Comparative research between results of skin prick tests and prick to prick tests performed with fruit and vegetable extracts.

Homemade extracts of foods have been made in the Erasmus Medical Center for
some time now (mid-nineties), which are used in the diagnosis of an
IgE-mediated food allergy. The skin tests performed with these extracts are a
fast, reliable and cheap method to confirm sensitization in the patient. Over
the years, less food allergens have been commercially available, and are
usually not registered. The specificity and sensitivity of the allergens that
are still available is usually unknown. As Department of Allergology, we are
highly dependent on the homemade extracts when diagnosing a suspected food
allergy. For the food allergen extracts that are used, finding the most
reliable way of performing the skin test (as a skin prick test with homemade
extract, or as a prick-prick test with the fresh food) is of great importance.

1. Are the results of the skin prick test (SPT) performed with homemade
extracts and the prick-to-prick test (PTP) with fruit and vegetables comparable?
2. Is there a difference in sensitivity and/or specificity between the SPT and
PTP with fruit and vegetables, compared to specific food allergic complaints
answered in the questionnaire?
3. Is there a difference in SPT and PTP test results compared to measured serum
IgE levels in the patient's blood?

During performing the skin tests, 2 methods are compared in participants of the
study; the skin prick test (SPT) with homemade extracts of fruit and vegetables
and the prick to prick (PTP) with fresh fruit and vegetables. We test 5
allergens, namely apple, kiwi, peach, tomato and carrot, in the same patient.
The skin tests are performed on the forearm, the reactions are measured and
scanned after 15 minutes. The HEP (histamine equivalent prick test) index is
used. The questionnaire regarding food-related complaints after eating apple,
kiwi, peach, tomato and carrot is completed.
A tube of blood (8 ml) is taken from the patient to determine the
allergen-specific serum IgE.

After assessment of the health question in the referral letter, the patient
will receive the information letter about the study, together with the
invitation for the first visit to the allergist. The patient will be given
enough time to consider taking part in the study. During the first visit to the
allergist, the patient will have the opportunity to ask questions, and will be
asked to participate in the study.
The visit will take approximately 1 hour. 5 food allergens will be double
tested when participating; as skin prick test (SPT) with homemade food
allergens, and prick to prick test (PTP) with fresh food. We will test apple,
kiwi, peach, tomato and carrot.
As a result of the skin test, a little red itchy bump may develop at the site
of the test, the forearm, which is at its worst after 15 minutes and then
disappears spontaneously. If the patient experiences too much itching, in
consultation with the allergist, an antihistamine can be given. A questionnaire
about the diet-specific history will be completed, which will take
approximately 10 minutes. A tube of blood (8 ml) will be collected by means of
a venipuncture. After collecting blood, a bruise may occur, which will
disappear spontaneously within 1 week.