red blood cell morphological measurement red blood cell distribution width- standard deviation 2019-08-01T15:34:18Z CMO:0003232 EFO:0005192 EFO:0009188 RDW-SD Red blood cell distribution width- standard deviation (RDW-SD) is a measurement derived from the red blood cell distribution curves generated on automated hematology analyzers and is an indicator of variation in RBC size within a blood sample. The RDW is used along with the indices (MCV, MCH, MCHC) to describe a population of RBCs. The RDW measures the deviation of the RBC width, not the actual width or size of individual cells. The RDW-SD is an actual measurement of the width of the red cell distribution curve in femtoliters (fL). The width of the distribution curve is measured at the point that is 20% above the baseline. Since the RDW-SD is an actual measurement, it is not influenced by the MCV and more accurately reflects the red cell size variance. Red cell distribution width VT:0000248 clinical_measurement_ontology red blood cell distribution width sjwang