Definition
What RDW measures
Red cell distribution width measures the variation in red-cell size. A uniform population reads low; a mix of small and large cells reads high.
Illustrative sample band · Synthetic
13%
11Sample target 12–14 %15
Why it matters
How clinicians usually read it
It can be an early-change flag: rising size variation sometimes precedes visible drops in hemoglobin, and it helps separate mixed causes of anemia.
When it reads low
A lower value can mean
A low RDW simply means uniform cell sizes and is not a clinical concern.
When it reads high
A higher value can mean
A higher RDW means a mixed population — often a recovering or developing deficiency (iron, B12) or recent transfusion. It prompts a look at the indices and iron studies.
Questions for a clinician
Bring the number into a real conversation
01
Does a high RDW here suggest an early or mixed deficiency?
02
Which of my other markers best explains the size variation?
03
Is this worth re-checking sooner than the usual interval?
Educational boundary
Educational information only. Displayed ranges are illustrative sample bands, not a diagnosis, treatment plan, or substitute for the contracted laboratory report and a qualified clinician.
See it as a sample result
The sample dashboard shows an illustrative reading, target band, and trend for RDW.