What is RDW?
RDW helps detect variation in red blood cells, which can support interpretation of anemia patterns. It is almost always interpreted with MCV and hemoglobin. Together with iron status and B vitamins, RDW can help clarify the most likely profile.
Why is RDW relevant?
RDW tells you whether your red blood cells are roughly the same size or vary widely. An elevated RDW means there is more variation in cell size — often an early signal that the bone marrow is producing cells under shifting conditions, for example with early iron deficiency or during recovery after blood loss. That makes RDW one of the markers that can change before MCV or hemoglobin move.
How to read RDW in context
RDW gains meaning together with MCV and hemoglobin: a low MCV with high RDW classically fits iron deficiency, while a high MCV with high RDW more often points to a B12 or folate issue. An isolated mildly elevated RDW without other abnormalities is often nothing serious yet, but warrants a follow-up measurement. Trends across a few measurements help distinguish a real shift from an incidental outlier.