Tests
1st tests to order
serum tryptase level
Test
Serum samples should be taken as soon as possible after emergency treatment has started, with a second sample ideally within 1 to 2 hours (but no later than 4 hours) from the onset of symptoms.[54]
Serum tryptase levels are normally undetectable (<1 nanogram/mL) in healthy individuals who have not had anaphylaxis in the preceding hours. In anaphylaxis, elevations can range from insignificantly elevated to levels above 100 nanograms/mL.
Elevation of tryptase levels may also exist in nonanaphylactic conditions, such as systemic mastocytosis.
Available in all major labs (e.g., as ImmunoCAP), and can be measured postmortem.
To determine the baseline level of tryptase, an additional sample should be collected at least 24 hours after all symptoms have resolved.
Not necessary when diagnosis of anaphylaxis is definite.
In clinically obvious food-induced anaphylaxis, tryptase levels may not be elevated, even if serum was collected in a timely manner.[56][57]
Result
elevated
Tests to consider
in vitro IgE testing
Test
An in vitro quantitative assay measuring allergen-specific IgE in human serum.
Provides a clinically relevant means of confirming or excluding the presence of atopy. Also accurately identifies specific allergen sensitivities in patients with confirmed allergy. Unfortunately, an abnormal value does not imply clinical reaction or indicate the severity.[66]
For food allergy, sensitivity is 86% and specificity 83%.[67]
Result
>0.35 international units/L
skin test
Test
Three main types are: the scratch test, also called puncture or prick test; the intradermal test; and the patch test.[68][69]
A variety of allergen extracts for skin testing are commercially available. Skin testing with commercial extracts, or fresh fruit, has a high sensitivity and a negative predictive value of >90%.[61]
Few extracts are available to test for drug allergy.
Result
>3 mm diameter and greater than control
challenge test
Test
The patient is challenged with increasing amounts of the offending allergen. This is the best method to confirm a diagnosis of allergy; however, a challenge test should be avoided in patients with a history of anaphylaxis because of the associated risk.[70] If a causative food has not been identified but food allergy is suspected, a food challenge might be necessary as the specific food avoidance might be life-saving.
Result
objective symptoms of allergy response
Emerging tests
basophil activation test
Test
Flow-cytometry test assessing reaction of basophils to allergens. Has been described as a supplemental tool in diagnosing severe peanut allergy in adults.[62]
Result
basophil activation
Use of this content is subject to our disclaimer