Allergic reactions tend to have a drastic effect on the quality of life. If you want to make it certain that you are able to lead a healthy life, it is important to find out the culprit allergen which is the root of all the problems you have been facing. However, this is easier said than done.
What to Expect?
A number of allergic tests are conducted to reveal the allergen a person is allergic to so that a proper treatment plan can be formulated. The best way to deal with an allergy is to find out the stimulant and avoid exposure to it. Allergic tests aim to do this.
Before we proceed to shed some light on the interpretation of test results, we feel it prudent to mention that interpreting these tests can get quite a bit tricky. This is owing to the fact that the incidence of false positive is rather high.
False positive results imply that as per the testing, you are allergic to something, while the reality is somewhat different. This can be highly confusing.
Furthermore, there are different types of tests done for allergies and the interpretation differs accordingly.
Let us first talk about the test which is most commonly done to find out the stimulant of an allergic reaction, which is the skin test. Three types of skin tests are usually conducted, which include a skin prick test, intradermal test and patch test.
In case of skin tests, a red, itchy area which is slightly raised, referred to as a wheal, develops on the spot where the allergen was pricked into the skin. This is called a positive reaction implying that you are allergic to that specific allergen.
Blood tests can also be conducted to check for the responsible antigen with the options commonly used include ELISA and RAST tests. In these tests, the blood is checked for levels of immunoglobulin E which is the antibody associated with allergies.
If the results of any of these tests are not negative, you will need to acquire a consultation with an allergist who would be able to guide you in the right direction.
How to Read Allergy Test Results
The thing that needs to be kept in mind is that these tests tend to be interpreted differently due to which comparing the numbers between them might not provide you with the clarity you are looking for. The common belief is that a higher number indicates that you are more sensitive to that particular antigen.
When we talk about RAST testing, the range differs from lab to lab depending on the techniques they use. The range can lie anywhere between 0.1 and 10 kU/L. The test revolves around measuring specific IgE levels that are directed toward the food in the blood.
These tests have low positive and high negative predictive value. It is quite common to encounter mild elevated results, particularly in children who have allergic conditions like asthma, eczema and allergic rhinitis.
The predictive values differ with every food item. However, it is said that the higher the level, the more chances there are of an IgE mediated allergy being present. Owing to false results, this is said to be a poor screening test.
Another test used for allergy is a physical supervised challenge test. In this test, the patient is made to consume an increased amount of suspected food allergen under the supervision of a physician.
If no symptoms occur which can be an indication of IgE mediated allergy, it implies that you are not allergic to that food item. The test tends to take around 4-8 hours but is found to be highly reliable.
Thus, it is apparent that the interpretation of allergy test results is not as simple as it seems. There are high chances of errors, which is why it is important that you get these tests done from the right place so that it can be ensured that you get authentic and reliable results.
Allergy Test Results Scale
Some grading scales have been formed to increase the accuracy of the test result. The size of a wheal is used to gauge the sensitivity. Keep in mind that the size is meant to provide you with information regarding the severity of the antigen and is not an indication of the severity of the symptoms.
- If the wheal size is less than 4 mm with the score being 0+, the result is negative.
- If the size is between the range of 5 and 10 mm with a score of 2+, the interpretation is mildly sensitive.
- For wheals between the size of 10 and 15 mm and a score of 3+, the result is moderately sensitive.
- If the size of a wheal is more than 15 mm with a score of 4+, it indicates very high sensitivity.
It is imperative that the skin tests are interpreted keeping the history and physical examination of the patient in mind. This ensures that the doctor is able to decipher the results accordingly. It is also important that the doctor has information regarding the reasons that can lead to false positives and negatives.
One of the reasons for an error in a skin prick test is when the tests are placed too close together, that is, less than 2 cm apart. This is why the solution needs to be spread. Irritant reaction can also lead to false positive results.
False negative results can occur owing to the use of medications such as antihistamines which is why the medicines need to be stopped 72 hours prior to the tests.
In infants and the elderly, reactivity of the skin is decreased, which is why false negative results can be acquired. Diluted allergen extract can also be a reason for false negatives.
Sometimes, people are certain about the allergen responsible for an allergic reaction which is why they tend to be rather surprised with the negative results and end up doubting their reliability. However, there is always a possibility that you are allergic to another material.
Therefore, make sure that you communicate all your doubts to your allergist so that they can guide you accordingly.