When diagnosing an allergy, HISTORY is the most important factor (DynaMed Plus, 2018)!
This means lots of questions and information about what you've eaten, activities you've done, if you've had any reactions before, or what happened when you did!
It's important to answer these questions as completely as possible, the nurse doesn't want to judge you, just to understand how they can best help.
There are some tests that get performed to diagnose allergies too:
Skin tests:
There are 2 kinds of skin tests, both involve using extracts of common or suspected allergens to observe for a 'wheal and flare' reaction, which is a raised area on the skin with redness surrounding it (Goodridge, Lewis, Goldsworthy, & Barry, 2014).
Allergy tests can be done to check for allergies to penicillin, animals, latex, some foods, and some medications. Skin tests cannot be done for several weeks after an allergic reaction to avoid confounding results (Goodridge, Lewis, Goldsworthy, & Barry, 2014).
Usually, on your arm or back, your health professional will map out which allergens they are testing, and make a second row to test with saline as a control (to make sure your skin isn't just reacting to the poke)(Goodridge, Lewis, Goldsworthy, & Barry, 2014).
For PERCUTANEOUS or SKIN PRICK tests, the solution is applied to the skin and then a sharp instrument pricks the skin through it introducing it into the top layers of skin (Goodridge, Lewis, Goldsworthy, & Barry, 2014).
For INTRADERMAL or INTRACUTANEOUS tests, the solution is injected under the skin. This one is typically contraindicated for food allergies (Goodridge, Lewis, Goldsworthy, & Barry, 2014). It has a chance of reading false positives, or triggering a severe reaction like anaphylaxis itself (Goodridge, Lewis, Goldsworthy, & Barry, 2014).
After exposure, you will not be left alone in case of allergic reaction. They may trigger allergic responses as you are actually being exposed to the allergens (Goodridge, Lewis, Goldsworthy, & Barry, 2014). The areas tested will be observed for the characteristic wheal and flare. The size of the wheal and flare DOES NOT always correlate with severity of the allergy(Goodridge, Lewis, Goldsworthy, & Barry, 2014)!
Skin tests are harder to read on dark skinned individuals.
Blood tests:
If skin tests have been ruled dangerous, or if you've had a severe reaction previously, a blood test may be recommended (Goodridge, Lewis, Goldsworthy, & Barry, 2014).
Blood tests are recommended for food allergies, medications, insect bites and stings, and vaccines (which are a very rare allergy)(Goodridge, Lewis, Goldsworthy, & Barry, 2014).
The blood sample is analyzed for specific IgE's are in your blood, and shows what your body might be sensitized to(Goodridge, Lewis, Goldsworthy, & Barry, 2014).
With all tests, false negatives and positives can occur. A reaction indicates that you are sensitized to an allergen but may not definitively show that this is what caused the initial reaction(Goodridge, Lewis, Goldsworthy, & Barry, 2014). This is why history is so important as well! Together the tests and history may provide a better picture of what your body is reacting to(DynaMed Plus, 2018; Goodridge, Lewis, Goldsworthy, & Barry, 2014).
Blood tests may also be done during an anaphylactic emergency. At this point they will be analyzing blood for different chemicals which indicate the presence of an allergic response (DynaMed Plus 2018).
Serum Tryptase:
This is related to a drop in blood pressure (specifically in your arteries). This peaks about 1-2 hours after onset. The comparison from baseline (as soon as you arrive) to 1-2 hours later is the important factor, as amounts of tryptase vary between humans anyway (Laroche, Gomis, Gallimidi, Malinovsky, & Mertes, 2014).
Plasma Histamine:
This is a more immediate indicator, as histamines are strongly linked with the allergic process and a high level of histamines is indicative of allergic response (Laroche, Gomis, Gallimidi, Malinovsky, & Mertes, 2014).
These tests may be done as soon as you arrive as a baseline, as there is no definitive value that marks an allergy. Both tests are measured relative to an individual's normal levels (Laroche, Gomis, Gallimidi, Malinovsky, & Mertes, 2014).
References:
DynaMed Plus. (2018, Nov 30). Anaphylaxis. Ipswich, MA: EBSCO Information Services. Retrieved May 4, 2019, from http://www.dynamed.com/login.aspx?direct=true&site=DynaMed&id=113862
Goodridge, D., Lewis, S. M., Goldsworthy, S., & Barry, M. (2014). Medical-Surgical Nursing in Canada: Assessment and Management of Clinical Problems (3rd Canadian ed.). Toronto, ON: Elsevier Canada
Laroche, D., Gomis, P., Gallimidi, E., Malinovsky, J., & Mertes, P. M. (2014). Diagnostic value of histamine and tryptase concentrations in severe anaphylaxis with shock or cardiac arrest during anesthesia. Anesthesiology, 121(2), 272-279. doi:10.1097/ALN.0000000000000276
DynaMed Plus. (2018, Nov 30). Anaphylaxis. Ipswich, MA: EBSCO Information Services. Retrieved May 4, 2019, from http://www.dynamed.com/login.aspx?direct=true&site=DynaMed&id=113862
Goodridge, D., Lewis, S. M., Goldsworthy, S., & Barry, M. (2014). Medical-Surgical Nursing in Canada: Assessment and Management of Clinical Problems (3rd Canadian ed.). Toronto, ON: Elsevier Canada
Laroche, D., Gomis, P., Gallimidi, E., Malinovsky, J., & Mertes, P. M. (2014). Diagnostic value of histamine and tryptase concentrations in severe anaphylaxis with shock or cardiac arrest during anesthesia. Anesthesiology, 121(2), 272-279. doi:10.1097/ALN.0000000000000276