How Can I Tell If My Parents Are Really My Parents?

QUESTION:

Dear Dr. Heller,

How can I find out if my parents are indeed my parents without asking them their blood type.  Even if I knew what their blood type is, how do I determine it?

Thank you.

ANSWER:

The blood type can prove one or more isn't your parent.  The only way to know for sure is to do expensive DNA testing.  There are no ways to do this without asking them.