An allergy is a protective reaction of the human immune system to actually harmless substances such as pollen, dust, or food. The more sensitive the immune system reacts to the allergen, the stronger the symptoms. Allergies can cause watery or red eyes, sneezing, runny nose, itching, or stomach upset.
Rarely, an allergic reaction can also cause anaphylaxis. This causes the airways to narrow, leading to severe shortness of breath and a significant drop in blood pressure. Without immediate treatment, such a shock can be fatal.
To find out which substance triggers an allergic reaction, various tests can be conducted: skin tests, blood tests, and so-called irritation tests. A suitable allergy test is usually found as a result of a symptom and medical history description in the doctor's office.
What are skin tests?
Skin tests can be performed quickly and easily, which is why they often represent the first line of diagnosis. In a skin test, potential 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 may have heard the term, as 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 procedure.
During a skin examination, the doctor examines various allergens or the patient's reactions to them. In such a test, the doctor applies a watery solution containing an allergen like pollen or traces of animal hair to marked skin areas. The skin is then lightly scratched with a lancet to allow the allergens to penetrate.
This allergy test can detect immediate reactions, which is why it is useful when there is suspicion of so-called immediate allergies, i.e., physical reactions that occur within a few minutes.There is a standard range for skin tests that includes about 15–20 solutions with the most common allergens. Doctors always conduct 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. If this is the case, the skin may generally overreact.
In the skin test, the negative control is histamine. An obvious reaction, such as nodule formation, is not a sign of an allergy but is desired. These two solutions ensure that the results of the sting test are evaluable, more precisely usable.
It is important that 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 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.
However, the difference is that the doctor injects the allergen into the skin (intradermal injection) instead of just applying it superficially to the skin. This allows the test to detect weaker allergic reactions.
Such an allergy test is usually only used if the previous skin test did not provide suitable results. This is because the injection is usually more irritating for the affected individuals, 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 trigger a stronger allergic reaction, it is only recommended if the prick test does not show a 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 intradermal test.
“Scratch” is the English word for “Kratzer” – and in this allergy test, the name says it all. The doctor scratches the skin surface (but does not cause bleeding) and rubs the suspected allergen onto the skin at this spot. This friction allows the corresponding allergens to penetrate deeper into the tissue, which is why this allergy test is often chosen as an option when a skin test does not yield 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 example, for liquids and water-soluble substances, including food or medication allergy tests. If the affected person is allergic, redness and swelling occur within about 20 minutes.
The patch test (patch or plaster test)
In this allergy test, your doctor will apply a patch with the test substance to your skin, so the skin remains intact and does not need to be scratched for this allergy test.
With these patches, doctors can apply up to 4,000 potential allergens to the back or the inside of the forearm – of course, not all at once. Typically, the doctor first examines the so-called standard series, which are the 27 substances listed in the test series of the German Dermatological Society that most frequently cause allergies.
After 20 minutes, the doctor first checks if there is a reaction under the test patches. Two follow-up checks after 24 hours each confirm or refute the result. Subsequently, the patch is evaluated, meaning your doctor will check if and to what extent papules, blisters, and other allergic reactions have formed under the patches.
Which allergens can be detected with this allergy test? Allergens that trigger so-called delayed-type reactions. In other words, if an allergy is suspected and the symptoms appear hours or days after contact with the allergen, a doctor usually performs a skin test.
Which substances are commonly tested?
- Preservatives and fragrances
- Nickel or cobalt
- Latex
- Medications
The friction 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 compared to the rub test. The substance is applied to the skin and the skin surface is scratched. Here too, the allergic reaction occurs after about 20 minutes.
The blood test
Your doctor can diagnose allergies with a blood test. This means the doctor takes blood from the affected person 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 "Immunoglobulin E" and refers to proteins that the body produces in response to or to avoid allergies.
A blood test is an option if the affected person has a skin condition that could affect the skin test, or if the skin test is too stressful, for example, due to other severe allergies. Food allergies can be detected through blood tests, but they also provide clues when there is a suspicion of an allergy to pollen, house dust mites, animal hair, or medications.
Although a doctor must draw blood for this test, some people find it more pleasant than 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.
Conclusions about the severity and type of allergy symptoms cannot be drawn from a blood test allergy test. The costs for such a test vary but are usually covered by health insurance.
Behind this designation lies an allergy test in which the doctor applies an allergen to the mucous membranes of the affected person, where the symptoms mainly manifest. Stimulus tests can indicate an allergy when other tests are inconclusive or not definitive. 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 through inhalation by the patient or – in the case of food or drug allergies – by ingestion (oral). Then it is a matter of waiting (under medical supervision!) to see if and how the body reacts.
Even if no acute allergy symptoms are noticeable immediately before the provocation, a doctor must be prepared for skin tests and especially provocation tests, so that he can quickly respond to possible severe allergic reactions.
Conclusion
What should be considered in principle? Identifying an allergen is a step-by-step process: After consulting a doctor, a skin test is usually performed first. Blood tests are used when a skin test is difficult or too risky. Additionally, 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 provide a clear result.
A skin test is also important to inform 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 like ASA or Ibuprofen.
The attending physician decides which type of allergy test is most appropriate for you.
FAQ: Frequently Asked Questions about Allergy Tests
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, known as allergens. This can be done through 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?
With an allergy test, numerous allergies can be detected, including pollen allergies, food allergies, pet hair allergies, house 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 offer the advantage of measuring specific antibodies in the blood, providing accurate results without the risk of an allergic reaction during the test. They are particularly useful for people with sensitive skin or when simultaneous testing for multiple allergies is necessary.
How do blood allergy tests differ from other methods?
How do blood allergy tests differ from other methods?
Blood tests are a precise and safe method for detecting allergies. While skin tests are often conducted locally and are limited, blood tests offer a more comprehensive analysis as they can test for multiple allergens simultaneously. Additionally, they are less burdensome 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 offer a convenient way to diagnose allergies without the need for an elaborate skin test. They allow testing for a variety of allergens with just a small drop of blood.
How quickly will I receive the results of an allergy test?
How quickly will 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 analysis of the tested allergens 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?
For most allergy tests, no special preparations are required. However, it is important to inform your doctor if you are taking medications such as antihistamines, as these can 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 for treatment or avoidance of the allergens.
What is the advantage of a home allergy test?
What is the advantage of a home allergy test?
A home allergy test offers the advantage of being convenient and stress-free. With a capillary blood test, you can test a wide range of allergens without having to visit a doctor. The sample is simply sent in, and the results are available online.
How is an allergy test conducted at Probatix?
How is an allergy test conducted at Probatix?
With Probatix, you will receive a test kit for blood collection. 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 gain insight into which allergens your body reacts to.
