Since allergy is a very complicated and multifaceted disease, its diagnosis also involves a multipronged approach. It is based on a combination of history, signs and symptoms, laboratory tests and special tests for allergy.
The history is a fundamental part of diagnosis of allergic disease. There are certain questions that need to be asked, e.g., What are the symptoms? Do they occur in a particular place (ie. home, workplace)? Time of the day, season, after consuming certain food or medicines, after exercise, related to stress or not – are vitally important questions to be explored. Past history of same allergy or other related condition may be related to the current illness. Family history of similar allergic reactions is also significant.
Besides the history, physical examination is another equally important part of the diagnosis of allergy. It is important because there are characteristic findings of allergy which are different from non-allergic conditions but may have similar history and symptoms. Complete examination of the eyes, ears, nose, throat, lungs, skin and abdomen is essential.
The final step in making the diagnosis is done by ordering laboratory tests and investigations, which form the basis of the full and final diagnosis of allergy.
The tests which are commonly used to diagnose different types of allergies are as follows:-
□ Blood tests
□ Allergy testing
□ X-rays, CT Scan, Magnetic Reasonance Imaging (MRI)
□ Culture and Sensitivity. Blood Tests
Among the blood tests, the important tests are the white blood cell (WBC) counts. These cells are important because they help the body in fighting against any infection as well as entry of foreign body into the system. In most of the allergies, Eosinophil, a type of WBC is increased in number in the blood.
In some cases, measurement of total immunoglobulins (Ig) in the blood is useful in differentiating the symptoms between allergic and non-allergic conditions. This is very useful in the diagnosis and treatment of the disease.
Allergy Testing
Allergy testing is usually done by two methods – skin testing and determination of allergen-specific IgE in the blood by Radio Allergosorbent Test (RAST). For skin testing, a small drop of the allergen is touched with a needle and the skin is pricked with it. In sensitive individuals, there will be redness and swelling at the site of the prick within 15 to 20 minutes. For further confirmation, a more dilute allergen is injected into the skin and looked for similar changes. In people who are very sensitive to the skin testing or are suffering from some skin disease, blood levels of allergen-specific IgE is a useful alternative. This test is also useful for detecting food allergies. It can help in detecting different types of allergens to which the person is sensitive.
X-Ray/CT Scan/MRI
Besides the above tests, X-rays, CT Scan and MRI of the nasal sinuses and lungs can help in detecting the nature of the illness. These tests help in differentiating between the allergic diseases and non-allergic ones.
Culture and Sensitivity Tests
In allergic illnesses, you can hardly find any disease-causing bacteria. This fact can be proved by taking different secretions from the nose, throat, eyes, lungs, stool, etc. and keeping them in the laboratory for 24-48 hours to observe any growth of bacteria.
These are referred to as culture and sensitivity tests. These tests help in determining the line of treatment the individual will need to overcome his illness.