Demonstration that thiazole-orange-positive platelets in the dog are less than 24 hours old.

Approximately 6% of dog platelets are positive for staining with thiazole orange, a dye frequently used to stain ribonucleic acid. In this report, thiazole-orange positivity is shown to mark platelets that are less than 24 hours old. Dog platelets were derivatized in vivo with N-hydroxysuccinimido biotin such that greater than 95% of all platelets were biotinylated. Newly synthesized, nonbiotinylated platelets were then monitored by flow cytometry for their ability to bind thiazole orange. After biotinylation, the percentage of biotin-negative, thiazole-orange-positive platelets increased gradually from 0.72% at 30 minutes to 5.44% at 24 hours. These data indicate that thiazole-orange staining does label newly synthesized platelets.