The ImmunoCAP Immuno‑Solid phase Allergy Chip (ISAC) is a CE‑marked molecular diagnostic test that can test for IgE antibodies to 112 components from 51 allergen sources at the same time. It is a miniaturised immunoassay platform that uses a single sample (30 microlitres) of serum, plasma or capillary blood.
Each slide contains 4 microarrays giving results for 4 samples per slide. ImmunoCAP ISAC is a 2‑step assay. IgE antibodies from the patient sample bind to immobilised allergen components spotted in triplets on polymer‑coated slides. An enzyme‑labelled antibody detects the IgE‑allergen complex. The results are measured using a biochip scanner. Confocal laser scanning devices, in particular the CapitalBio LuxScan 10K microarray scanner, are recommended. The results are evaluated using the proprietary Microarray Image Analysis software, which, like the ImmunoCAP ISAC, is also produced by Phadia.
ImmunoCAP ISAC is a semi‑quantitative test and results are reported in ISAC standard units (ISU) indicating specific IgE‑antibody levels; the operating range is 0.3–100 ISU‑E. This range is about the same as a concentration range of 0.3–100 kilo international units of allergen‑specific antibody per unit volume of sample (kUA/litre) of IgE (1 kUA/litre is equal to 2.4 nanograms/ml). The assay takes 4 hours to give a result, including sample processing and incubation time.
Microtest is a CE‑marked, in vitro diagnostic test, which uses microarray technology to measure specific antibodies to 22 allergen extracts and 4 allergen components at the same time. It is a miniaturised immunoassay platform and uses a single sample (100 microlitres) of serum or plasma. IgE antibodies from the patient sample bind to immobilised allergen extracts and components spotted on the Microtest biochip.
Each slide contains 1 matrix microarray. Up to 5 microarrays can be assayed at the same time on the platform. Microtest is semi‑automated and includes a 3‑step reaction. The sample is incubated on the slide, during which time the IgE antibodies from the sample bind to the immobilised allergens. An enzyme‑labelled antibody detects the IgE‑allergen complex and a detection solution is used to develop the fluorescence. Once the chips have been washed and dried, the platform automatically reads and analyses the signal. The fluorescent signal is processed using the Microtest software. The Microtest platform can process up to 5 samples in each run.
Microtest is a semi‑quantitative test and results are calculated in kU/litre (kilo international units of allergen specific antibody per unit volume of sample) and reported in IgE classes (class 0: <0.35 kU/litre; class 1: 0.35–1 kU/litre; class 2: 1.01–15 kU/litre; class 3: >15 kU/litre) giving specific‑IgE‑antibody levels. The operating range is 0.3–100 kU/litre; 1 kU/litre is equal to 2.4 nanograms/ml. The Microtest procedure is reported to take about 4 hours to give a result.
The comparator for this assessment was current standard clinical assessment, which should always include an allergy‑focused clinical history and can additionally involve single specific‑IgE testing, skin prick testing, oral‑food‑challenge testing or a combination of these approaches.