Titer: The concentration of a substance in a fluid, such as the concentration of an antibody in blood. The titer reflects the amount of the substance in the fluid. Sometimes also spelled titre. SLIDESHOW Could I Be Allergic? Discover Your Allergy Triggers See Slideshow From Allergies Resources Learn How to Treat Chronic HivesElimination Diet for EoE Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19