Various methods are used to diagnose food allergy:
- Prick test (detection of type 1 allergies) – a drop of an allergen extract is applied to the patient’s skin and then a lancet is used to prick the skin about 1 mm; the result is then read after about 10 minutes
- Scratch test – here, allergen extracts are also applied to the patient’s skin, which is then scratched superficially for a few millimeters with a lancet
- Rub test (rubbing in the allergen) – the presumed allergen is rubbed on the inside of the forearm; in the case of positive failure shows after a few minutes an erythema (areal skin redness) or wheals
- Intracutaneous test (detection of type 1 allergies) – similar to the prick test, but more sensitive! In this test, a defined amount of an allergen extract is injected intracutaneously and also read after 20 minutes against a blank test.Cave! There is a risk of a high-grade allergic reaction with this test.[Ready allergen solutions for intradermal testing are probably no longer available in Germany].
Note: “Only with a suitable medical history and/or positive food provocation, the diagnosis of a food allergy (NMA) can be derived from the skin tests. In contrast, a lack of sensitization usually excludes IgE-mediated NMA.”
1st order laboratory parameters – obligatory laboratory tests
- RAST (radioallergo-sorbent test) – measurement of allergen-specific IgE antibodies (single allergens) in serum; preferred in infants and young children [leads to tentative diagnosis].
- EAST (enzyme allergo-sorbent test).
Meat allergy diagnostics
If alpha-Gal-mediated meat allergy is suspected: test for total extract (beef, pork and lamb) and allergen component (alpha-Gal). Galactose-alpha-1-3-galactose (alpha-Gal) is a disaccharide found in the meat of beef, pork, lamb, and venison (muscle meat and offal) or their cells.Onset of an anaphylactic reaction approximately 4 to 6 hours after contact with the allergen.Sensitization to alpha-Gal is thought to occur primarily via ticks; thus, a history of a tick bite supports the diagnosis of alpha-gal syndrome.
Food provocation to confirm a suspected diagnosis
Procedure: Elimination diet for a maximum of two weeksIf symptoms improve: oral provocation – ideally double-blind and placebo-controlled [= gold standard in the diagnosis of IgE-mediated NMA]Note: Higher age and previously experienced anaphylactic reactions to the suspected food are considered confirmed risk factors for an anaphylactic reaction in the context of oral food challenge (“OFC”). According to one study, an elevated level of sIgE (specific IgE) to food allergens is thought to be an important predictor of an anaphylactic reaction in an overt food challenge.