As you have understood, it is not that simple with analyzes.
Each analysis has several characteristics:
- sensitivity – the percentage of coincidence of the positive result with the allergy detected (including false-negative results);
- pecificity – the percentage of coincidence of the negative result with the absence of allergy;
- a positive prognostic value – the ratio of cases of allergies to all positive test results;
- a negative prognostic value – the ratio of cases of lack of allergy to all negative test results.
Why are there so many difficulties?
You need to understand that not one laboratory test has 100% sensitivity and specificity, and a 100% predictive value. There are tests with high listed indicators, and they are included in the diagnostic protocols.
“That’s why an elevated level of eosinophils does not always mean an allergy, and a normal level of total IgE does not guarantee its absence. There are too many reasons for increasing the number of eosinophils, and the prognostic value is low for the general IgE.
Therefore, neither analysis is used for screening for allergic disease.
Our “favorite” specific IgE and skin tests are most interesting. Their sensitivity and specificity are high enough, therefore they are included in the gold standard of allergy tests. And yet, in about 10-15% of cases, they can be positive in people with no allergy. This condition is called asymptomatic sensitization.
Asymptomatic sensitization can lead to allergies in the future and can be completely neutralized. It occurs at any age.
Identifying specific IgE in the blood or using skin tests is not the equivalent of an allergy, because it always requires comparing the results with the symptoms.
That is why any expert analysis for allergens should be accompanied by a consultation of a competent specialist.