Here is a recursive version.

bool isSorted(const Cell* L)
{
  if(L == NULL) return true;
  else if(L->next == NULL) return true;
  else if(L->item >= L->next->item) return false;
  else return isSorted(L->next);
}

Here is a looping version.

bool isSorted(const Cell* L)
{
  if(L == NULL) return true;

  const Cell* p = L;
  while(true)
  {
    if(p->next == NULL) return true;
    else if(p->item >= p->next->item) return false;
    else p = p->next;
  }
}