Although skin testing in allergy normal involves prick (scratch) and intradermal methods for evaluation of immunological status. The intradermal skin test includes both immediate (seconds and minutes) in order to assess an allergic status (IgE- mast Cell) while it can also be used to assess cell mediated function that is measured in 24-72 hours.
However, another form of intradermal allergy skin testing that is controversial is the skin end point titration (SET) that uses intradermal injection of allergens at increasing concentrations to measure allergic response. The test is performed using progressive dilutions of allergens and after 10 minutes, the injection site is measured to look for growth of wheal. If there is more than 2 millimeters of growth in 10 minutes then the SET is considered positive. And then a second injection at a higher concentration is given to confirm the response. The end point is the concentration of antigen that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal grows larger than 13 mm, then no further injection are given since this is considered a major reaction.
Serial end-point titration (SET) testing ”studies” were actually empiric observations of individual reports and published as only case reports. There were no controlled objective assessments to support a specific claim for safety and efficacy (effectiveness in the real world). A critical
fault of this method is the lack of attention to the presence of erythema at the test site which would have been a prerequisite for
a specific diagnostic test of allergies in these diseases. Wheal diameter with accompanying erythema is an efficient indication of the degree of skin test reactivity to an allergen, but clearly if there was no erythema then it is likely to lead to clinically false-positive test results.
Thus the technique of skin testing by intradermal SET using the method of Rinkel is not recommended as a reliable test for IgE-mediated skin sensitivity due to
1: because the tests are prematurely read during the course of the reaction, and the presence or absence of accompanying erythema is not considered;
2: the method clearly would generate additional and unnecessary intradermal injections;
3: the use of the ‘endpoint’ as the dose for initiating immunotherapy frequently unnecessarily prolongs the course of treatment;
4: the ‘optimal’ dose of immunotherapy that is calculated is arbitrarily created;
5: and controlled studies show that it results in ineffective treatment.