Antibody titer tests measure the level of antibodies in the blood to analyse immunity against specific infectious diseases. They provide guidance on protection status and the potential need for vaccination or booster immunization.
What is an Antibody?
An antibody, also known as an immunoglobulin, is a Y-shaped protein produced by the immune system in response to exposure to a foreign substance called an antigen. Antibodies play an important role in the body's immune response. Here are some key facts about antibodies:
- Antibodies are secreted by plasma cells, which are a type of white blood cell produced from B lymphocytes (B cells).
- They have a unique structure that allows them to bind specifically to their target antigen. This helps the immune system identify and neutralize threats like bacteria, viruses, and toxic substances.
- Binding to an antigen triggers other immune responses such as complement activation, opsonization for phagocytosis, and antigen neutralization.
- Antibodies also stimulate removal of antigens by attracting macrophages and other cells to digest them.
- There are 5 major classes of antibodies: IgG, IgA, IgM, IgE, and IgD. They play different roles in immunity.
- Antibody production increases when exposed to an antigen to provide future protection against it. This is the basis of vaccination.
- Presence of antibodies in blood indicates current or prior exposure to an antigen. This is used for diagnostic testing.
- Each antibody responds to a single specific antigen epitope, unlike B and T cells which recognize multiple antigen parts.
In summary, antibodies are Y-shaped glycoproteins that bind antigens to tag, neutralize and eliminate pathogens, viruses, and toxic substances as part of the adaptive immune response.
How To Measure Antibody Titer?
Antibodies are proteins produced by plasma cells that recognize and attach to antigens on bacteria, viruses, or other foreign substances to mark them for destruction.
Titer tests measure the concentration of antigen-specific antibodies through:
- Binding With Antigens: Patient serum is mixed with antigen proteins. Higher antibody levels result in greater binding, visible through colour changes.
- Serial Dilutions: Serum is diluted to determine how far it can be diluted before antibodies become undetectable. The highest dilution that still binds antigen is the titer.
- Titer Levels: Results are reported as titers or ratios, such as 1:32. This reflects the maximum serum dilution level at which antibodies were detected via binding.
Higher titers indicate greater antibody levels and immunity. Lower titers suggest potential susceptibility.
Interpreting Antibody Titer Results
- No detectable titer: No measurable antibodies. No immunity against that disease.
- Low positive titer: Minor protection that may wane over time. Additional immunization is needed.
- High positive titer: Optimal antibody levels, indicating likely immunity. Low infection risk.
- Very high titer: May recommend recent exposure/active infection in some cases.
Each infection has an established titer considered adequately protective. Doctors assess results against this benchmark.
Why Test Antibody Titers?
Monitoring titers helps:
- Confirm immunity status for diseases like measles, rubella, and hepatitis B.
- Decide if immunization is needed in unvaccinated individuals.
- Check vaccine response in immunized people.
- Screen for suspected infection if symptoms present.
- Identify waning immunity that requires a booster shot.
- Monitor response to immunoglobulin therapy.
- Evaluate immunity in pregnant women to prevent fetal infection.
- Assess immune disorders causing abnormal titers.
Diseases Checked by Titer Testing
Some common titer tests include:
- Hepatitis B: Important for monitoring immunity after vaccination.
- Hepatitis A: Checks status if planning travel or potential exposure.
- Rubella: Screens pregnant women to prevent congenital rubella syndrome in infants.
- Measles: Low childhood vaccination rates make titers important to verify immunity.
- Mumps: Used on adults born when vaccination was less routine to check protection.
- Varicella zoster: Checks chickenpox/shingles immunity to guide vaccination needs.
- Epstein-Barr virus: Diagnoses mononucleosis infection, causing high titers during acute illness.
When Are Antibody Titer Tests Recommended?
Doctors may order titer tests if patients:
- Lack of vaccination records.
- Have received vaccinations over 10 years ago.
- Have a potential exposure risk through travel or work.
- Are pregnant.
- Are immunocompromised.
- Have received blood products or immunotherapy.
- Show symptoms of a specific infectious disease.
- Require screening for immunity disorders.
How Are Titer Tests Performed?
Antibody titer blood tests generally use one of these methods:
- ELISA: The enzyme-linked immunosorbent assay detects antibody-antigen binding through colour change reactions. Easy to automate for high volume.
- Agglutination: Serial dilutions of serum are mixed with antigen-coated particles. Higher titers cause visible clumping.
- Complement Fixation: Antibody binding activates complement proteins. Unbound complement hemolysis red blood cells, indicating lower titers.
- Neutralization: Patient sera are diluted and incubated with viruses. Less viral replication due to higher antibody neutralization indicates greater titers.
- Western Blot: Good for confirming specific antibody reactivity and ruling out non-specific interactions.
FAQs About Antibody Titer Testing
Antibody titer tests measure antigen-specific antibody levels in blood to evaluate immunity.
What is checked in an antibody titer test?
Titer tests measure the level or concentration of antibodies against a specific antigen or pathogen in the bloodstream as an indicator of immunity.
How are antibody titer results reported?
Titers are reported as dilutions such as 1:16 or 1:64. The higher the second number, the greater the antibody levels detected in the blood sample.
When would a doctor order titer testing?
To check immunity before/after vaccination, assess infection risk, screen pregnant women, diagnose illnesses with distinct titer patterns, or evaluate suspected immune disorders.
What does it mean if my titers are low?
Low titers indicate poor immunity against that disease antigen. Your doctor may recommend repeat vaccination or a booster immunization to increase protection.
What does a high titer mean?
High titers suggest good immunity due to prior infection or effective vaccination. Very high titers can occasionally signal current/recent active infection.
How To Prepare for an Antibody Titer Test?
Preparing correctly helps ensure accurate titer test results:
- Talk to your doctor: Discuss why the test was ordered and any special instructions.
- Note timing: Some titers require bleeding shortly after vaccination, when antibody levels peak.
- Provide vaccination history: Inform the doctor of any past immunizations relevant to titers being tested.
- Fast before testing: Fasting for 8–12 hours ensures clear results, unaltered by dietary lipids.
- Avoid hemolysis: Haemolyzed blood can falsely lower titers, so avoid strenuous exercise just before testing.
- Pause medicines: Hold off on certain medications that could potentially impact results.
- Consider age: Titers from different age groups may not correlate well, depending on prior exposures.
- Use the same lab: Compare results from the same laboratory over time for consistency.
With proper preparation, antibody titer testing provides an accurate assessment of your immune protection against specific infectious diseases.
Key Takeaways About Antibody Titer Testing
- Titer tests measure antigen-specific antibody levels, indicating immunity to diseases.
- Higher titers signal greater immunity, while lower titers suggest potential susceptibility.
- Checking titers guides decisions about vaccination needs and booster shots.
- Each infection has a defined protective titer level that doctors use to interpret results.
- Titers help diagnose some illnesses, screen pregnant women, and monitor vaccine response.
- ELISA, agglutination, neutralization and other immunoassays are used to detect titers.
- Proper sample timing, medication avoidance, consistent labs, and other preparation is key.
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