Hypertonicity and/or acidosis induce marked rheological changes under hypoxic conditions in sickle trait red blood cells.

Deformability and sickling of red blood cells (RBCs) from individuals with sickle cell trait (SCT) was evaluated under harsh biophysical conditions that mimic certain vascular beds in vivo. RBC deformability in osmotic-gradient ektacytometry was decreased in HbAS (SCT) compared to HbAA (wild-type) RBCs at supraphysiological osmolalities. RBC deformability was also measured by oxygen-gradient ektacytometry. Whereas RBC sickling was not observed under isotonic and neutral pH conditions, hypertonicity and acidosis alone or in combination induced reversible sickling of SCT RBC. These data suggest that hyperosmolality and/or acidosis enhance hypoxia-induced sickling of SCT RBC.