RDW 15.5 %

An RDW of 15.5 % is mildly above the common 11.5–14.5% range, but some labs count values up to 15% or slightly higher as normal. Check your own report's reference range, and look at your hemoglobin and MCV — if those are normal, a value in this zone is often not significant.

At 15.5 %, the elevation is mild. This can be one of the earliest signs that iron, B12, or folate stores are running low — sometimes before hemoglobin drops — but it can also be normal by your lab's cutoff. It is a reasonable thing to raise at a routine visit rather than a cause for worry.

Yes. RDW often rises before hemoglobin falls, so a high RDW with normal hemoglobin can be an early warning that iron, vitamin B12, or folate stores are running low. It can also follow recent blood donation or blood loss that your body is already correcting. A simple set of follow-up tests — usually ferritin, B12, and folate — can check for a developing deficiency before it becomes anemia.

No. A low RDW simply means your red blood cells are very uniform in size, and no disease is diagnosed from a low RDW alone. If your hemoglobin, MCV, and the rest of your CBC are normal, a low RDW needs no follow-up beyond mentioning it at your next visit.

With a mild elevation like 15.5 %, the first step is finding out whether anything needs fixing at all — this zone is normal at some labs. If your clinician finds early iron or vitamin deficiency, correcting it through diet or supplements typically returns RDW to normal within a few months.

Both measure the same thing — variation in red cell size — but on different scales. RDW-CV is a percentage (typical adult range about 11.5–14.5%) and is what most US labs report as 'RDW.' RDW-SD is reported in femtoliters (fL), with a typical range of roughly 39–46 fL, and is less affected by the average cell size. If your report shows a number in the 40s with 'fL' next to it, you are looking at RDW-SD, and percentage-based ranges do not apply to it.

Almost never. The overwhelming majority of high RDW results are explained by iron, B12, or folate deficiency, blood loss, or chronic illness — not cancer. Research has linked higher RDW to worse outcomes in various diseases, but that makes it a general, non-specific marker of illness and inflammation, not a cancer test. In older adults with a persistently high RDW and other unexplained CBC abnormalities, clinicians may check for bone marrow disorders, which is one reason follow-up matters — but a high RDW by itself is not a reason to fear cancer.