A titre (also spelled “titer”) is a measurement of how much of a specific antibody is circulating in your blood. It’s determined by repeatedly diluting a blood sample until the antibody can no longer be detected, then reporting the last dilution where it was still present. The result is expressed as a ratio like 1:40 or 1:320, and it tells your doctor whether you’re immune to a disease, fighting an active infection, or showing signs of an autoimmune condition.
How the Test Works
A titre test starts with a standard blood draw. In the lab, technicians take your serum (the liquid part of blood after clotting) and dilute it in a series of steps. They mix a small amount of serum with a buffer solution, then take a portion of that mixture and dilute it again, repeating the process across multiple tubes or wells in a plate. Each step cuts the concentration roughly in half.
At each dilution, the lab checks whether the target antibody is still detectable. The titre is the highest dilution at which the antibody still shows a positive reaction. So a result of 1:320 means the antibody was still detectable even when the blood was diluted 320 times. That’s a much stronger antibody presence than a result of 1:40, where the antibody disappeared after just 40-fold dilution. Higher ratios mean more antibodies in your blood.
Reading the Numbers
Titre results are reported as ratios that double at each step: 1:40, 1:80, 1:160, 1:320, 1:640, and so on. The numbers can feel counterintuitive at first. A “higher titre” means a larger second number, which indicates a greater concentration of antibodies. A 1:640 result reflects roughly 16 times the antibody concentration of a 1:40 result.
What counts as a “positive” result depends on the test. For antinuclear antibody (ANA) testing, which screens for autoimmune conditions like lupus, some labs set the positive threshold at 1:160. A low ANA titre on its own, without other symptoms, carries very low risk of developing an autoimmune disease later. For vaccine immunity checks, the result may simply be reported as positive or negative, meaning your antibody level is either above or below a protective threshold.
Why Your Doctor Orders a Titre
Titre tests serve three main purposes: checking immunity, diagnosing infections, and screening for autoimmune disease.
- Vaccine immunity verification. Schools, employers, and healthcare facilities often require proof of immunity to diseases like measles, mumps, chickenpox, hepatitis B, and rubella. If you’ve lost your vaccination records or need confirmation that a vaccine actually produced a protective response, a titre test can provide that answer. A positive result means you have adequate immunity. A negative result means you’ll likely need a booster or a new vaccine series.
- Infection diagnosis. When a doctor suspects an active or recent infection, they may order two titre tests spaced weeks apart. The first is drawn during the early phase of illness and the second is drawn 2 to 10 weeks after symptoms resolve. A fourfold or greater rise in titre between the two samples, say from 1:64 to 1:256, confirms that your immune system was actively responding to that specific pathogen. The CDC considers this paired-sample approach the most conclusive method for confirming certain infections.
- Autoimmune screening. ANA titre testing helps identify conditions where the immune system mistakenly attacks the body’s own tissues. Elevated titres, especially at 1:160 or above, prompt further investigation into conditions like lupus or rheumatoid arthritis.
Quantitative vs. Qualitative Results
Not every antibody test produces a titre. Some tests are qualitative, meaning they report only whether antibodies were detected or not, with no information about how much is present. These are simpler and faster but less informative.
Quantitative tests, by contrast, produce a numeric result that can be tracked over time and compared between different labs, as long as the tests are calibrated to the same reference standard. Your doctor might choose a quantitative test when monitoring how your antibody levels change, such as tracking immune response after vaccination or watching whether autoimmune antibodies are rising or falling with treatment.
What Can Affect Your Results
Several factors can push titre results higher or lower than they’d otherwise be. Immunosuppressive medications have a significant impact, particularly on antibody levels after vaccination. People taking these drugs often produce a weaker immune response, which shows up as a lower titre even when vaccination was successful.
Timing matters too. Antibody levels naturally decline over months and years after vaccination or infection, so a titre drawn years later may be lower than one drawn shortly after. Interestingly, longer intervals between vaccine doses tend to produce stronger antibody responses to subsequent boosters. Regular alcohol consumption has also been linked to reduced antibody levels after vaccination, though common conditions like high blood pressure and diabetes don’t appear to meaningfully affect results.
How Long Results Take
Turnaround time varies by the type of test and the lab processing it. Routine titre tests for vaccine immunity often come back within a few days from commercial labs. More specialized testing takes longer. Measles antibody testing at a CDC reference lab, for instance, has a 7-working-day turnaround for standard antibody detection and up to 30 working days for more advanced testing that evaluates how strongly antibodies bind to the virus. Your provider or lab can give you a more specific timeline based on the test ordered.
Titre vs. Immunity
A positive titre generally means you have protection against a specific disease, but antibody levels are only one piece of the immunity puzzle. Your immune system also relies on memory cells that can rapidly produce new antibodies when re-exposed to a pathogen, even if circulating antibody levels have dropped below detectable thresholds. This is why some people with low or negative titres may still mount a protective response upon re-exposure, and why a negative titre doesn’t always mean you’re completely unprotected. It does, however, mean that measurable circulating defense is absent, which is why schools and workplaces typically require revaccination when titres come back negative.