When I have a runny nose and sneezes every season, I think, “I should get an allergy test.” However, when you go to the hospital, you are informed of two types of tests, one that involves dropping a reagent on your arm and the other that involves drawing blood, and it is often difficult to decide which one to choose.
The two tests do not look at the same thing in different ways, but the point at which they are checked is slightly different. Below we have outlined the differences between principles and practice, how the results should be read, and where costs diverge.
Summary
- Skin prick testing is a method of applying a small amount of antigen to the arm or back and checking for a wheal reaction 15 to 20 minutes later.
- Serum-specific IgE tests (MAST, ImmunoCAP, etc.) measure IgE antibodies for each antigen through blood collection and do not require medication discontinuation.
- Total IgE and eosinophil levels are reference indicators of allergic tendencies but do not indicate the causative agent.
- A positive test indicates ‘sensitization’ and does not confirm that the substance is causing your symptoms.
- Costs vary with the number of allergens tested and whether National Health Insurance coverage criteria are met, so prior confirmation is required.
1. How the two tests differ in principle and practice
1-1. Skin prick test
Drop the suspected antigen solution drop by drop on the inside of the forearm or back and gently prick it into the epidermis. When IgE for the corresponding antigen attaches to skin mast cells, histamine is released, causing wheals and redness. After 15 to 20 minutes, the size is compared with the positive control (histamine) and negative control (saline solution).
The advantage is that you can see the results on the same day and confirm them with your own eyes. However, if you are taking antihistamines, the reaction may be suppressed and false negatives may be obtained, so the medication usually needs to be stopped several days before testing. Some antidepressants or systemic steroids may also have an effect. It is difficult to read if you have severe dermatosis or extensive eczema.
1-2. Serum-specific IgE test
A single blood draw measures the concentration of IgE antibodies against multiple antigens. The MAST series is a screening method that bundles multiple antigens on one plate, and the ImmunoCAP series provides relatively precise quantitative values for each antigen. There is no need to stop taking the medication, it is independent of skin condition, and it is safe as there is no risk of anaphylaxis. Instead, it takes several days for results to come out.
| Category | Skin prick test | Serum-specific IgE test |
|---|---|---|
| Method | Observation of wheals after application of antigen to the skin | Measurement of antibody concentration after blood collection |
| Takes | Read within 15 to 20 minutes on the same day | Laboratory processing time required |
| Antihistamines | Medication must be stopped beforehand | No medication interruption required |
| Skin condition effects | Restrictions in cases of eczema or dermatitis | No effect |
| Pediatric application | Consider the child’s ability to cooperate and discomfort | Possible with one blood draw |
| Antigen number | Selection based on clinical judgment | Dozens of types depending on panel configuration |
In the case of children, it is difficult to uniformly say which is better. If a child has difficulty enduring the multiple pricking process, blood collection may be better; on the other hand, blood collection may be more burdensome in some cases. At the clinic, the decision will be made based on the child’s condition and the range of antigens to be checked.
2. What do total IgE and eosinophils tell you?
The total IgE that appears on your blood test result is the total amount of IgE in your entire body. Although it tends to be elevated in people with allergic constitution, it also rises in parasitic infections and some diseases, and conversely, there are people whose levels are within the normal range even if they have clear allergic rhinitis. In other words, it is difficult to diagnose or rule out total IgE alone.
Peripheral blood eosinophil levels and eosinophil findings in nasal smears are also references for estimating the degree of allergic inflammation. Neither will tell you “what you are allergic to.” To narrow down the causative agent, an antigen-specific IgE test or skin prick test is required.
3. Not every positive result identifies the cause — sensitization vs. clinical allergy
Even if the test comes back positive for dust mites, it does not necessarily mean that your current stuffy nose is due to mites. A positive test means that IgE has been produced (sensitization) to that antigen, and clinical allergy is a condition in which symptoms actually appear when exposed to that antigen. There are quite a few people who are sensitized but have no symptoms.
Therefore, interpretation of results becomes meaningful only when combined with a symptom diary. By comparing when it gets worse, whether it varies depending on the season and location, and whether it only appears in certain environments, we select which of the positive test items is most likely to be the actual cause. Conversely, in some cases the symptoms are clear but the test is negative, the possibility of local allergic rhinitis or non-allergic rhinitis is also considered.
4. Cost structure and confirmation method
Allergy testing may be covered by Korea’s National Health Insurance when symptoms and clinical need are documented. However, even for the same test, the degree of out-of-pocket expenses varies depending on the number of items, test method, and whether the recognition standards are met, and any portion that falls outside the standards may be treated as a full out-of-pocket expense or non-covered care. This is where the amount varies.
| Factor | Cost Impact |
|---|---|
| Number of test antigens | The total amount increases as the number of items increases. |
| Test method | Differences in calculation methods between screening panels and quantitative tests |
| Insurance coverage | Reduction of out-of-pocket cost when clinical findings/standards are met |
| Additional tests | Separate calculation of total IgE, blood test, nasal endoscopy, etc. |
The exact amount can be estimated only after a consultation determines which tests are needed. It is realistic to ask which tests are performed and how many items are performed during treatment, whether they are covered or not, and check the estimated cost from the hospital administration department. The non-covered amount by hospital can also be referenced in the Health Insurance Review and Assessment Service’s public data on non-covered medical expenses.
5. Situations where testing is actually helpful
Not all nasal symptoms require testing. Results become more meaningful if they change subsequent judgments.
- When designing avoidance therapy: Knowing the causative antigen allows you to decide on specific measures such as bedding management, contact with pets, and preparation for each season.
- When considering immunotherapy (sublingual/subcutaneous): Identifying the antigen is required to determine which antigen to treat with.
- When drug response is different than expected: This serves as data to examine the possibility of causes other than allergies.
- When looking at progress in children: It serves as a baseline to check whether sensitization patterns change over time.
Conversely, if the cause is already clear and controlled through avoidance and medication, broadening the scope and repeating the test may not significantly change the judgment.
Frequently Asked Questions
Q. How many days should I stop taking the medication before a skin test? A. It depends on the type of drug. Antihistamines are usually recommended to be discontinued a few days in advance, and the period varies depending on the ingredients and half-life. There are some medications that should not be stopped voluntarily, so please inform your doctor of the list of medications you are taking and receive guidance on whether to stop and for how long.
Q. Do I need to take both tests? A. Testing usually starts with one method. However, supplementary tests may be added when test results and symptoms do not match or when specific antigens need to be identified more precisely. It is not always advantageous to do both from the beginning.
Q. The test result is negative, but the symptoms persist. A. There may be other causes such as non-allergic rhinitis, local allergic rhinitis, structural factors such as nasal septum deviation, and drug-induced rhinitis. A negative test does not mean “no abnormalities,” so if symptoms persist, it is best to get an evaluation from a different angle.
This article is general health information and is not a substitute for individual medical care. If symptoms persist or worsen, please seek treatment at a medical institution.