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RDW-SD Unit Converter
RDW-SD (Red Blood Cell Distribution Width – Standard Deviation) is a direct measurement of the variation in red blood cell size (anisocytosis). It is measured in femtoliters (fL) at the 20% relative height level of the RBC volume distribution curve.
Unlike RDW-CV, RDW-SD is not mathematically affected by the average size of the RBCs (MCV). This converter helps clinicians switch between the absolute measurement (RDW-SD) and the percentage-based RDW-CV, provided the patient’s MCV is known.
RDW-SD (fL)
AbsoluteStandard Deviation (Femtoliters).
RDW-CV (%)
Coefficient of Variation (Percentage).
Clinical Context
Reference Ranges:
• RDW-SD: Typically 39 – 46 fL.
• RDW-CV: Typically 11.5% – 14.5%.
Clinical Utility:
RDW-SD is often preferred in cases of pronounced microcytosis (low MCV) or macrocytosis (high MCV), as RDW-CV can be skewed by the MCV value. It is sensitive for detecting early Iron Deficiency Anemia.
Conversion Formula:
RDW-CV (%) = (RDW-SD / MCV) × 100.
RDW-SD (fL) = (RDW-CV × MCV) / 100.
Clinical References
How to Use This Converter
Follow these steps to convert RDW-SD values.
Set MCV
Ensure the MCV field matches the patient’s Mean Corpuscular Volume (default is 90 fL).
Enter Values
Input your laboratory result into the RDW-SD (fL) field.
Automatic Conversion
The calculator instantly derives the equivalent RDW-CV (%).
Reset
Use the Clear button to reset all fields.
Frequently Asked Questions
RDW-SD measures the actual width of the RBC distribution curve in femtoliters (fL) at the 20% height level, unlike RDW-CV which is a calculated percentage ratio.
No. RDW-SD is independent of MCV. However, RDW-CV is inversely proportional to MCV (CV = SD/MCV).