Educational information only. At Precursor, blood testing is requested and reviewed by a clinician and considered alongside your history and other markers, not as a stand-alone diagnosis. Testing is performed in NATA-accredited laboratories to ISO 15189 standards.

What is RDW?

RDW, or red cell distribution width, measures how much your red blood cells vary in size. Where MCV gives the average size, RDW describes the spread. A high RDW means your red cells are a more mixed collection of large and small, rather than a uniform population.

Why it matters

RDW adds a useful extra dimension to the blood count. A raised RDW can be an early clue to a developing nutritional deficiency, and combined with MCV it helps a clinician distinguish between different causes of anaemia more precisely.

What your results can mean

Higher than optimal

A high RDW indicates a wide range of red cell sizes, which can occur early in iron, B12 or folate deficiency, sometimes before other markers shift. It is read alongside MCV and your nutrient levels.

Within the healthy range

An RDW in range suggests a fairly uniform red cell population, which is the usual, reassuring picture.

Reference ranges in Australia

RDW is reported as a percentage (%), with laboratory-specific reference ranges. Read your result against the range on your own report and alongside your MCV.

Test your blood count with Precursor

RDW is most useful read with MCV and your nutrient markers. At Precursor it is measured as part of Full Advanced Bloods, a single clinician-reviewed blood draw covering your full blood count, iron, vitamins and other markers together, giving you and your clinician a broad baseline to understand and track.