Allergic diseases are among the most common and prevalent chronic diseases in the world today. An allergen is a harmless substance known to cause an immune response, resulting in an allergic reaction.
Atopic allergy refers to the genetic tendency of an individual to develop allergic diseases such as asthma, atopic dermatitis (eczema), and allergic rhinitis. In such situations, the affected person shows a heightened immune response towards the allergens, particularly those that may be inhaled or ingested. The total serum IgE levels of a person get elevated whenever the immune system is activated after inhalation, ingestion, or diffusion of allergens through the skin. Immunoglobulin E (IgE) is an antibody produced during a hypersensitivity reaction to an allergen. An allergy blood test measures IgE in the body.
On the contrary, non-atopic allergies are those that are not dependent on IgE but still induce an abnormal immune response to certain external environmental factors. To diagnose these allergies, certain skin prick tests and allergy panel tests need to be carried out. A special test called the Phadiatop test is beneficial in ruling out the presence or absence of an atopic allergy.
Some of the common atopic and non-atopic allergies are briefly described below:
- Atopic dermatitis: This is most commonly seen in young children but can affect people at any age and carries a genetic predisposition. It is characterized by dry, itchy, and flaky skin that may become inflamed. Atopic dermatitis causes are multifactorial in nature. It may develop when the skin’s barrier system gets compromised, making it vulnerable to irritants and allergens. Many food items can also trigger atopic dermatitis, such as peanuts, cow’s milk, eggs, seafood, wheat, etc.
Some common atopic dermatitis symptoms are as follows:
- Dryness of the skin
- Swelling and inflammation
- Itching that can turn severe
- Red, brown, or purple-colored rashes
- Tiny, fluid-filled bumps with crust formation
2. Atopic eczema: While both dermatitis and eczema result in inflammation of the skin, the term “eczema” holds a broader meaning for a group of conditions. Atopic dermatitis is the most commonly seen form of eczema. The Academy of Allergy and Clinical Immunology (EAACI) has come up with the term atopic eczema-dermatitis syndrome to signify atopic dermatitis.
3. Allergic rhinitis: In many cases, it is observed that children with atopic dermatitis also tend to develop allergic rhinitis or asthma later in life. It is commonly known as hay fever and causes sneezing, itchy nose, congestion, and sore throat. Allergic rhinitis is an allergic reaction in response to certain tiny particles that float in the air, such as pollen, dust mites, pet dander (fur, hair, feathers), etc.
Allergic rhinitis symptoms may include one or more of the following:- Itchy eyes, nose, and throat
- Fatigue and general malaise (discomfort)
- Increased mucous in the nose and throat
- Coughing, wheezing, and difficulty breathing
- Nasal congestion (stuffiness), runny nose, or sneezing
4. Atopic asthma: Allergic asthma is often called atopic asthma, and it is triggered by certain allergens in the air such as pollen, dust mites, and pet dander. Atopic asthma is mostly seen in younger people, whereas non-atopic asthma is commonly observed in people of older age groups. Symptoms of atopic asthma include coughing, wheezing, shortness of breath, itchy eyes, stuffy nose, and experiencing chest tightness.5. Hyper IgE syndrome: It is a rare primary immunodeficiency disease marked by repeatedly occurring eczema, skin abscesses, recurrent respiratory infections, eosinophilia, and elevated IgE levels in the blood. It may be inherited in either autosomal dominant (AD) or autosomal recessive (AR) forms.
6. Contact dermatitis: This is a classic example of a non-atopic allergy. It is most commonly caused by sensitization to external substances such as nickel, chrome, mercury, and lanolin, or even due to cosmetic use. It is characterized by symptoms such as redness, itching, scaling, and thickening of the skin (lichenification) at the site of exposure to the irritant. This disease is non-IgE-mediated.
Diagnosis
- Phadiatop test
This is an in vitro test that detects allergen-specific IgE antibodies that play a role in IgE sensitization during early childhood. This allergy screening test shows excellent sensitivity and specificity for inhalant allergens, including grasses, weeds, molds, cat and dog dander, as well as house dust mites.
The purpose of the Phadiatop test is to confirm the presence or absence of atopic allergy. It also helps in identifying patients who may need further evaluation with specific IgE testing. This test enables doctors to easily identify allergens that are causing the symptoms, thereby helping them choose the most befitting treatment options.
What is Phadiatop positive?
- A positive Phadiatop test result means that the person is allergic to either one or more of the inhalant allergens. With the help of this test, a qualitative serological assessment can be made because of the fluorescence response obtained in the result. If the patient’s sample produces a fluorescence response equal to or higher than the reference serum, it indicates a positive Phadiatop test. Thus, Phadiatop is a very useful test when it comes to differentiating between atopic and non-atopic allergies and can be employed in the differential diagnosis of IgE-mediated diseases in children.
- Allergy Panel test
An allergy panel test against a particular allergen includes various tests such as skin prick (scratch) test, intradermal skin test, blood test (IgE), challenge test, etc. However, an atopy patch test is conducted for further differentiation between atopic and non-atopic allergies.
An atopy patch test is similar to the patch test used in the diagnosis of contact dermatitis. In this test, a suspected allergen is directly applied to a clinically unaffected and untreated patch of skin on the back. It is allowed to remain as such for at least 48 hours before evaluation. After the said period, if a rash or reaction is noticeable, it indicates a positive reaction to that specific allergen.Atopic and non-atopic allergies are the two types of allergic reactions exhibited by the body in response to different allergens. It is important to find out the particular allergen that is causing the symptoms for an effective treatment. Various diagnostic tests are available that can help rule out whether the allergy is atopic or non-atopic, such as the Phadiatop test. Be it a food or an inhalant allergen, with appropriate treatment measures, the symptoms can be controlled and managed to a great extent.
