Interferences in specific IgE testing
The matrix on which the allergen is immobilised directly affects sensitivity, specificity, stability and the risk of interference.
It is not only the allergen that matters, but how it is presented
In specific IgE testing, what matters is not only which allergen is used, but also how it is presented to the detection system.
The matrix is the support on which the allergen is immobilised, and this support directly affects sensitivity, specificity, stability and the risk of interference.
The binding capacity of the solid phase
ImmunoCAP™ technology uses a three-dimensional matrix of activated cellulose sponge, with a far greater binding capacity than older systems such as passively coated tubes or activated paper discs.
This higher capacity matters because it allows the allergen to be available in a form closer to its natural state, and gives a better chance that the specific IgE in the patient’s serum will be captured, even when it is present at low concentrations. In practice, the cellulose matrix works like a very efficient sponge: it offers a large, stable and reproducible surface for immobilising the allergen.
Biotin interference
A major advantage of this technology is its analytical robustness. On some platforms, results can be affected by interferences such as biotin, particularly where the method relies on the biotin and streptavidin interaction.
ImmunoCAP™ does not depend on that principle in the same way, which reduces the risk that biotin supplements, frequently taken for hair, nails or skin, will lead to falsely low or otherwise altered results. Biotin interference is recognised particularly in immunoassays that use the biotin and streptavidin system.
CCD interference
Another important point is interference from CCD, cross-reactive carbohydrate determinants. These can sometimes produce positive results that do not necessarily reflect a clinically relevant allergy.
Here we must be accurate: CCDs can affect the interpretation of any IgE test, including under certain particular solid-phase conditions, and the literature describes rare situations in which patients with very high levels of anti-CCD IgE can show background reactivity.
The advantage of ImmunoCAP™ does not mean that clinical interpretation becomes unnecessary. It means the platform offers a well standardised, reproducible system supported by extensive clinical experience. Results must still be correlated with the patient’s history.
IgG and impurities in extracts
As regards IgG, the matrix and the assay design matter in limiting competition and non-specific binding. A patient’s serum contains many antibody classes, not only IgE. A good system must favour the specific detection of IgE and reduce the impact of antibodies that are not the target of the test.
The high binding capacity of the matrix helps present an excess of immobilised allergen, which supports the capture of specific IgE and contributes to a more stable measurement.
Impurities also deserve a mention. In allergen extracts, the quality of the biological material and the way it is immobilised are essential. A high-capacity matrix allows controlled binding of the relevant allergens and supports standardisation between lots.
The practical conclusion
Not all solid phases are equal. A matrix with a small surface can limit the amount of allergen available, reduce sensitivity and increase vulnerability to analytical variation. The three-dimensional cellulose matrix, by contrast, offers a large binding capacity, efficient allergen presentation and reproducible performance.
When we discuss ImmunoCAP™, we are not talking only about an IgE test, but about a technology in which the matrix is a key element: it contributes to sensitivity, precision, stability and to reducing the risk of relevant analytical interference. For the clinician, this translates into results that are easier to interpret, more consistent and more useful in medical decision-making.