What are the allergy tests?
An allergy is a protective reaction of the human immune system to harmless substances, such as pollen, dust, or food. The more sensitive the immune system is to the allergen, the more severe the symptoms. Allergies can cause watery or red eyes, sneezing, runny nose, itching, or upset stomach.
Rarely, an allergic reaction can also cause anaphylaxis. This causes the airways to constrict, resulting in severe shortness of breath and a sharp drop in blood pressure. Without immediate treatment, such shock can be fatal.
To find out which substance triggers an allergic reaction, various tests can be performed: Skin tests, blood tests, and so-called irritation tests. A suitable allergy test can usually be found as a result of a group of symptoms and medical history in the doctor’s office.
What are skin tests?
Skin tests can be performed quickly and easily, which is why they are often on the first diagnosis line. In a skin test, possible allergens are applied to the skin and the reaction is monitored. This usually occurs on the underside of the forearm, sometimes on the back.
The prick test
The English word “prick” means “puncture”. Many have probably heard the term, after all, this allergy test is the most commonly used. But what exactly is a prick test? The term comes from the English verb “to prick”, which means “to pierce” and thus describes an important part of the execution.
During a skin examination, the physician examines various allergens or the patient’s reaction to them. In such a test, the doctor applies an aqueous solution containing an allergen such as pollen or traces of animal hair to marked areas of the skin. There, the skin is lightly scratched with a lancet to allow the allergens to penetrate.
This allergy test can detect immediate reactions, which is why it is useful to suspect so-called immediate allergies, i.e. physical reactions that start within a few minutes. There is a standard range for skin testing, which includes about 15-20 solutions with the most common allergens. Doctors always perform so-called positive and negative controls to better assess the results of other solutions.
The active control is a saline solution to which the patient should not react. When this is the case, the skin can generally overreact.
In the skin test, the negative control is histamine. An obvious reaction, such as nodulation, is not a sign of allergy but is desirable. These two solutions ensure that the results of the Sting test are evaluable, or more precisely, usable.
Importantly, sting tests can be used to identify allergies where the cause of a reaction occurs immediately after exposure – such as hay fever or certain food allergies.
The intradermal test
The effect of the intradermal test is similar to that of the skin test. This means that the affected person is exposed to the allergen.
The difference, however, is that the physician injects the allergen into the skin (intradermal injection) instead of just superficially applying it to the skin. Thus, this test can detect even weaker allergic reactions.
Such an allergy test is usually used only if the previous skin test did not provide suitable results. This is due to the fact that the injection is usually more irritating for those affected and the allergic reaction is correspondingly stronger.
Since this test is somewhat more uncomfortable, as the injections go directly under the skin and can also cause a stronger allergic reaction, it is only recommended if the prick test does not show a corresponding reaction.
If the results of the prick test are not clear enough, the scratch test can be used in addition to the intradermal test.
“Scratch” is the English word for “scratch” – and with this allergy test, the name says it all. The doctor scratches the surface of the skin (but does not make the specimen bleed) and rubs the suspected allergen onto the skin at this point. This friction allows the corresponding allergens to penetrate deeper into the tissue, which is why this allergy test is often taken as an option when a skin test does not yield results.
However, it is not possible with such a test to control the amount of allergens that actually enter the body. For this reason, and because this test is relatively insensitive, its validity is limited.
However, it is suitable for liquids and water-soluble substances, for example, for food or drug allergy tests. If the affected person reacts allergically, redness and swelling occur within about 20 minutes.
The friction test
The friction test is used when a severe allergic reaction is suspected. The test substance is rubbed onto the skin and the test is read after about 20 minutes. The scratch test is more sensitive compared to the rub test. The substance is applied to the skin and scratches the skin surface. Again, the allergic reaction sets in after about 20 minutes.
The patch test (patch or patch test)
For this allergy test, your doctor will put a patch with the test substance on your skin, so that the skin remains intact during this allergy test and does not need to be scratched.
With these patches, doctors can apply up to 4,000 potential allergens to the back or inside of the forearm – not all at once, of course. Usually, the doctor first examines the so-called standard series, i.e. the 27 substances named in the test series of the German Dermatological Society, which are most frequently allergenic.
After 20 minutes, the doctor first checks whether there is a reaction under the test patches. Two follow-up checks after 24 hours each confirm or deny the result. The patch will then be evaluated, i.e. your doctor will check whether and to what extent poplars, blisters, and other allergic reactions have formed under the patches.
Which allergens can be detected with this allergy test? Allergens that trigger so-called late-type reactions. In other words, if an allergy is suspected and symptoms do not appear until hours or days after contact with the allergen, a doctor usually performs a skin test.
Which substances are usually tested?
- Preservatives and fragrances
- Nickel or cobalt
The blood test
Your doctor can diagnose allergies with a blood test. This means that the doctor takes blood from the person concerned and sends it to a laboratory for examination. The staff then checks how many specific IgE antibodies are detectable there. The term IgE stands for “Immunoglobin E” and refers to proteins that the body produces in response to or to prevent allergies.
A blood test is an option if the individual has a skin condition that could interfere with the skin test or if the skin test is too burdensome, for example, due to other serious allergies. Food allergies can be detected by blood tests, but they also provide clues when allergies to pollen, dust mites, animal dander or medications are suspected.
Although a doctor must draw blood for this test, some people find it more comfortable than, say, a skin test because it does not expose the body to allergens.
However, blood tests can only determine the cause of an allergy, as the body produces specific antibodies depending on the allergen.
In contrast, conclusions about the severity and type of allergy symptoms cannot be drawn from an allergy test with blood tests. The cost of such a test varies, but is usually covered by health insurance.
The provocation test
This term refers to an allergy test in which the physician applies an allergen to the mucous membranes of the affected person, where the symptoms mainly manifest themselves. Stimulus tests may indicate allergy when other tests are inconclusive or inconclusive. And it is the only method that can also detect non-allergic hypersensitivity reactions (e.g., intolerances).
In this procedure, the physician applies a suspected allergen to the mucous membranes. This occurs either directly (e.g. on the nasal mucosa or conjunctiva) or by inhalation by the patient or – in the case of food or drug allergies – by ingestion (oral). Then you have to wait and see (under medical supervision!) if and how your body reacts.
Even if no acute allergy symptoms are noticeable immediately before provocation, a physician must be prepared for skin tests and especially irritation tests so that he can react quickly to possible severe allergic reactions.
What is to be observed in principle? Finding an allergen is a step-by-step process: after consultation with a doctor, a skin test is usually carried out first. Blood tests are used when skin testing is difficult or too risky. Also, some allergens are not available as ready-to-use solutions for skin testing. A provocation test only makes sense if a skin test or blood test does not provide a clear result.
A skin exam is also important to let your doctor know if you have a lung condition, skin condition, or heart problems. The same applies if you are taking medications that can affect skin reactions, such as the antibiotics amoxicillin or penicillin, or painkillers such as ASA or ibuprofen.
The doctor treating you decides which type of allergy test makes the most sense for you.
After the interview, the doctor will decide whether an allergy test will provide more information about the disease. Skin allergy tests such as prick test (standard test) and epicutaneous test (patch test) are often used, in which allergens are introduced into or onto the skin.
Blood tests give general indications of allergies or detect specific sensitizers – depending on the values tested. Among others, the following allergens can be tested in the blood:
Pollen. Draw. . Pesticides. Animal fur. Court. Addictive.
The costs for an allergy test are in the two to three digit euro range. They vary depending on the test method and provider. Statutory and private health insurance companies usually cover the costs in the case of a concrete suspicion.
There are a variety of allergies, including:
- Pollen from trees (known as hay fever)
- Grasses and cereals
- House dust
- Animals or animal hair
- and many more.