What is the term for determining antibody concentration by serial serum dilutions?

• A. Antibody titration
• B. Antibody titer
• C. Serum dilution assay
• D. Immunoglobulin quantification

Answer: (A)

Antibody titration is the process used to determine how much antibody is present by testing a series of serum dilutions. You dilute the serum step by step and assay each dilution; the farthest dilution that still yields a positive reaction defines the titer. The titer is the reciprocal of that dilution, so a positive result at 1:128 but not at 1:256 corresponds to a titer of 128.

This differs from antibody titer, which is the numerical value obtained from the test (the result), not the method itself. A term like serum dilution assay isn’t the standard name for this technique, and immunoglobulin quantification refers to measuring total immunoglobulin levels rather than determining a specific antibody concentration through serial dilutions.