MMR Titer (Measles, Mumps and Rubella) Quantitative

Antibody testing may be used to confirm immunity, diagnose an active case, or to track outbreaks. Measles and mumps antibodies are virus-specific proteins produced by the immune system in response to an infection by the measles or mumps virus, or in response to vaccination.

This test check for IgG antibodies take a bit longer to develop, but once they do, they stay positive for life, providing protection against re-infection. 

An MMR titer test is typically ordered by healthcare workers and students studying in healthcare programs. Additionally, some people get the MMR titer to check immunity when they are going to be around a new baby or someone with a weakened immune system.