %24.1 %24.2 %24.3 %24.4 %
24.5 %24.6 %24.7 %24.8 %24.9 %25 %25.1 %25.2 %
25.3 %25.4 %25.5 %25.6 %25.7 %25.8 %25.9 %26 %
Severe anisocytosis
26.1 %26.2 %26.3 %26.4 %26.5 %26.6 %26.7 %26.8 %
26.9 %27 %27.1 %27.2 %27.3 %27.4 %27.5 %27.6 %
27.7 %27.8 %27.9 %28 %28.1 %28.2 %28.3 %28.4 %
28.5 %28.6 %28.7 %28.8 %28.9 %29 %29.1 %29.2 %
29.3 %29.4 %29.5 %29.6 %29.7 %29.8 %29.9 %30 %
30.1 %30.2 %30.3 %30.4 %30.5 %30.6 %30.7 %30.8 %
30.9 %31 %31.1 %31.2 %31.3 %31.4 %31.5 %31.6 %
31.7 %31.8 %31.9 %32 %32.1 %32.2 %32.3 %32.4 %
32.5 %32.6 %32.7 %32.8 %32.9 %33 %33.1 %33.2 %
33.3 %33.4 %33.5 %33.6 %33.7 %33.8 %33.9 %34 %
34.1 %34.2 %34.3 %34.4 %34.5 %34.6 %34.7 %34.8 %
34.9 %35 %35.1 %35.2 %35.3 %35.4 %35.5 %35.6 %
35.7 %35.8 %35.9 %36 %36.1 %36.2 %36.3 %36.4 %
36.5 %36.6 %36.7 %36.8 %36.9 %37 %37.1 %37.2 %
37.3 %37.4 %37.5 %37.6 %37.7 %37.8 %37.9 %38 %
38.1 %38.2 %38.3 %38.4 %38.5 %38.6 %38.7 %38.8 %
38.9 %39 %39.1 %39.2 %39.3 %39.4 %39.5 %39.6 %
39.7 %39.8 %39.9 %40 %40.1 %40.2 %40.3 %40.4 %
40.5 %40.6 %40.7 %40.8 %40.9 %41 %41.1 %41.2 %
41.3 %41.4 %41.5 %41.6 %41.7 %41.8 %41.9 %42 %
42.1 %42.2 %42.3 %42.4 %42.5 %42.6 %42.7 %42.8 %
42.9 %43 %43.1 %43.2 %43.3 %43.4 %43.5 %43.6 %
43.7 %43.8 %43.9 %44 %44.1 %44.2 %44.3 %44.4 %
44.5 %44.6 %44.7 %44.8 %44.9 %45 %45.1 %45.2 %
45.3 %45.4 %45.5 %45.6 %45.7 %45.8 %45.9 %46 %
46.1 %46.2 %46.3 %46.4 %46.5 %46.6 %46.7 %46.8 %
46.9 %47 %47.1 %47.2 %47.3 %47.4 %47.5 %47.6 %
47.7 %47.8 %47.9 %48 %48.1 %48.2 %48.3 %48.4 %
48.5 %48.6 %48.7 %48.8 %48.9 %49 %49.1 %49.2 %
49.3 %49.4 %49.5 %49.6 %49.7 %49.8 %49.9 %50 %
Medically reviewed by our Medical staff on 12/01/2021

Bibliography

  • A Manual of Laboratory and Diagnostic Test. 9th edition. Frances Fischbach. Marshall B. Dunning III. 2014. Pag 100. ISBN-10: 1451190891.
  • Laboratory tests and diagnostic procedures with nursing diagnoses (8th ed), Jane Vincent Corbett, Angela Denise Banks, ISBN: 978-0-13-237332-6, Pag. 35.

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