You will need to have a medical before your Embassy interview. The purpose of this medical we are told is to screen for communicable diseases. However, it is perfectly possible that they could be screening for absolutely anything. This having been said, even if you have genuine medical issues such as diabetes, arthritis, asthma, etc these are perfectly acceptable and would not pose a bar to admission as they are not communicable.

Within the Embassy package you will receive detailed instructions and to how to make your medical appointment.

Green Cards - US Citizen Married Alien Living Abroad Guide