Platelet kinetics.

Platelet survival can be determined with considerable precision using radioisotopic methodologies; however, complications associated with these techniques still catalyze the search for nonisotopic procedures to estimate platelet survival as well as surrogate markers of platelet life span. Recent reports on markers of platelet age have focused on thiazole orange-staining for enumeration of "reticulated platelets," ie, young platelets with residual mRNA. Numerous clinical studies have observed a correlation between thiazole orange-positive platelets and platelet synthesis, thereby providing a noninvasive means to differentiate between synthetic and destructive mechanisms in thrombocytopenia. Additionally, nonisotopic methods for quantitating platelet survival have recently been developed in animal systems, although they have not yet been transferred to human use. And finally, an ancillary topic related to platelet turnover is the impact of cell age on platelet reactivity. Prevailing paradigms concerning age and reactivity are complicated by recent studies with cytokines, such as interleukin-6, which demonstrate that platelet age is not the sole determinant of platelet reactivity.