Clinical & Interpretation

  1. How many components are there on ImmunoCAP ISAC?


  2. Can ISAC give information on allergens not present on the chip?

    Answer: Yes Example: A patient with suspicion of allergy is tested with extract-based tests and ISAC. ISAC is used to clarify the sensitization pattern. Result: The results confirm some allergen suspicions, but there is also a suspicion of allergy to e.g. melon, which is not presented on ISAC. Explanation: Even though specific components for melon are not present on ISAC, cross-reacting allergens originating from other sources than melon may be responsible for the melon sensitization. Some cross-reacting protein families like profilins, PR-10 proteins, CCD and LTPs are usually well conserved across species and may be markers also for allergens present in melon. The relevant component for the patient in focus is probably not present on the ISAC chip if explanation a) is not valid and no other ISAC components are identified. In this case it is recommended to complement with the ImmunoCAP extract-based test for e.g. melon. ISAC will never cover all allergens and therefore it is important to have knowledge regarding which allergens ISAC cover and also to what extent, i.e. if a major part of melon sensitized patients are identified with ISAC (like for peanut) or only a minor part (like for cashew) for a specific patient population.

  3. Why are my SPT and ISAC results not in agreement?

    Answer: Either the component is not present on ISAC, the extract-based test is contaminated with other components or ISAC is less sensitive in the low-level IgE concentration range. Example: A patient with allergy suspicion to e.g. dog has been tested with SPT and ISAC. Results: Positive SPT test for dog and mite. Mite, but not dog, is identified by ISAC. Possible scenarios: a) The patient may be sensitized to dog allergens not present on ISAC. b) The dog SPT test may be contaminated. For example, some dog extracts have been reported to be contaminated with mite allergens, which would then explain the sensitization to mite and dog on SPT, without any dog-specific molecules registered on ISAC. c) Low-level responses close to the limit of detection (< 1 ISU) may differ due to differences in the measurement techniques (see also answer 9 and 10).

  4. Why are the ImmunoCAP components and ISAC results not in agreement?

    Answer: The two methods are based on two different measurement techniques and this may cause discrepancies for some patient samples. Example: E.g. a peanut sensitized patient would like more information regarding the probability of having a severe reaction to peanut. Molecular testing is performed with the ImmunoCAP and ISAC technologies. Results: ImmunoCAP Ara h 2 = 4 kU/l, ISAC Ara h 2 < 0.1 ISU Explanation: Overall similar IgE ab levels are detected with the two technologies for most serum samples [1,2] but discrepant results may occur for individual samples or components. The two technologies differ in binding capacity and detection method; hence the results obtained from the two platforms will differ also theoretically. ImmunoCAP is a well-established, quantitative technology, while ISAC is a novel methodology and has to be regarded as semi-quantitative. Usually a somewhat higher IgE ab concentration is registered with the ImmunoCAP as compared with the ISAC technology.

  5. Can I trust low-level responses on ISAC?

    Answer: Yes, but most low-level result are not associated with clinical symptoms. Example: A patient with allergy suspicion is tested on ISAC. Results: Low-level responses (< 1 ISU) is registered. It has been reported that the CV for IgE levels < 1 ISU are high. Can I rely on these low-level results? Explanation: It has been reported that many low-level results are not associated with clinical symptoms. This may be due to the fact that clinical reaction do not occur until the allergen threshold for clinical symptoms have not been reached for the patient. The allergen load threshold can also be “pushed down” if the patient has an infection, is stressed or exposed to many allergens. The binding capacity on the glass chip is much lower than for the ImmunoCAP allergen components. All results, and especially low-level results, must be evaluated with extra attention taken to the clinical history. For low-level results (<1 ISU) the CV for ISAC increases significantly. Low-level results should therefore be evaluated with this in mind. Note also that protein families with very high sequence homology may be used for quality control. Usually the IgE ab level within the entire profilin family, within the entire tropomyosin family, and within most serum albumins are similar. A single low-level profilin/tropomyosin/serum albumin response could be due to background noise and should thus most likely be ignored.

  6. The ISAC chip contains too many components from irrelevant sources for my patient? Why should I order ISAC in this case?

    Answer: Results for other related components may also give useful information. Example: For my patient some allergens on the ISAC-chip are irrelevant (e.g. birch pollen), while others relevant allergen, e.g. strawberry are not represented on ISAC. Results: IgE abs to several allergens that belong to the PR-10 family are identified (birch Bet v 1 = 3 ISU, apple Mal d 1 = 7 ISU, kiwi Act d 8 = 45 ISU). How do I interpret these results given that birch pollen allergy is irrelevant for my patient? Explanation: Even though specific markers for some allergens like strawberry may not be present on ISAC, cross-reacting allergens (such as profilins, PR-10 proteins, CCD or LTPs) originating from other sources may also be markers for strawberry. The IgE sensitizations have to come from some source, the primary/dominating allergen. It is often useful to study the entire IgE pattern to elucidate the original sensitizer “driving” the IgE pattern for closely related allergens. For example, strawberries contain components that belong to the PR-10 protein family, and in the above example the PR-10 proteins in strawberry may cause the clinical reactions to strawberry. The IgE levels also give useful information regarding the original/dominating sensitizer. In this example the PR-10 response is probably not birch pollen driven (only 3 ISU), instead kiwi (45 ISU) or strawberry may be the original sensitizer.

  7. I am only interested in peanut, egg and milk, but not latex. Why are all the >100 results reported to me?

    Answer: ISAC can reveal unexpected allergens. In most cases only the relevant allergens are identified. In a minority of cases, unsuspected and relevant allergens are identified with ISAC, which is one of the strengths of the assay. However, in a minority of cases asymptomatic allergens are also identified, and it is often difficult to find out if this result is due to: - A true IgE ab response with lack of clinical symptoms due to an “allergen load” below the clinical threshold. The question is whether this IgE response will increase and lead to the development of clinical reactions, or decrease/stay stable and never give rise to any clinical reactions? - A true IgE ab response, with lack of clinical symptoms, due to a component that is rarely associated with clinical symptoms (such as CCD or profilin). - Assay artefacts giving rise to a false positive response. This can be assessed by checking low-level results with extra care, looking for other closely related allergens that may support your suspicion. Since the ISAC platform only supports one standard platform for all customers, IgE determinations to identical allergen panels are collected from different geographical regions and patient types. This facilitates valuable global/local analyses of IgE profile differences and similarities. It will also enable a robust research tool in the MA field and facilitate faster standardization of the clinical relevance and utility of different components. Since ISAC is a novel technique we believe it is of value for the entire MA field to collect as much information as possible in this early phase.

  8. How can I use the IgE ISU level information?

    Answer: It may hold information regarding the primary/dominating sensitizing allergen. Example: A grass pollen allergic patient is tested on ISAC. Results: Bermuda grass Cyn d 1 = 78 ISU and Timothy grass Phl p 1 = 6 ISU. Explanation: ISAC is a semi-quantitative technology, providing useful ISAC ISU levels. The relative ISU levels provide strong indicators and ISAC gives similar IgE ab levels as detected by the ImmunoCAP technology [1]. The ISU (ISAC Standard Units) are also calibrated against the ImmunoCAP kU/l in the measurement range 0.3 – 100 ISU. For patients with many IgE responses within the same/similar protein family, the response level indicates the original/dominating sensitizer. In this example Bermuda grass is likely the original sensitizer while Phl p 1 gives an IgE response due to cross-reactivity. Another example on the same topic: Background: A patient with suspicion of peanut and tree nut allergy is tested on ISAC. Results: Hazelnut Cor a 9 = 76 ISU, peanut Ara h 2 = 0.7 ISU, Ara h 3 = 1.6 ISU and soy Gly m 6 = 18 ISU. Explanation: In this example hazelnut is likely the original sensitizer, giving rise to cross-reactivity to both soy and peanut (with or without clinical manifestation).

  9. What type of patients is ISAC testing indicated for?

    Answer: ISAC is especially useful for multi-sensitized and problematic patients. A multi-sensitized or problematic patient can, for example, be patients with the following characteristics: - OAS and multi pollen & plant food sensitizations - asthma (most asthmatic patients referred to an allergy specialist are multi-sensitized) - atopic dermatitis (these patients often have very high total IgE and one of the advantages with ISAC is no interference of high total IgE responses) - idiopathic anaphylaxis - no/unsatisfying response to treatment - limited blood sample volume (ISAC only requires 30 ul sample) - not applicable SPT due to skin problems/young children ImmunoCAP ISAC can also: - reveal unexpected sensitizations - help identify risk-markers

  10. When is ISAC testing not indicated?

    For uncomplicated patient cases - where the clinical history is simple and clear - ISAC will probably not offer additional information. (This kind of patient is typically mono-sensitized with one or a few specific clinical questions (e.g. is it peanut allergy?).

  11. I want to perform Molecular testing: how do I know which method to choose, ImmunoCAP ISAC or ImmunoCAP components?

    Answer: It depends on the patient’s symptoms, anamnesis and case history. Choose ImmunoCAP components: - when you need a quantitative results with high accuracy, e.g. when following a patient over time to investigate an increased or decreased IgE ab level. - when you have one or a few specific clinical questions, e.g. is it egg allergy? Choose ImmunoCAP ISAC: - when you have a complex, multi-sensitized patient - when you have many clinical questions or when you have difficulties to formulate the questions due to an unclear patient history - when you have a limited blood sample volume.

  12. Where do I find information about what components are present on the ISAC chip and their characteristics?

    The components that are present on the ISAC chip are all listed in the ImmunoCAP® Cross-Reactivity Map, which is available for download if you navigate to Dianet --> Molecular Allergology --> ImmunoCAP ISAC --> Marketing material. Additional information on the new components included in the ISAC 112 is also available in “New Components and the rationale behind“. ( Dianet --> Molecular Allergology --> ImmunoCAP ISAC --> Marketing material)

  13. Is the component native or recombinant?

    Also this information is present in the ImmunoCAP Cross-Reactivity Map, please see attached below or go to Dianet. (Dianet --> Molecular Allergology --> ImmunoCAP ISAC --> Marketing material). Components marked with r, are recombinant and those marked with n are native. This information is also present in the MIA software as soon as the customers start to run and analyze their samples.

    Related document:

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.