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 patient's blood.
Blood titer measurements can be very helpful in determining medical treatment. Antibody titers can tell the doctor if the patient has immunity 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.
Ashihara Y, Kasahara Y, Nakamura RM. Immunoassays and immunochemistry. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 44.
Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.