Titre

Titre (or Titer) is a term used in immunology and microbiology to describe the concentration of a substance in a solution, typically referring to the concentration of antibodies or antigens in the blood. The titre is determined by performing a series of dilutions and is expressed as the inverse of the greatest dilution that still gives a positive result.

Overview

In medical and scientific contexts, the titre is a crucial measurement used to assess the strength of an immune response or the presence of a particular substance. It is commonly used in serology to determine the concentration of antibodies in a patient's serum, which can indicate past or present infection, immunity, or exposure to a particular pathogen.

Measurement

The process of determining a titre involves serial dilution of a sample, such as blood serum, and testing each dilution for the presence of the target substance. The highest dilution that still produces a detectable reaction is considered the titre. For example, if a serum sample is diluted 1:256 and still shows a positive reaction, but a 1:512 dilution does not, the titre is said to be 1:256.

Applications

In Immunology

In immunology, titres are used to measure the concentration of antibodies against specific antigens. This is important for:

• Diagnosing infections: High titres of specific antibodies can indicate an active or recent infection.
• Determining immunity: Titres can assess whether a person has immunity to a disease, either from vaccination or previous infection.
• Monitoring autoimmune diseases: In conditions like lupus or rheumatoid arthritis, titres of autoantibodies can be used to monitor disease activity.

In Microbiology

In microbiology, titres can refer to the concentration of viruses or bacteria in a sample. This is important for:

• Quantifying viral load: In diseases like HIV or hepatitis, viral titres can help assess the severity of infection and response to treatment.
• Vaccine development: Determining the concentration of virus needed to elicit an immune response is crucial in vaccine research.

Interpretation

The interpretation of a titre depends on the context and the specific test being used. A high titre may indicate a strong immune response, while a low titre might suggest a weak or absent response. However, the clinical significance of a titre must be considered alongside other clinical findings and diagnostic tests.

Limitations

While titres provide valuable information, they have limitations:

• Variability: Different laboratories may use different methods, leading to variability in results.
• Cross-reactivity: Antibodies may react with similar antigens, leading to false positives.
• Timing: The timing of sample collection can affect titres, as antibody levels change over time.

Also see

• Antibody
• Antigen
• Serology
• Dilution
• Immunoassay