A titre usually refers to a blood test that measures the concentration of substances in a person's blood. The test can be used to determine if a person has developed immunity to specific diseases, checking for the necessary concentration of antibodies for immunity. Titres are also used to check the concentration of viruses or bacteria in the blood, as well as other substances.
The most common use of titre testing is antibody testing. An antibody is a special kind of protein created by the immune system to fight infection. In order for a person to be immune to a specific illness, they need to already have antibodies to the illness causing agent in their blood. These antibodies can come from previous exposure to an illness causing bacteria or virus, or from vaccination. For there to be immunity, antibody levels need to reach concentrations that are specific to each illness.
Having the kind of information that titre testing provides can be extremely useful. It can help health-care professionals decide if vaccination was effective, or if booster shots are needed. It can also help determine if a person who was exposed to an illness-causing agent gained immunity from exposure or should be vaccinated anyway. A titre can also be used to prove immunity if vaccination records are lost, eliminating the need for additional vaccinations. Some antibodies commonly tested include measles, mumps, rubella, varicella or chicken pox, polio, hepatitis B and C, and others.
Another use for a titre test is to confirm a diagnosis of illness by checking the concentration of viruses or bacteria in the blood, or by checking the antibodies to that agent. Some illnesses where this can be useful include mononucleosis, Lyme disease, or hepatitis. It can also be used to check the immune system responses in autoimmune disorders such as lupus, where the immune system is attacking the body's own tissue. The concentrations of chronic disease causing agents such as the HIV virus can also be monitored using a titre, this is also known as viral load testing.
The test is actually a very simple procedure for the patient, with little risk involved. Blood is most often drawn from the arm, either inside the elbow, or on the back of the hand. The patient is seated comfortably and the area is cleaned with antiseptic, then an elastic band is used to restrict blood flow and make the veins swell and pop up a little, making the vein easier to get a needle into. Once the vein is ready, a needle is inserted to collect blood from the vein into an attached vial or tube, then the elastic band is taken off the arm.
After enough blood is collected the needle is removed, then the vial is labeled and sent for testing. The titre testing is performed at a laboratory and the results are sent to the patient's doctor. The doctor evaluates the results and uses the information to make treatment decisions.