test if update statement did anything in a transaction?

Is it possible to check if an update statement did anything in a
transaction?

ie
begin;
update table set intfield = intfield+1 where intfield >= 1;
case rowsaffected > 0
raise error;
end;
insert into table (intfield) values (1);
commit;

in plpgsql there's the found variable to test. is there an equivalent
in a transaction?

TIA,

klint.