The Concept of Allergy Testing and Its Medical Importance

An allergy refers to the adverse clinical symptoms of the interaction between an allergen-specific IGE and exposure to an allergen. Common allergic reactions due to exposure to an allergen include allergic rhinitis, sinusitis, conjunctivitis, urticaria, asthma, irritable bowel syndrome, among many others. Other non-IGE mediated factors such as viruses and irritants may also cause allergies. All medical sample like FFPE are to be handled very carefully so only reputed agencies should be assigned such tasks.

Allergy Testing and Its Medical Importance

Diagnosis of Allergies

History taking is one of the essential tools allergists use to diagnose allergies. However, when history taking, medics should be alive to the common types of aeroallergens and where they are found in the environment, plus the factors that can increase the likelihood of exposure. Perennial allergens such as dust fleas, dander, and indoor molds are present year-round and, therefore, likely to cause persistent symptoms.

Patients’ clinical histories are ideally sufficient to inform whether the diagnosis is an allergy and if so, the remaining question is to find out what the patient is allergic to. However, if the history alone is used, diagnostic testing will come in handy in pinpointing the direct causative agent of the allergy.

Provocation or Challenge Test

The most effective allergy test should identify patients with 100% specificity to the allergy and those with 100% sensitivity. The most important and widely used allergy tests include the provocation or challenge method. In this case, the patient is exposed to a stimulus similar to the allergen suspected of having caused the allergic symptoms. For allergic rhinitis, it can be done with nasal instillation of allergen. While for asthma, bronchial stimulation can be used.

Sting tests can be used for food and drug allergies. However, these gold-standard tests are usually expensive and complicated and can be performed with a choice of allergen, one at a time.

Surrogate Tests

Surrogate tests are more accessible to perform and less expensive than direct gold tests. Further, these tests have been proven to be safer and more convenient. What more? Surrogate tests can predict the results of the gold standard allergy tests.

To gauge the success of allergy tests, doctors should examine their likelihood ratios. A likelihood ratio is the odds ratio that a positive test result for a patient will turn positive instead of negative. A sizeable positive ratio increases the odds that a patient whose test yields positive results has higher chances that they have the disease. Conversely, a patient whose test results yield a small negative test is highly likely to have the disease.

There are two significant diagnostic tests to test for allergies with the presence of specific IgE antibodies:

• Allergy skin tests
• In-vitro tests

Allergy Skin Tests

Allergy skin tests are performed to identify IgE antibodies bound to mast cells on the skin. If specific IgE antibodies are present, the allergen induces histamine to be released, resulting in wheal and flare. Wheal and flare is the characteristic reddening and swelling of the skin resulting in bumps (due to the influence of chemicals such as histamines) released by the body when introduced to an allergen. The wheal and flare reaction is then measured, and if larger than the negative control, it’s considered positive.

Intracutaneous Test

Intracutaneous means within the body, under the skin. It involves injecting a solution of 0.05 ml of dilute water extract under the skin of the patient arm. However, intracutaneous tests may be too sensitive and therefore nonspecific, which usually leads to a significant incidence of false-positive tests.

Percutaneous Tests

This test involves pricking the patient’s skin with a sharp object, then introducing a solution of 1:40 in the presence of the allergen, introducing the wheal and flare as described above.

Importance of Skin Allergy Tests

The advantage posed by skin allergy tests is that they are rapid, specific and safe, and relatively inexpensive. This efficiency and rapid nature of skin test aid allergists in determining the specific allergen that affects their patients, making allergy mitigation efforts faster and easier for a better patient lifestyle.

The disadvantage of skin tests is that they pose a risk of a systemic reaction, which may be fatal in the absence of immediate resuscitation efforts. Further, some patients find it uncomfortable and experience body discomfort upon introducing these allergens. In addition, patients who have taken antihistamines before these tests may yield a false negative. Allergists should therefore advise their patients days before performing these tests for accurate results. Consequently, patients who are on antihistamines and cant be discontinued for a duration to perform these tests are not candidates for these tests. Ironically, they are the ones who need these tests most.

Trained allergists also have a variation on how they perform these skin tests and how they interpret and even document these tests. This can pose a challenge to data interpretation and an agreed mitigation procedure done in other medical tests.

Invitro Tests

Invitro tests involve using a patient’s serum to test the presence of specific IgE antibodies, which are detected using an enzyme-conjugated anti-IgE, which causes a substrate to be fluorescent or to turn color.

The advantages of in-vitro tests are that they are readily available in hospital and lab settings. The most significant importance of this method is that it is performed in-vitro instead of invivo. Invitro tests are done outside the human body, in laboratory equipment, under a controlled environment. Therefore, the patient is not exposed to the allergen and thus is not at risk of systemic reaction or allergen-caused discomfort. The test can also be performed on patients o antihistamine since antihistamine intake does not affect this test. The only disadvantage is that it is more expensive when compared to the other tests.

Many people today suffer from allergies. The development of lifestyle diseases has not helped this situation either. A significant number of fatalities in the hospital are also due to anaphylactic shock- caused by systemic allergic reactions. Lifelong allergies like asthma and rhinitis, and at other times, urticaria should also be well managed with precision on the causative agent. Therefore, seeking the services of an allergist is of utmost importance for a healthy, longer life.