bamboojoe,
OK, let's give you a choice.
You can invest in one of two companies.
The first has an accurate test that can tell if you have cancer or not.
The second company is marketing a test that is not as accurate as the test from the other company.
Now secondly, you ask what amount of liability a doctor has for making a diagnosis using a less than accurate test. The test could be given but it would just confuse the patient and be a waste of time and money because it would have to be following by the most accurate test available. If the doctor did not give the more accurate test, he would be insane.