A titer is a measurement of the amount or concentration of a substance in a solution. It usually refers to the amount of antibodies found in a person's blood.
Blood titer measurements can help determine medical treatment. Antibody titers show if a person is immune to diseases such as measles, chickenpox, or hepatitis. They can also help measure harmful antibodies related to lupus.
A titer measurement is expressed as a ratio, such as 1:40.
Aoyagi K, Ashihara Y, Kasahara Y. Immunoassays and immunochemistry. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 45.
Review Date: 11/4/2021
Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.