What is a titer?

Measure concentratn: A titer indicates the maximum serial dilution at which the substance is still detectable. For example, if I have antinuclear antibodies detectable in my serum at a titer of 1:40, it means i can dilute the serum 1:40 with Normal Saline (weak salt water) and detect them, but if 1:80, i cannot detect them. Titer has meaning entirely depending on context.

Dilution/concentrati: The term titer is usually used when the lab serially dilutes a specimen and tests for the presence of a substance, usually antibody. The highest dilution giving a positive results is called the tiler, e.G, if antibody is detectable at a dilution of 1:64, the specimen is said to have a titer of 64.