This isn't as cut and dried as you might think. Many countries, such as Spain, have an opt-out rather than an opt-in process for organ donation.
Spain (and many other countries) decided that they would rather be opt-out, so by default you've consented. This is actually a great example of the power of defaults to affect an outcome. Because of this out-out, the number of donations increases significantly.
I'd be more interested to know what happens to foreigners. I suspect that they aren't treated as consenting, but I don't know.