Red cell distribution width (RDW-SD)
Blood cell systemRed Cell Distribution Width (Standard Deviation) is another measure of red blood cell size variation using standard deviation.
It provides similar information to RDW-CV but with a different calculation method.
Reference range
Female
Source: lab benchmark
Male
Source: lab benchmark
Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider.
Why this matters
RD-SD (Red Cell Distribution Width – Standard Deviation) provides early insight into changes in red blood cell production before symptoms appear. Elevated values can indicate nutrient deficiencies or other factors affecting blood health. Monitoring this marker supports timely dietary or lifestyle adjustments to maintain healthy red blood cell function.
How this connects to other biomarkers
- RDW-SD is an absolute measure of red-cell size variation, less influenced by mean cell size than RDW-CV.
- Elevated RDW-SD with normal RDW-CV can suggest a population of larger cells emerging (early macrocytosis) before overall MCV rises — useful for catching early Vitamin B12 / Folic acid (Vitamin B9) deficiency.
- Interpret alongside MCV, Ferritin, B12, and folate.
Included in
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