Does a thyroid ultrasound test for hyper or hypothyroidism?

Neither: A thyroid u/s tests for the texture and appearance of the gland. It can tell you if you have a growth on it or not. Sometimes an u/s can suggest hyper by the amount of blood flow going though it but it's not always accurate/reliable. I wouldn't use a thyroid u/s to test for hyper or hypo function. You need a blood test for that.

No: Ultrasound looks at structure. Blood test tells you function.