Red cell distribution width parallels dense red cell disappearance during painful crises in sickle cell anemia

We reported previously that painful crises in patients with sickle cell anemia are accompanied by striking decreases in the percent of densest red cells (fraction 4) when studied with isopyknic Percoll-Stractan gradients. We report that an alternative to density gradients is the red cell distribution width (RDW), an estimate of red cell size variation measured with a Coulter counter. In 17 painful crises in 12 patients with homozygous sickle cell anemia the RDWs decreased in each crisis, from an initial mean of 16.2 +/- 1.8 SD to 12.8 +/- 1.3 (P less than 0.001). In patients in whom serial measurements of both RDW and fraction 4 (very dense) red cells were taken during crisis, the two measurements declined in parallel. The decrease of RDW is a readily observable and objective laboratory concomitant of painful sickle crisis.