Allergy Testing: Types, What to Expect and Results

What is allergy testing and why get it?

Allergy testing is how a doctor confirms which allergens your immune system reacts to — pollen, dust mites, pet dander, mold, foods, insect venom or medicines. Your symptoms and history point to likely culprits; testing narrows them down for certain.

Knowing your exact triggers is worth it because it makes everything that follows more effective: you can focus your avoidance efforts where they matter, choose the right treatment, and decide whether immunotherapy (allergy shots or tablets) could help. It's especially valuable when symptoms are hard to control, year-round, or when a food or venom allergy is suspected. Most testing is done or overseen by a board-certified allergist.

Types of allergy tests

There are several tests, each suited to different situations. Here's how they compare.

The skin prick and blood tests are by far the most common for everyday allergies like hay fever; the others are used in specific situations.

Skin prick vs. blood test: which is right?

Neither is simply "better" — they suit different people and situations.

Doctors sometimes use both together to build a clearer picture. The right choice depends on your history, skin, medicines and which allergies are suspected — an allergist will guide you.

What to expect during the test

Allergy testing is quick and generally well tolerated. For a skin prick test, a nurse places small drops of different allergen extracts on your forearm or back, then lightly pricks the skin through each drop with a tiny lancet — more of a scratch than a needle. If you're sensitive, a raised, itchy bump like a mosquito bite appears within about 15–20 minutes. Positive and negative control drops are included to check the test is working.

A blood test is simply a standard blood draw that takes a few minutes; the sample goes to a lab. Neither test is particularly painful — skin testing may cause temporary itching and redness that settles within a couple of hours. Because a serious reaction is possible (though rare), skin tests and food challenges are done in a medical setting with emergency treatment on hand.

How to prepare

The main thing to know: antihistamines can block a skin test and cause a false negative.

• Stop antihistamines several days before a skin prick test — your provider will tell you exactly which medicines (including some cold and sleep products) to pause and for how long.
• Keep taking asthma and other prescribed medicines unless told otherwise.
• A blood test needs no special preparation — antihistamines don't affect it, which is one reason it's used when you can't stop them.
• Bring a symptom history: when reactions happen, what seems to trigger them, and any suspected foods.

Which medicines interfere, and for how long

Antihistamines suppress the skin reaction the test is trying to produce, so taking one can turn a real allergy into a negative result. Cleveland Clinic describes stopping antihistamines three to seven days before a skin test. The exact window depends on the medicine and on your clinic, which is why the instruction you are given at booking overrides any general guide, including this one.

This is also why the controls matter. A skin test includes a positive control (histamine, which should produce a bump in everyone) and a negative control (a neutral liquid, which should not). If the positive control stays flat, an antihistamine is probably still in your system and the whole test may need repeating. More detail in our skin prick test guide.

Understanding your results

This is the part people most often misread: a positive test means sensitization, not automatically an allergy. It shows your immune system has made antibodies to an allergen — but plenty of sensitized people have no symptoms at all. That's why a result only means something when it matches your real-world reactions.

Borderline or unclear results — especially for foods — are often settled with a supervised oral food challenge, the most definitive test.

What the numbers on a blood test do and do not mean

An IgE number is a measurement, not a verdict. Two different results often get confused on a lab report:

• Total IgE measures all the IgE antibody in your blood. MedlinePlus notes that a high total IgE suggests allergy but does not identify which allergen or how serious it is. It can also rise for reasons that have nothing to do with allergy.
• Specific IgE measures antibody to one named allergen — birch pollen, peanut, cat. This is the number that can be matched to your history.

A higher number does not mean a more dangerous reaction. MedlinePlus states plainly that the level does not predict how serious an allergy may be. The same is true of a skin test: a larger bump is not a warning of a worse reaction, and a small one does not rule out a serious one. What raises or lowers the odds that a result is clinically real is how well it fits your actual symptoms.

False positives are common enough to expect. MedlinePlus notes results can indicate an allergy you do not have, and that recent food intake, smoking and parasitic infection can raise IgE without any allergy being present. This is the single biggest reason to have results interpreted rather than read off a portal. Our allergy blood test guide goes through a report line by line.

How accurate is allergy testing — and what does it cost?

No allergy test is perfect, which is why results are always read alongside your history. Skin tests can give false positives — showing sensitivity to something that doesn't actually bother you — and are less reliable on skin with severe eczema. They can also give false negatives if you didn't stop antihistamines. Blood tests avoid the antihistamine problem but can be slightly less sensitive. Used together with your symptom story, though, they're a reliable way to identify triggers.

Cost varies widely by test type, how many allergens are checked, and your insurance. Many plans cover testing when it's medically indicated, but it's worth checking your coverage and any out-of-pocket costs with your insurer beforehand.

Allergy testing for children

Children can be tested at almost any age when symptoms warrant it. Skin prick testing is generally suitable from around six months, while blood tests can be slightly less accurate in very young children. The decision to test should be guided by your child's symptoms, not age alone.

Because children can outgrow some allergies — particularly certain food allergies — periodic retesting is often used to track changes over time. A pediatric allergist can advise on timing. More in allergies in children.

Allergy tests to avoid

Not every "allergy test" advertised online is legitimate. Major allergy organisations advise against several unproven methods, which can waste money and lead to unnecessary, even harmful, food restrictions:

• IgG or "food sensitivity" blood tests — IgG antibodies reflect exposure, not allergy, and aren't a valid test for food allergy or intolerance.
• Hair analysis — hair contains no useful information about allergies.
• Applied kinesiology (muscle testing), "electrodermal" and cytotoxic tests — no scientific basis.

Stick to validated testing ordered and interpreted by a board-certified allergist. If a test promises to diagnose dozens of "sensitivities" from a home kit, be sceptical.

The professional position on this is unusually blunt. The American Academy of Allergy, Asthma & Immunology says of IgG food panels that the test "has never been scientifically proven to be able to accomplish what it reports to do," and that the presence of IgG is likely a normal response to eating a food — higher IgG4 levels may even be associated with tolerance of that food rather than a problem with it. AAAAI recommends against using IgG testing to diagnose food allergy, intolerance or "sensitivity."

There is a second, subtler trap: ordering too much of a legitimate test. AAAAI's Choosing Wisely guidance advises against an indiscriminate battery of IgE tests, because screening for dozens of allergens you have no history of reacting to produces clinically irrelevant positives, and those positives lead to food avoidance that was never necessary. Testing works best when it is aimed at a specific question raised by your symptoms — which is also why a targeted panel chosen by an allergist beats a broad one chosen by a website. See at-home allergy test kits for how the direct-to-consumer versions compare.

Testing for drug and insect-sting allergy

These two sit apart from everyday hay-fever testing, because getting the answer wrong has larger consequences in both directions.

Drug allergy. A label in your medical record such as "penicillin allergy" changes which antibiotics you can be given for the rest of your life, often pushing you toward broader, costlier alternatives. Many of those labels turn out to be wrong — a childhood rash, a stomach upset, or a reaction that has since faded. Formal evaluation, which may combine skin testing with a supervised challenge, can remove an inaccurate label. Read penicillin allergy and drug allergy.

Insect venom. After a serious sting reaction, testing identifies which venom you react to and opens the door to venom immunotherapy, which is highly effective at reducing the risk of another severe reaction. Skin testing for venom sometimes needs the more sensitive intradermal method when the prick test is negative but the history is convincing. See insect sting allergy.

Both are specialist evaluations rather than something to arrange from a home kit, and both are usually done where emergency treatment is immediately available.

After your results: what happens next

A confirmed diagnosis turns guesswork into a plan. Depending on what's found, your doctor may recommend targeted avoidance of your triggers, the right allergy medicine for your symptoms, and — for suitable candidates — immunotherapy (allergy shots or under-the-tongue tablets) that can reduce your reaction over time. If a food or venom allergy carries a risk of a severe reaction, you may be prescribed an epinephrine auto-injector and an action plan. See the full picture in our treatment & relief guide.

Go deeper on each step

Each part of the testing process has its own guide. Use this to jump to whichever question you are actually at.

When to get tested

Consider allergy testing if your symptoms are hard to control, last most of the year, disrupt your sleep or daily life, or if you don't know what's triggering them. Testing is also important after any suspected food, medicine or insect-sting reaction, and for anyone considering immunotherapy. See when to see a doctor for allergies.

Allergy testing: frequently asked questions

How we create and review this guide

This guide is written for a general audience using patient-education material from the authoritative sources below, not blogs or forums:

1. American Academy of Allergy, Asthma & Immunology (AAAAI)
2. American College of Allergy, Asthma & Immunology (ACAAI)
3. Cleveland Clinic
4. Mayo Clinic
5. U.S. National Library of Medicine (MedlinePlus)

Sources for the specific figures on this page

1. Cleveland Clinic. Allergy Testing (opens in a new tab). Stopping antihistamines three to seven days before a skin test, continuing asthma medicine, wheals appearing within about 15 minutes, patch tests taking several days, laboratory blood results taking a week or longer, and anaphylaxis as a rare risk managed with epinephrine on hand.
2. MedlinePlus, U.S. National Library of Medicine. Allergy Blood Test (opens in a new tab). The difference between total and specific IgE, the statement that the level does not predict how serious an allergy may be, and false positives including those caused by recent food intake, smoking or parasitic infection.
3. American Academy of Allergy, Asthma & Immunology. The myth of IgG food panel testing (opens in a new tab). IgG food panel testing never having been scientifically proven to do what it reports, IgG likely representing a normal response to food exposure with higher IgG4 possibly associated with tolerance, and the recommendation against using IgG testing to diagnose food allergy or intolerance.
4. American Academy of Allergy, Asthma & Immunology. Choosing Wisely recommendations (opens in a new tab). The recommendation against performing unproven diagnostic tests such as IgG testing or an indiscriminate battery of IgE tests in the evaluation of allergy.
5. Small P, Kim H. Allergic rhinitis (opens in a new tab). Allergy, Asthma & Clinical Immunology 2011. The wheal-and-flare response appearing within 15 to 20 minutes, and skin prick testing being generally more sensitive and more cost-effective than allergen-specific IgE blood testing while giving immediate results.

Medical disclaimer: This guide is for general education and isn't a substitute for personalized medical advice. Allergy testing should be ordered and interpreted by a qualified healthcare professional.

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