The skin test is the most common type of allergy test. It is a type of diagnostic procedure used to determine whether you are allergic to a specific substance or not. In this article, we will discuss how to read allergy skin test results and what they mean.
Your skin will be exposed to allergens (allergy-causing substances) during allergy skin testing. The skin will then be monitored for allergic reactions.
Allergy tests can be used to verify a substance you are allergic to, whether it is something you eat, touch, or breathe.
Your doctor may use information from allergy tests to help you develop an allergy treatment plan, which could include medication, allergen avoidance, and allergy shots (immunotherapy).
Table of Contents
Allergy skin tests
A skin prick test also called a puncture or scratch test is a method for identifying instant allergic reactions to as many as 50 substances at once. Not only does this test identify allergies to common substances like pollen, dust mites, and mold, but it can also identify food allergies. This test is usually done on the arm in adults, but the site of the test varies depending on the substance being tested for.
It may take several days for a patch test to show results. Positive skin tests can indicate that you are allergic to a substance. A greater level of sensitization is usually indicated by larger wheals. Negative skin tests are a sign that you’re not allergic to any particular allergen.
An allergy test for skin can cost anywhere from $60 to $300. A blood test costs $200-$1,000. A test for food allergies and chronic hives may cost hundreds of dollars. These tests may not be covered by your health insurance.
To diagnose allergies, allergy skin tests can be used extensively.
- Allergy to asthma
- Bee venom allergy
- Eczema (dermatitis)
- Allergies to food
- Allergic rhinitis (hay fever)
- Penicillin allergy
All ages and genders can use skin tests, even infants. However, skin tests may not be recommended in certain situations.
24 hours prior to the test avoid caffeine-containing foods, beverages, or medications, including coffee, tea, and chocolate. It can be difficult for both you and your healthcare provider to identify caffeine as the cause of allergy symptoms. It can also be difficult to determine if it is a food allergy.
If you are not sure, your doctor might recommend skin testing.
Never experienced a severe allergic reaction. Anaphylaxis is a condition whereby you are so sensitive to certain substances, even tiny amounts in skin tests, that they can trigger a life-threatening reaction.
Do not take any medication that may interfere with the test results. Antihistamines, antidepressants, and heartburn medications are all possible. You may be advised by your doctor to continue using these medications, rather than discontinue them temporarily to allow for a skin test.
You may have certain skin conditions. Severe eczema and psoriasis that affect large areas of your skin, such as the back or arms – which are the usual testing locations – may mean there is not enough clear skin for an effective test. Test results can be skewed by other skin conditions such as dermatographism.
For those who are unable or unwilling to undergo skin testing, blood tests (in vitro immunoglobulin E antibody test) may be helpful. Penicillin allergy is not a reason for blood tests.
Allergy skin tests can be used to diagnose allergies to airborne substances such as pollen, pet hair, and dust mites. Food allergies can be diagnosed by skin testing. Food allergies can be complicated so you might need to have additional tests.
A skin test is performed to determine if an allergen (or substance) could trigger an allergic reaction. Allergens that can trigger allergic reactions (aeroallergens), such as furry animals, pollens from trees, grasses and weeds, and molds, can lead to symptoms in the eyes, nose, and throats.
Foods, medications, latex, and insect venoms are all possible allergens that could trigger allergic reactions.
Peanuts, wheat, and eggs are all common food allergens. These foods can cause itchiness and may lead to flare-ups, or worsening of dermatitis symptoms.
Drink more water, juice, or other non-alcoholic beverages if you feel stuffy, have a postnasal drip, or are feeling irritable due to allergies. Extra liquid can help thin your mucus and provide some relief. Steam is a benefit of warm fluids such as soups, broths, and teas.
Contact dermatitis (CD) is an inflammatory skin disease caused by chemicals or metal ions that exert irritant (toxic) effects, or by small reactive chemicals (contact allergens) that modify proteins and induce immune responses (predominantly by T-cell response).
Acute allergic CD develops after 24-48 hours. Skin lesions are initially asymmetric and limited to the area of contact but often spread/disseminate later. In the case of severe reactions, there is swelling and blistering. There are cases when skin lesions take the shape into some life-threatening.
Itchy redness can occur if you are allergic to latex. Wheals, which look similar to hives, may appear as raised welts. Your immune system may be reacting to skin irritations and wheals.
The percutaneous route involves a solution containing diluted allergen being pricked onto the skin’s surface.
A doctor will usually perform skin testing. The test is usually administered by a nurse, and the results are interpreted by a doctor. This test typically takes between 20 and 40 minutes.
Some tests detect immediate allergic reactions, which can occur within minutes after exposure to allergens. Some tests can detect delayed allergic reactions that develop over several days.
Different types of allergy tests
There are many ways to test for allergies. Based on your symptoms and suspected allergens, your healthcare provider will recommend the best test.
These tests include:
Skin injection test
An intradermal test is a procedure that injects a small amount into your skin. After about 15 minutes, the injection site is checked for allergic reactions. This test may be recommended by your doctor to determine if you have an allergy to penicillin or insect venom.
Skin prick (scratch test)
A provider may use a fine needle to poke your skin on the forearm and back. It could contain 10-50 different allergens. Your provider might place drops of possible allergens on your skin, then use a tool to lightly puncture the skin.
Redness and other reactions such as swelling can occur within 15 minutes. You might experience a rash, raised, or round spots known as wheals. This test can be used to check for penicillin allergy, food allergy, and airborne allergies.
A skin prick test (also known as a puncture test or scratch test) checks for allergic reactions to up to 50 substances simultaneously.
This test is used to determine allergies to foods, pollen, mold, pet hair, dust mites, or pollen. Adults usually test on their forearms. The upper back may be used for children.
Allergy skin testing isn’t painful. This testing involves the use of needles (lancets), which barely penetrate the skin’s surface. It is unlikely that you will feel any bleeding or discomfort other than mild, brief discomfort.
After cleaning the test area with alcohol, the nurse makes small marks on the skin and then applies an allergen extract to each one. The nurse then uses a lancet for pricking the extracts onto the skin’s surface. Each allergen requires a new lancet.
Two additional substances are rubbed into the skin’s surface to check if it is responding normally.
Histamine. This substance triggers a skin reaction in most people. Your allergy skin test might not show a reaction to histamine if you do not have an allergy.
Saline or glycerin. These substances are unlikely to cause an allergic reaction in most people. You may experience sensitive skin if you react to saline or glycerin. To avoid a false diagnosis, test results should be carefully interpreted.
The nurse will observe your skin for allergic reactions approximately 15 minutes after you have pricked it. You may develop a raised, itchy, red bump (wheal) if you have an allergy to any of the substances being tested. This could look similar to a mosquito bite.
The nurse will measure the size of the bump and take the data. The nurse will then clean the skin with alcohol to get rid of the bumps.
Intradermal skin testing
If your skin prick test results were negative or inconclusive, you may be eligible for an intradermal test. The allergen is injected into your epidermis, the outermost layer of your skin. This test is used to check for allergic reactions to medications and airborne irritants.
Patch Tests
This test determines the source of contact dermatitis. The allergen is applied to the skin of your arm by your provider. A bandage is then placed over the affected area. Your provider might apply a bandage (or patch) with the allergen.
The provider will apply the bandage and you can return within 48 to 96 hours. Your provider will then remove the bandage and inspect your skin for any rash or reaction.
It is common to test for allergic skin inflammation using patch testing (contact dermatitis). It is possible to detect delayed allergic reactions through patch testing, which can take up to several days.
The needles used for patch tests are not necessary. Instead, allergens are applied on patches and then placed on the skin.
Your skin could be exposed to up to 30 different substances during a patch test that can lead to contact dermatitis. These substances include latex, medication, perfumes, preservatives, and hair dyes.
The patches should be worn on your arm or back for at least 48 hours. You should not bathe or engage in activities that produce excessive sweating during this period. When you return to the doctor, the patches will be removed. It is possible to have an allergy if your skin becomes red and itchy.
Blood Test (IgE).
A sample of your blood is sent by your provider to a laboratory. The lab will add allergens to your blood and measure the IgE antibodies. False-positive results can be higher in blood tests.
Challenge tests
Only a provider can direct this test. A small amount of the allergen is ingested (swallowed) by people with suspected food and drug allergies. This test is usually performed by an allergist, which is a specialist in allergies. It is important to have medical supervision. Anaphylaxis is a condition in which you experience an allergic reaction. The provider will quickly administer an epinephrine shot to stop the reaction.
How do you read the results of an allergy skin test?
You will know your results from an intradermal or skin prick test before you leave the doctor’s office. It may take several days to get results from a patch test.
Positive skin tests can indicate that you are allergic to a substance. A larger wheel usually indicates a higher level of sensitivity. Negative skin tests are a sign that you’re not allergic to any particular allergen.
Remember that skin tests may not always be accurate. Sometimes they can indicate an allergy even though there isn’t one (false positive), and skin testing might not cause a reaction if you are exposed to something you are allergic to (false negative).
Different people may react to different tests. You may react positively to a substance in a test, but not to it every day.
You may need to take medication, immunotherapy, changes in your work environment, or diet as part of your allergy treatment plan. Talk to your doctor if you have any questions about your treatment or diagnosis.
You can reduce or eliminate your allergy symptoms by having test results that identify allergens.
Skin pricking
Skin pricking is an allergy test that identifies allergens that trigger symptoms in allergic diseases.
One of the most popular allergy tests is skin pricking. This involves placing a droplet of liquid on your forearm. It may contain a substance that you are allergic to. Next, gently poke the skin underneath the drop. Within 15 minutes, you will notice a red, itchy bump if you are allergic to the substance.
Skin Prick Testing can provide information about the presence and concentration of allergens in an allergic individual. The epidermis and the non-vascular superficial dermis are contaminated with small amounts of allergens. These allergens interact with IgE that is bound to cutaneous mast cells.
Histamine and other mediators can be released in allergic patients, resulting in a visible “wheal” reaction that peaks after approximately 15 minutes.
A positive SPT test is approximately 50 percent reliable, while a negative one is around 95 percent predictive. The preferred test for allergy is skin pricking.
A positive result is one where the diameter of the wheal exceeds 3 mm. The size of the wheal reflects the severity of the allergy. However, this should be considered in relation to the individual’s age.
These wheal sizes for adults provide some insight into the allergen’s relative sensitivity and the likelihood of becoming allergic.
| Size of wheal | Clinical significance |
|---|---|
| > 15 mm | Extremely sensitive |
| 10-15 mm | Moderately sensitive |
| 5-10 mm | Mildly sensitive |
| 3 mm | Negative results |
The positive result does not necessarily mean that you have developed allergic antibodies (called IgE) to a particular food.
During Skin Prick Testing, specific IgE to allergens is detected in allergic individuals by introducing small amounts of allergens into the epidermis and non-vascular superficial dermis and interacting with specific IgE bound to cutaneous mast cells. Histamine and other mediators are released during an allergic reaction, leading to a visible wheal-and-flare reaction that peaks after about 15 minutes.
| LIST OF ALLERGENS FOR SKIN PRICK TESTING | |||
|---|---|---|---|
| Single Allergens | |||
| Mites | Meat | Vegetables | |
| Der f. | Mutton | Potato | |
| Der pt. | Chicken | Parsley | |
| Blomia t. | Beef | Spinach | |
| Insects | Pork | Soy Bean | |
| Cockroach | Duck | Spring Onion | |
| Pollen | Fish/Crustacean | Leek | |
| Locust | Cod | Cabbage | |
| Mugwort | Carp | Pear | |
| Birch | Catfish | Flours/Brans | |
| Nettle | Tuna | Rice | |
| Chrysanthemum | Scallop | Corn Flour | |
| Alder | Crab Meat | Wheat Flour | |
| Spruce | Shrimp | Buck Wheat | |
| Lamb’s Quarters | Spiny Lobster | Green Bean | |
| Goldenrod | Mussel | Milk/Egg | |
| Humulus Japonicus | Fruits/Nuts | Cow’s Milk | |
| Pine | Pineapple | Whole Egg | |
| Orchard Grass | Apple | Egg White | |
| Dandelion | Orange | Egg Yolk | |
| Corn | Banana | Spices | |
| Poplar | Mango | Cocoa | |
| Plane Tree | Strawberry | Cinnamon | |
| Short Ragweed | Peanut | Paprika | |
| Elm | Cashew Nut | Black Pepper | |
| English Plantain | Tangerine | Sesame | |
| Willow Tree | Paprika | Garlic | |
| Wheat | Peach | Others | |
| Timothy Grass | Tomato | Hay | |
| Queen Palm | Walnut | Silk | |
| Mulberry | Grape | Cotton | |
| Rape | Sunflower Seed | Latex | |
| Ryegrass | Almond | Baker’s Yeast | |
| Epithelia | Hazelnut | Control | |
| Dog Epithelia | Pistachio | A (Positive) | |
| Cat Epithelia | Pine Nut | B (Negative) | |
| Goat Epithelia | Cocoa Bean | ||
| Duck Feather | Chestnut | ||
| Feather | Macadamia Nut | ||
| Molds | Brazil Nut | ||
| Alternaria tenuis | Lupins Bean | ||
| Aspergillus f. | Pecan Nut | ||
| Botrytis c. | Pumpkin Seed | ||
| Candida albicans | |||
| Cladosporium h. | |||
| Curvularia l. | |||
| Penicillium notatum | |||
| Pullalaria pullulans | |||
| Trichophyton mentagrophytes | |||
| Mixed Allergens | |||
| Grasses | Australian Grasses | ||
| Velvet Grass | Bahia Grass | ||
| Orchard Grass | Johnson Grass | ||
| Ryegrass | Burmuda Grass | ||
| Timothy Grass | Velvet Grass | ||
| Kentucky Bluegrass | Canary Grass | ||
| Meadow Fescue | Animal Hair I | ||
| Trees I | Hamster | ||
| Alder | Dog | ||
| Hazel | Rabbit | ||
| Poplar | Cat | ||
| Elm | Guinea Pig | ||
| Willow | Moulds I | ||
| Trees II | Alternaria tenuis | ||
| Birch | Botrytis c. | ||
| Beech | Cladosporium h. | ||
| Oak | Curvularia I. | ||
| Platanus | Fusarium globosum | ||
| Mixed Grass | Helminthosporium halodes | ||
| Mugwort | Moulds II | ||
| Nettle | Aspergillus f. | ||
| Dandelion | Mucor mucedo | ||
| English Plantain | Penicillium notatum | ||
| Grasses/Cereals | Pullularia pullulans | ||
| Grasses | Rhizopus nigricans | ||
| Barley | Serpula lacrymans | ||
| Oat | Meat II | ||
| Rye | Duck | ||
| Wheat | Chicken | ||
| Turkey | |||
| Goose | |||
Food allergy testing
- Milk
- Soy
- Wheat
- Eggs
- Tree nuts (almonds, walnuts, and pecans),
- Fish
- Shellfish
- Peanuts
A food allergy test result can be confusing to someone who has not had any medical training. Food allergy tests are becoming more widely available. This means that more people will have to interpret the results themselves.
Let’s see how the scoring system works and what it means.
- Low values of 0.35 indicate a low likelihood of sensitization to the allergen.
- A value between 0.35 to 0.69 indicates doubtful significance.
- There is a possibility of obtaining values between 0.70 and 3.49.
- A higher chance is indicated by values between 3.50 and 17.49
- Very likely, values between 17.50 to 49.99 refer to.
- A very high probability is indicated by values between 50.00 and 100.00.
- High values of 100.00 are considered extremely probable.
The more severe the allergy symptoms are, the higher the number.
The Skin Prick is a non-invasive test that is painless and not invasive. This testing involves the use of needles (lancets), which only barely penetrate the skin. The prick is not painful and there is no bleeding.
Skin tests are generally more sensitive than blood tests. This means that they are more likely to detect allergies that may not be detected by a blood test. The wait time for skin tests is shorter than for blood tests, which can take up to two weeks. Results are usually delivered within 15-20 minutes.
