They look to the Occupational Outlook Handbook and other publications by the US Department of Labor. Since nurses require only a 2 year degree, they do not even require a college degree let alone a masters.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.