A titer test (pronounced TIGHT er) is a laboratory test measuring the existence and level of antibodies to disease in blood. Antibodies are produced when an antigen (like a virus or bacteria) provokes a response from the immune system. This response can come from natural exposure or from vaccination.
It is a simple blood test but is expensive when sent out to a lab. Cost can run from $70 to $120 and up. (click HERE to read of less expensive in-house tests)