Is there an at-home method for checking the health of your immune system?

Not exactly: A person with a healthy immune system fights infections well. In contrast a person with a weak immune system tends to have recurrent, severe or unusual infections. Infections that require hospitalization, IV antibiotics for treatment should make one think of immune problems. A list of 10 warning signs of immune problem go to: http://www.info4pi.org/library/educational-materials/10-warning-sign