Can someone tell me how you handle this standard in your SOP?

Interpreation criteria shall be established to prevent mistyping of Rh negative patient as Rh positive due to exposure to Rh positive red cells.

I have the following statement in my Rh Typing Procedure:

If patient results are less than 2+, or mixed field, obtain patient transfusion/pregnancy history in order to prevent mistyping a D-negative patient as D-positive due to recent exposure to D-positive red cells.