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, and hepatitis. They can also help measure harmful antibodies related to lupus.
A titer measurement is expressed as a ratio, such as 1:40.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.