titer

A titer (or titre) is a measure of concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive reading. For example, positive readings in the first 8 serial twofold dilutions translate into a titer of 1:256 (i.e, 2⁻⁸). A specific example is a viral titer, which is the lowest concentration of virus that still infects cells. To determine the titer, several dilutions are prepared, such as 10⁻¹, 10⁻², 10⁻³,...,10⁻⁸.