RDW

RDW reflects the variation in red blood cell size and is mainly used to interpret anemia patterns together with hemoglobin, MCV, and other CBC indices. It is a supportive marker rather than a standalone diagnostic test.
Also known as:
Red blood cell distribution width
.

RDW ranges

Interpret your result
"Normal" lab range for RDW is between 11.5 and 14.5 %:
11.5
14.5
According to OptimalDX, RDW should be between 11 and 12.6 %:
11
12.6
According to Tonelli M. et al. (2019), RDW should be below 12.6 %:
12.6
Optimal range
Optimal range for RDW appears to be between 11 and 12.6 %:
9
11
12.6
14.5
18
Why this optimal range?
Preliminary range is based on functional health organizations including but not limited to those listed above.

Low RDW

Common reasons for low RDW:

  • Low RDW usually reflects uniformly sized red blood cells. It is infrequent and clinically meaningless.

    In context, it can be seen when erythropoiesis is stable and there is no meaningful nutrient deficiency signal in the CBC pattern.

High RDW

Common reasons for high RDW:

  • High RDW is commonly seen with iron, folate, or vitamin B12 insufficiency, mixed anemia patterns, inflammation, and recovery phases after blood loss or treatment.

    Higher RDW has also been associated with worse cardiometabolic and mortality outcomes in cohort studies, so it should be interpreted with hemoglobin, MCV, ferritin, B12, and inflammatory markers.

    ,

Images:

High RDW was associated to substantial rise in all-cause mortality.

High RDW was associated to substantial rise in all-cause mortality.

Red: adjusted for demographics; Blue: adjusted for demographics and all 30 baseline morbidities. Green: fully adjusted (demographics, morbidities, and baseline HGB, WBC, and eGFR.)
RDW increases with age

RDW increases with age

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