Can a thyroid biopsy's produce false results?

Thyroid biopsy: Hard to answer. No test is perfect. With an ultrasound-guided needle bx, the pathologist looks at the sample of cells that he gets. He may not get a good sample. In some kinds of thyroid cancer, it is hard to distinguish normal from abnormal cells. Sometimes decisions need to be made in spite of "test results", i.e. A judgement call. Talk to your endocrinologist.