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.
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).
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