An antibody count used to indicate immunity to a particular disease is called what?

• A. Titer
• B. Antibody titer
• C. Antigen level
• D. Immunity index

Answer: (A)

The main idea is that a titer is a measurement of how concentrated a person’s antibodies are in their blood. In practice, a serologic test dilutes a patient’s serum step by step to see how much antibody remains able to react with a specific disease antigen. The highest dilution that still produces a detectable reaction defines the titer. A higher titer means more antibodies and a greater likelihood of immunity, though the protective level depends on the disease and other immune factors.

Antibody titer and titer refer to the same concept, but the concise term used in this context is titer. Antigen level would measure pieces of the pathogen itself, not the person’s immune status, and immunity index isn’t a standard clinical term for this purpose.