Low RDW in CBC Blood Test Explained

Many blood count tests today write the RDW as a part of the CBC test results, as below picture:

screenshot of low RDW value from a CBC test report

This screenshot of a RDW value in a CBC report shows:

  1. RDW: is a shortcode of the medical term “Red-blood-cell Distribution Width”, RDW represents the degree of variation of the sizes of red blood cells inside human blood, the normal range of RDW is 11.5% up to 14.5%,

The thalassemia trait doesn’t elevate RDW and still be normal, that why the normal RDW doesn’t exclude anemia.

High RDW appears when you have anemia due to iron deficiency, medically (a type of microcytic hypochromic anemia).

  1. The “L” letter beside the RDW value: means “low” as usually represented in the medical reports, Low RDW than the reference limits is medically insignificant because of inaccurate blood cell automatic counting or due to sampling errors or other hidden unattended errors in the procedures, thus why many clinicians don’t rely on RDW values.
  1. The reference range for RDW readings (11.5 – 14.5): doesn’t mean it is normal when your RDW lye inside this range, rather the RDW values within the reference range mean either normal size variation without anemia or means anemia with single size RBCs (i.e. thalassemia).

Does low RDW a valid indicator in diagnosis of anemia?

Should you worry when RDW level is low?

When your RDW value is below the limits, you shouldn’t worry because any tiny error in the testing procedures can result in such a falsely low result and can’t indicate a disease or a medical issue, and it’s beneficial to know that Low RDW value doesn’t necessarily mean that red blood cells are all in the small size, but the normal RDW is a more significant indicator of single size RBCs.

Did you understand yet what does high RDW means?

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