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Titre - Titer
🔬 The titer (titre, UK spelling) corresponds to the highest dilution factor of a sample that still yields a positive result. It is a way of estimating the concentration of an analyte such as antibodies in serum.
📖 About
- The titer reflects the concentration of a substance, determined by the highest dilution at which it still exerts a measurable effect.
- Example (antibodies): The titer is the highest dilution of serum at which antibodies still cause visible agglutination with antigen.
- Thus, a higher titer (i.e., positive result at high dilution) indicates a greater concentration of the molecule being tested.
- Titers are widely used in immunology, microbiology, and infectious disease diagnostics to quantify immune responses.
🧬 Clinical Example: Antinuclear Antibodies (ANA)
- Threshold: Positive ANA titres at dilutions ≥ 1:160 are generally considered clinically significant.
- Low titres: Positive titres <1:160 are found in up to 20% of healthy individuals, especially older adults.
- High titres: ANA ≥1:160 are strongly associated with autoimmune diseases (e.g., SLE, Sjögren’s, systemic sclerosis).
- However, even high titres can occasionally be present in ~5% of healthy people, so clinical context is essential.
💡 Key Points
- Reported as a ratio (e.g., 1:40, 1:160, 1:640) → higher denominator = stronger antibody concentration.
- Not diagnostic alone: titres must be interpreted alongside clinical features and other tests.
- Useful for monitoring disease activity and immune responses over time.
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