is life-threatening (at risk of death at the time of the adverse event, not an event which could™ hypothetically have caused death if it were more severe),
requires hospitalisation or extension of existing inpatients™ hospitalisation,
results in a persistent or significate disability or incapacity, or
is a congenital anomaly or birth defect.
Other events such as those requiring emergency intervention to prevent one of the serious outcomes described above might also be reported as a serious adverse event.