What's the most common verb to use when you are undergoing medical exams?

I think you can say the following:

I'm at the hospital, doing medical exams.

I'm at the hospital, undergoing medical exams.

I'm at the hospital, having medical exams.

I'm at the hospital, taking medical exams.

I'm not very sure if some of them may be confused with taking a written medical exam (you can't discard the possibility that someone could be at the hospital writing a exam).

Which of them is less ambiguous? Is there a better choice?

In the US, a very common way to express this concept is

I'm at the hospital for tests.

No one would think you either are taking a non-medical exam or administering one.

You could say

"I'm at the hospital having a check-up."

You can also replace "check-up" with medical or physical where it is implicit that you are referring to a an examination of your health and not a test of your medical knowledge.