An allergy is a protective reaction of the human immune system to substances that are actually harmless, such as pollen, dust or food. The more sensitive the immune system is to the allergen, the more severe the symptoms are. Allergies can cause watery or red eyes, sneezing, a runny nose, itching or an upset stomach.
Rarely, an allergic reaction can also cause anaphylaxis. This causes the airways to narrow, leading to severe shortness of breath and a sharp drop in blood pressure. Without immediate treatment, this type of shock can be fatal.
To find out which substance triggers an allergic reaction, various tests can be carried out: skin tests, blood tests and so-called irritation tests. A suitable allergy test can usually be found in the doctor's office as a result of a description of symptoms and anamnesis.
What are skin tests?
Skin tests are quick and easy to perform, which is why they are often the first line of diagnosis. A skin test involves applying possible allergens to the skin and monitoring the reaction. This usually occurs on the underside of the forearm, sometimes on the back.
The prick test
The English word "prick" means "puncture". Many people have probably heard the term, after all, this is the most commonly used allergy test. 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 procedure.
During a skin examination, the doctor 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. The skin is then lightly scratched with a lancet so that the allergens can penetrate.
This allergy test can detect immediate reactions, which is why it makes sense to suspect so-called immediate allergies, i.e. physical reactions that occur within a few minutes. There is a standard range of skin tests that includes around 15-20 solutions with the most common allergens. Doctors always carry out so-called positive and negative controls in order to be able to better assess the results of other solutions.
The active control is a saline solution to which the patient should not react. If they do, the skin in general may overreact.
In the skin test, the negative control is histamine. An obvious reaction, such as the formation of nodules, is not a sign of an allergy, but is desirable. These two solutions ensure that the results of the sting test can be evaluated, or more precisely, used.
Importantly, prick tests can be used to detect allergies where the cause of a reaction occurs immediately after exposure – such as hay fever or certain food allergies.
The intracutaneous test
The effect of the intracutaneous 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 doctor injects the allergen into the skin (intradermal injection) rather than just putting it on the skin superficially. This means that this test can also detect milder allergic reactions.
Such an allergy test is usually only used if the previous skin test did not produce suitable results. This is because the injection is usually more irritating for those affected and the allergic reaction is correspondingly more severe.
Since this test is a bit more uncomfortable because 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 any corresponding reaction.
scratch test
If the results of the prick test are not clear enough, the scratch test can be used in addition to the intracutaneous 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 cause the sample to 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 used as an option when a skin test does not produce any results.
However, it is not possible to control the amount of allergens that actually enter the body with such a test. For this reason and because this test is relatively insensitive, its significance is limited.
However, it is suitable for liquids and water-soluble substances, for example for food or drug allergy tests. If the affected person has an allergic reaction, redness and swelling will occur within about 20 minutes.
The patch test (patch or plaster test)
During this allergy test, your doctor will stick a patch containing the test substance onto 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 the inside of the forearm - not all at once, of course. The doctor usually first examines the so-called standard series, i.e. the 27 substances named in the test series of the German Dermatological Society that most frequently trigger allergies.
After 20 minutes, the doctor will first check whether there is a reaction under the test patches. Two follow-up tests after 24 hours each confirm or deny the result. The patch is then 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 cause so-called delayed-type reactions. In other words, if an allergy is suspected and symptoms only appear hours or days after contact with the allergen, a doctor will usually perform a skin test.
Which substances are usually tested?
- preservatives and fragrances
- nickel or cobalt
- latex
- drug
The rubbing test
The rub 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 than the rub test. The substance is applied to the skin and the skin surface is scratched. Here too, the allergic reaction sets in after about 20 minutes.
The blood test
Your doctor can diagnose allergies with a blood test. This means that the doctor takes a sample of blood from the person and sends it to a laboratory for testing. The staff then checks how many specific IgE antibodies are present. 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 person has a skin condition that could interfere with the skin test, or if the skin test is too stressful, for example due to other serious allergies. Food allergies can be identified through blood tests, but they can also provide clues if an allergy to pollen, dust mites, animal hair or medication is suspected.
Although this test requires a doctor to draw blood, some people find it more pleasant than a skin test, for example, because it does not expose the body to allergens.
However, blood tests can only determine the cause of an allergy because the body produces specific antibodies depending on the allergen.
However, an allergy test using blood tests cannot provide any information about the severity and type of allergy symptoms. The costs for such a test vary, but are usually covered by health insurance.
This term refers to an allergy test in which the doctor applies an allergen to the mucous membranes of the affected person, where the symptoms mainly manifest themselves. Stimulus tests can indicate an 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 doctor applies a suspected allergen to the mucous membranes. This is done 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 swallowing (orally). Then it is a matter of waiting (under medical supervision!) to see whether and how the body reacts.
Even if no acute allergy symptoms are noticeable immediately before the provocation, a doctor must be prepared to perform skin tests and especially irritation tests so that he can react quickly to possible severe allergic reactions.
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Conclusion
What should you generally bear in mind? Finding an allergen is a step-by-step process: After consulting a doctor, a skin test is usually carried out first. Blood tests are used when a skin test is difficult or too risky. In addition, some allergens are not available as ready-to-use solutions for skin tests. A provocation test only makes sense if a skin test or blood test does not produce a clear result.
A skin test is also important to tell your doctor if you have a lung disease, skin disease 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.
Your doctor will decide which type of allergy test makes the most sense for you.
FAQ: Frequently asked questions about allergy testing
What is an allergy test and how does it work?
What is an allergy test and how does it work?
An allergy test examines whether your immune system overreacts to certain substances, so-called allergens. This can be done using various methods, for example a blood test that measures specific antibodies against allergens.
Which allergies can be detected with an allergy test?
Which allergies can be detected with an allergy test?
An allergy test can detect numerous allergies, including pollen allergies, food allergies, pet dander allergies, dust mite allergies and insect venom allergies. The tests cover a wide range of common allergens.
Are blood tests for allergies more reliable than skin tests?
Are blood tests for allergies more reliable than skin tests?
Blood tests have the advantage of measuring specific antibodies in the blood and thus providing accurate results without the risk of an allergic reaction during the test. They are particularly useful for people with sensitive skin or when testing for multiple allergies at the same time is necessary.
How do blood allergy tests differ from other methods?
How do blood allergy tests differ from other methods?
Blood tests are an accurate and safe way to detect allergies. While skin tests are often local and limited, blood tests provide a more comprehensive analysis as they can test for multiple allergens at once. They are also less stressful as there is no direct exposure to the allergen.
Can a capillary blood test be used for allergies?
Can a capillary blood test be used for allergies?
Yes, capillary blood tests can also be used to detect allergies. These tests are easy to perform and provide a convenient way to diagnose allergies without the need for a complex skin test. They allow a wide range of allergens to be tested with just a small drop of blood.
How quickly do I receive the results of an allergy test?
How quickly do I receive the results of an allergy test?
The results of an allergy test are usually available within a few days. You will receive a detailed evaluation of the allergens tested and find out which substances your body may be allergic to.
How do I prepare for an allergy test?
How do I prepare for an allergy test?
There are no special preparations for most allergy tests, but it is important to tell your doctor if you are taking medications such as antihistamines, as these may affect the test result.
How can I interpret the results of my allergy test?
How can I interpret the results of my allergy test?
The results show which allergens your immune system reacts to. It is recommended to discuss the results with a doctor to plan possible steps to treat or avoid the allergens.
What is the advantage of an allergy test at home?
What is the advantage of an allergy test at home?
An allergy test at home offers the advantage of being convenient and stress-free. With a capillary blood test, you can be tested for a wide range of allergens without having to see a doctor. The sample is simply sent in and the results can be viewed online.
How is an allergy test performed at Probatix?
How is an allergy test performed at Probatix?
With Probatix you receive a test kit for taking blood. You take a small amount of capillary blood and send the sample to our partner laboratory. After a few days you can access the detailed results online and get information about which allergens your body reacts to.
