Prolonged in vitro survival of human neonatal platelets. In vitro survival of human neonatal and adult platelets was evaluated by incubating PRP from human umbilical CB and adult PB at 37°C for 5 days. (A) Annexin V-binding and P-selectin expression were evaluated daily by flow cytometry in CD41-gated CB and PB platelets during a 5-day incubation period. (B) Percentages of Annexin V positive platelets were quantified daily and compared between CB-PRP (n = 6) and PB-PRP (n = 8). (C) Platelet survival was quantified daily by FACS analysis after staining with the mitochondrial dye JC-1. The percentages of live platelets were measured in CB-PRP (n = 3) compared with PB-PRP (n = 5). *P < .05; **P < .01; ***P < .001.