Titer test

Do you know where to find your childhood vaccination records?

For many people, the answer is no. Because routine vaccines are often given during early childhood and the records are then stowed away by parents or given to schools for enrollment, many adults have never even seen their own. So, when there’s a disease outbreak, how do you know if you have immunity?

“There are two main ways for someone to be immune: they’ve received a vaccine or had a previous infection,” explained Shalika Katugaha, MD, system director of Infectious Diseases for Baptist Health. “If the illness or vaccination happened when you were young, you may not remember it. That’s why antibody titer tests are so valuable.”

Blood titer: Analyzing antibodies

An antibody is a protein that binds to an antigen, like a virus or bacteria, and coordinates the immune response against it.

“An antibody titer test, also called antibody serology test, is a blood test that measures the presence and concentration of specific antibodies against a particular pathogen or antigen in the blood,” said Dr. Katugaha. “The term ‘titer’ refers to the measure of how many antibodies are in the blood.”

The most common form of antibody titer testing is done through a blood draw. Antigens are placed on a solid surface and the patient’s blood is added. If antibodies are present, they stick to the antigen, and a labeled secondary antibody makes them visible.

The presence of antibodies signals that the person is immune to that particular virus, bacteria or other antigen.

Who should get an antibody titer test?

A doctor may order an antibody titer test to:

• Determine if someone has sufficient immunity to a disease from a past vaccination or infection.
• Ensure a previous vaccination was effective, which is particularly important for health care workers or immunocompromised persons.
• Diagnose past or current infections by seeing if there are antibodies weeks to months after an infection.
• Screen for autoimmune diseases by checking antibodies that attack the body’s own tissues.
• Meet requirements for school, health care facilities or employment.

“The most tested group of people is health care workers,” said Dr. Katugaha. “The Advisory Committee on Immunization Practices (ACIP) recommends that all health care workers have evidence of immunity to measles, mumps, rubella and varicella [chickenpox].”

Antibody titer testing is also important for immunocompromised individuals, such as those who have undergone a stem cell or solid organ transplant, have HIV, are undergoing hemodialysis for kidney conditions or are taking medications that suppress the immune system.

“People who don’t know their vaccination status may also want to pursue an antibody titer test in certain situations,” Dr. Katugaha said. “This includes pregnant women or those who may become pregnant to assess the risk of passing rubella to an unborn child, which can cause miscarriage or stillbirth. People who live with or have sexual contact with individuals with hepatitis B may also want to confirm their immunity to the disease.”

For which diseases can antibodies be tested?

“Antibody titer testing is available for numerous vaccine-preventable, infectious and autoimmune diseases,” said Dr. Katugaha.

Common vaccine-preventable diseases include:

• Measles
• Mumps
• Rubella
• Varicella-zoster (chickenpox and shingles)
• Hepatitis A and B
• Tetanus
• Diphtheria
• Pertussis (whooping cough)
• Polio
• Rabies
• Yellow fever
• Haemophilus influenzae type B

“Antibody serology testing can help diagnose or assess immunity for infectious diseases like COVID-19, Lyme disease, toxoplasmosis, mononucleosis (Epstein-Barr virus), cytomegalovirus and HIV,” said Dr. Katugaha.

Additionally, autoantibody testing can be conducted for diseases like systemic lupus erythematosus, rheumatoid arthritis, celiac disease and thyroid disorders.

Assessing immune status accuracy

Dr. Katugaha cautioned that the presence of antibodies doesn’t always mean you’re protected.

“While antibody levels correlate with decreased risk of infection, even high titers can fail to prevent infection when exposure intensity is high or when there are variants that can evade immunity,” she said. “Additionally, our bodies contain antibodies called polyvalent antibodies that can bind to multiple antigens. This can lead to false positive tests.”

Timing is key when it comes to antibody serology testing; when performed within the first 10 days of the onset of an illness, test results may come back falsely negative because the immune system hasn’t yet produced detectable antibodies. For vaccines, testing should be done one or two months afterward to allow time for antibodies to develop.

Dr. Katugaha emphasized that while testing your immunity may be warranted in certain situations, it’s not necessary for healthy adults and children after standard vaccination.

If you’re unsure of your vaccination status, talk with your primary care physician about whether an antibody titer test may be right for you. If you’re looking for a new provider, use our Find a Doctor tool or schedule an appointment online.