Where in the report?
What Datatype is [TissueSent]? Yes/No? Text?
Add 2 unbound controls to the Report Footer section.
Assuming "Yes" or "No" as text datatype:
= Sum(IIf([TissueSent] = "Yes",1,0))
= Sum(IIf([TissueSent] = "No",1,0))
Assuming Yes or No as in a Yes/No field:
=ABS(Sum([TissueSent])) (For Yes)
=Sum([TissueSent]+1) (For No)