This test is the critical tool for diagnosing a current or very recent Rubella infection. It detects the "first-responder" (IgM) antibodies your immune system creates when it first encounters the virus. This test is time-sensitive and essential if you are pregnant and have been exposed to Rubella or develop a rash. A positive result signals an active infection that requires immediate medical attention. A simple blood draw provides the fast, 'real-time' answer your doctor needs to protect your health and your pregnancy.