You should consider testing for lead if there are children in your home and your house was built before 1978, or your house is near a freeway or busy roadway where leaded gasoline and its exhaust may have polluted the soil with lead.
If your house was built before 1978, it is especially important to test for lead if...
your house has peeling or chipping paint;
your house has bare soil in the yard where children play;
you plan to repaint, remodel or renovate the house;
a child living in the house has had a blood lead test result indicating lead exposure
your house was built before 1950 -- such homes almost always have some lead-based paint.