An RDW above about 14.5% is generally considered high, but there is no single RDW level that is automatically dangerous. The meaning depends on your laboratory’s reference range, your other blood test results, your symptoms, and your overall health.
An RDW blood test measures how much your red blood cells vary in size. Research shows that higher values are linked with worse outcomes in people who are seriously ill, including those with heart disease, severe infections, lung disease, or other conditions. However, RDW alone cannot diagnose a disease or predict what will happen to one person.
A mildly elevated result in someone who feels well may only require further evaluation. The same result may be more concerning in a hospitalized or critically ill patient. Rising RDW values over time may also be more important than one isolated test result.
Do not take iron, vitamin B12, folic acid, or other supplements without medical advice, since treatment depends on the cause. Discuss an elevated RDW with your primary care doctor, who may review the full blood count and order additional tests or refer you to a hematologist.