The irreversibly sickled cell.

The characteristics of irreversibly sickled cells (ISC) are reviewed in relationship to their potential significance in the initiation of sickle cell vaso-occlusion. Although ISC are implicated in the shortened red cell survival of sickle cell anemia, there is no direct correlation to the frequency or severity of sickle crisis. ISC are heterogeneous in their physical properties suggesting the possibility that a subpopulation may be disproportionately important in causing vaso-occlusion. Study of their deformability heterogeneity of ISC showed that filtration-separated hard ISC are similar in morphology and intracellular composition to soft ISC, and would not be distinguished on blood smear.