How often are post mortem results deemed permanently inconclusive?

[Tuesday83]

(I know this is a long shot and in reality I need to ask a Pathologist, but here's hoping there is one on here!)

I am asking purely because my friends sister died almost four months ago now, and after two autopsies, she says they never concluded a cause of death. How often does this happen?
She died in her sleep and that is seemingly all they know.

[Mamyalynne]

Sounds like suddaen adult death, similar to cot death in babies and often no clear cause is found. I don`t know if there is a way of checking the stats for PM results and am sure such a conclusion can seem very unsatisfactory to the family though.

[Mamyalynne]

sudden ^

[Sqad]

I am not a Pathologist but:

1) This situation of "no cause of death" in my opinion is very unusual.
2) I am not sure that in such a case a death certificate cannot be given.
3) No death certificate, then no burial or cremation.

These are my comments, but I stand to be corrected.