One of several tests included in acomplete blood count (CBC), RDW is measured as a percentage.
The normal range for RDW in adults is 12% to 15%.
However, the reference range can vary based on the lab.
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A high RDW may be a sign of a nutrient deficiency.
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When Is an RDW Blood Test Needed?
It is also known as erythrocyte distribution width or RDW-SD (standard deviation test).
RDW test results will be considered alongside other CBC results as a healthcare provider evaluates your situation.
RDW can also be very helpful in mixed anemias.
The RDW can predict the overall risk of mortality in people over the age of 45.
What Are the Risks of a RDW Blood Test?
Since the RDW is part of a simple blood test, there are few risks.
Here is what to expect before, during, and after the blood draw.
They will then insert the needle through your skin and into the vein.
After the sample is removed, the needle is removed, and pressure is applied to the puncture wound.
A dressing is then applied to keep the area clean and reduce any bleeding.
Interpreting RDW Test Results
RDW results appear on a CBC report alongside all of the other indices.
The combination of results is usually used rather than the RDW alone.
Normal red blood cells average between 6 and 8 micrometers in diameter.
RDW results are given as a percentage.
Some lab references ranges go as low as 11.5% or as high as 15.4%.
Here’s a sense of the possible reasons why your RDW may be low, high, or normal.
Low RDW
Having a low RDW is normal and ideal.
It means that your red blood cells are all uniform in size and shape.
A low RDW is not associated with any blood disorder.
The following are examples of conditions that combined RDW and MCV rates may indicate.
Note, however, that there are exceptions to these general rules.
This test is usually done after a CBC to investigate an abnormality.
In a peripheral blood smear, the blood sample is viewed under the microscope.
It may have a wide range of uses even when a person’s red blood cell count is normal.
In addition to the conditions mentioned above, some argue that RDW could be a measure of general well-being.
It has also been linked to certain conditions unrelated to blood, such assleep apneaandlupus.
A high RDW alone cannot diagnose these conditions, however.
2019;86(3):167-172. doi:10.3949/ccjm.86a.18072
Kaiser Permanente.Complete blood count (CBC).
2006 Dec;4(4):342].Clin Med Res.
2014;3(4):e001109.
2015;100(10):e387-e389.
2018;38(6):503-511. doi:10.3343%2Falm.2018.38.6.503
Cleveland Clinic.RDW blood test.
National Library of Medicine.Anemia screening.
Loprinzi PD.Sleep duration and sleep disorder with red blood cell distribution width.Am J Health Behav.
2018;3:73. doi:10.21037/jlpm.2018.08.03
Penn Medicine.What is anemia?
McPherson RA, Pincus MR, eds.Henrys Clinical Diagnosis and Management by Laboratory Methods.
