RDW-SD Test
The free oxygen that passes into the blood through the lungs is stored in the blood by the erythrocytes and transported to the tissues, and the carbon dioxide in the tissues is delivered back to the lungs. Whether there are size differences in the distribution of erythrocytes in the blood, which has the most important role in this mechanism, is revealed by the RDW test of erythrocyte distribution width.
Normally, mature erythrocytes in the blood are expected to be the same size. As the size of the erythrocytes changes, both their capacity and functions will be affected, which can cause many diseases. In addition, many diseases cause these size differences and realize their symptoms. For example, before anemia appears in the blood, the size of the erythrocytes and the RWD value begin to increase. Because less production of young erythrocytes causes an increase in the number of mature erythrocytes and a relative increase in erythrocyte sizes. While RWD is normal in thalassemia carrier, RWD value increases in iron deficiency anemia. RDW values are used to evaluate many medical conditions, including anemia.
RDW (erythrocyte distribution width) is also evaluated with different tests with different interpretations of the sizes of erythrocytes. The main ones are RDW-CV and RDW-SD.
The reference region is generated from a horizontal baseline of 20% with a horizontal peak of 100% in the red cell distribution curve, and the different cell volumes in this twenty percent region are reported. If the erythrocytes are close to each other in size, RDW-SD is low, but if their size is different from one another, it is considered to be high RDW-SD. RDW-SD indicates standard provisioning. The RDW-SD is the actual measurement of the width of the red blood cell distribution curve in femtoliters. Because RDW-SD is an original measurement, it is unaffected by MCV and more accurately expresses red cell size variance.
Normal values of RDW-SD are 37-54 fL. This is a measure of volume called the femtoliter and is denoted by the abbreviation fL. Normal RDW-SD values of 29-46 fL are also considered in some centers. There are also centers that accept 40-55 fL for adults.
The RDW-SD test is among the tests that allow much more accurate evaluations than the RDW test. RDW-SD was found to be more accurate in estimating the course of existing diseases and mortality. RDW-SD is generally used to determine prognosis. Instead of evaluating it alone, it is interpreted together with other examinations and the patient’s clinic.