Skin testing is the everyday diagnostic work of an allergy practice. The AAAAI/ACAAI Joint Task Force describes prick/puncture and intracutaneous skin tests as established, reliable and cost-effective techniques for diagnosing IgE-mediated disease.[1] Patch testing is the definitive technique for allergic contact dermatitis.[1][3] This guide brings together what the practice parameters say about each test, where the parameters differ, and what a complete record should contain.
This is a clinician-level summary of published practice parameters, not patient instructions. Each statement cites its source. Where parameters differ, we say so rather than pick one cut-off.
Skin prick testing (SPT)
What it's for
- Prick/puncture tests confirm clinical sensitivity to aeroallergens, foods, some drugs and a few chemicals.[1]
- A positive SPT shows sensitization, not a diagnosis on its own. Results are read together with the history.[1][4][5] For food, NIAID notes that "the SPT alone cannot be considered diagnostic" because its positive predictive value is low.[4]
- The number and choice of tests follow the patient's age, history, environment, region, occupation and activities. Routine large panels, or routine annual testing without a clear indication, are described as "clearly not justified".[1]
- Medicare coverage language calls percutaneous testing "the usual preferred method" when immediate hypersensitivity is suspected, and requires medical supervision because of a small but significant risk of anaphylaxis.[12]
Devices and sites
- Hypodermic needles, solid-bore needles, lancets with or without a bifurcated tip, and multiple-head devices can all be used. No single device has a clear advantage, and wheal size varies between devices at both positive and negative sites.[1]
- The parameter's advice is to choose one device and train skin-test staff well in its use.[1]
- Tests go on the upper back or volar forearm. The back is more reactive than the forearm, and reactivity varies within each area. The parameter describes spacing of about 2 to 2.5 cm between allergens.[1]
- Reliability depends on the tester's skill, the instrument, skin color and reactivity that day, age, and the potency and stability of the extracts.[1]
Controls
- Positive (histamine) and negative (saline, or 50% glycerinated HSA–saline when concentrated glycerinated extracts are used) controls are placed at the same time as the allergen tests.[1]
- A 10 mg/mL histamine dihydrochloride control is the preferred positive control for SPT.[1]
- For drug testing, the positive and negative controls must read as positive and negative for the results to be valid.[2]
Reading and interpretation
- SPT reactivity peaks at 15 to 20 minutes. At that point both the wheal and the erythema (flare) diameters are recorded in millimeters and compared with the positive and negative controls.[1]
- Qualitative 0 to 4+ grades are no longer used by many clinicians, and the 2008 parameter recommends recording millimeters instead of numerical grades.[1]
- Size can be reported as mean wheal diameter, (D + d) / 2, where D is the largest diameter and d the largest diameter at right angles to it.[1]
- Positivity (2008 diagnostic parameter): a response at least 3 mm larger in diameter than the diluent control, with equivalent erythema, is required as evidence of allergen-specific IgE. A response under 3 mm generally should not be regarded as positive.[1]
- Positivity (2022 drug allergy parameter): a wheal at least 3 mm larger than the negative control, accompanied by a flare of at least 5 mm.[2]
- Common false positives include tree pollens in honeybee-venom-sensitive patients (cross-reactive carbohydrate determinants) and tree pollens not native to the area.[1]
Because criteria differ by parameter and by allergen class, a practice's written criteria should say which definition it uses, and the record should hold the millimeter values the classification was based on.[1][2][7]
What interferes with SPT
- Antihistamines suppress wheal and flare to different degrees. The 2008 parameter's general principle is to stop first- and second-generation antihistamines 2 to 3 days before testing, with named exceptions (including cetirizine, hydroxyzine, clemastine, loratadine and cyproheptadine) that suppress for longer.[1] ACAAI's patient page gives 3 to 7 days.[15]
- Doxepin may suppress reactions for as long as 6 days. H2 antagonists may cause mild suppression.[1]
- Leukotriene antagonists had negligible effects, and a short course of oral prednisone (30 mg/day for a week) did not suppress immediate skin tests.[1]
- Potent topical corticosteroids applied to a site for more than 3 weeks may suppress tests at that site.[1]
Precautions
- Sites with active dermatitis or severe dermatographism are not tested.[1]
- Specific IgE testing may be preferable with widespread skin disease, skin-test-suppressive therapy, a patient who cannot cooperate, or a history suggesting unusually high anaphylaxis risk from skin testing.[1]
- After anaphylaxis, immediate skin testing is generally delayed 4 to 6 weeks because of a possible refractory period.[8]
- Beta-blockers and ACE inhibitors were a relative contraindication in the 2008 parameter; the 2023 anaphylaxis parameter moves toward shared decision-making.[1][8]
Intradermal testing (IDT)
When it's used
- Intradermal testing identifies more patients with lower skin-test sensitivity and is used when greater sensitivity is the main goal.[1]
- It is useful for evaluating anaphylaxis, particularly to drugs such as penicillin and to Hymenoptera venom.[1] For penicillin, full-strength reagents are applied by prick first, and intradermal testing follows if those are negative.[2]
- Medicare coverage language describes IDT as usually done when percutaneous tests are negative and clinical suspicion remains strong.[14]
- Not for food. Intradermal food tests are described as potentially dangerous and overly sensitive, and are not recommended.[1] NIAID says intradermal testing should not be used to diagnose food allergy.[4]
Volumes and dilutions (as the parameters describe them)
- Small volumes of about 0.02 to 0.05 mL are injected with a 0.5 or 1.0 mL syringe.[1] The 2022 drug parameter describes injecting 0.02 mL to raise a 3 to 5 mm baseline bleb.[2]
- The starting intradermal dose is generally 100- to 1,000-fold more dilute than the concentration used for SPT.[1]
- For venom, the 2016 parameter describes starting at 0.001 to 0.01 µg/mL and increasing 10-fold until a positive or 1.0 µg/mL. A positive at or below 1.0 µg/mL indicates specific IgE.[7]
Reading
- Intradermal tests are read 10 to 15 minutes after injection, with both wheal and erythema recorded in millimeters, alongside a diluent control. The intradermal histamine control is weaker than the SPT control.[1]
- Criteria vary. The 2008 parameter notes that any reaction larger than the negative control may indicate specific IgE, and that most surveyed board-certified allergists use at least 3 mm above the negative control. The 2022 drug parameter uses a wheal at least 3 mm larger than the negative control with a flare of at least 5 mm.[1][2]
- For venom, North American and European convention is a wheal 3 to 5 mm larger than the negative control with surrounding erythema; the UK convention reads at 20 minutes.[7]
Safety
- Immediate systemic reactions are more common with intracutaneous tests than with prick tests, and screening with prick tests first is a practical way to avoid serious reactions.[1]
- Intradermal tests are usually placed on the upper arm or forearm rather than the back.[1]
- Penicillin skin testing should be done by trained staff prepared to treat the very rare case of anaphylaxis.[2]
Patch testing Supported in Medora
What it's for
- The epicutaneous patch test is the definitive technique for diagnosing allergic contact dermatitis, and it is often called the gold standard.[1][3][10]
- It is indicated in chronic, pruritic, eczematous or lichenified dermatitis when underlying or secondary allergic contact dermatitis is suspected, and it is especially important in occupational dermatitis.[1][10]
Series and application
- Patch testing uses a preloaded kit such as the T.R.U.E. Test, or individually loaded chambers following the NACDG or ACDS series, plus supplemental allergens and the patient's own products based on exposure.[3]
- The 2015 parameter notes that relying on a limited preloaded panel alone can miss clinically relevant sensitizers.[3] The ACDS Core Allergen Series was introduced in 2013 and updated in 2017 and 2020.[9]
- Patches are placed on the upper or middle back and traditionally stay occluded for 48 hours. An appropriate vehicle control is always used.[1]
- For suspected photocontact allergy, photopatch testing is used.[1][3]
Reading schedule
- Remove and read at about 48 hours, then do a second reading between days 3 and 7.[3]
- Waiting about 30 minutes after removal lets erythema from occlusion pressure or tape resolve before reading.[3]
- About three in ten relevant allergens that are negative at 48 hours turn positive by 96 hours, so 96 hours may be the best time for the second reading. A later reading after day 7 can be needed for metals, some antibiotics and topical corticosteroids.[1][3]
- Irritant reactions seen at 48 hours tend to fade by 96 hours (a "decrescendo" pattern).[1][3]
ICDRG grading
Patch tests are read and interpreted using the International Contact Dermatitis Research Group scale.[3]
| Grade | Meaning |
|---|---|
| − | Negative reaction |
| ?+ | Doubtful reaction: faint erythema only |
| + | Weak positive: nonvesicular erythema, infiltration, possibly papules |
| ++ | Strong positive: vesicular erythema, infiltration and papules |
| +++ | Extreme positive: intense erythema and infiltration, coalescing vesicles, bullous reaction |
| IR | Irritant reaction |
| NT | Not tested |
- Most misinterpretation happens in the doubtful and weak positive categories. Pustular reactions, common with metals and in atopic patients, are frequently irritant.[3]
- "Angry back" (excited skin) can produce false positives next to strong true positives.[1][3]
- When experienced dermatologists graded patch tests from photographs, their ICDRG grades differed widely, and agreement came only after collapsing grades to negative, positive and irritant.[11] Photos support documentation; the grade is the clinician's.
Relevance, medications and documentation
- The relevance of each positive result comes from the clinical and exposure history and is recorded as current (definite, probable or possible) or past.[3]
- Antihistamines do not need to be withheld for patch testing. Topical corticosteroids and calcineurin inhibitors at the test site, UV exposure and systemic immunosuppression should be avoided or reduced.[3]
- Record the grade at each reading, then the relevance of each positive.[3] Medicare coverage language describes interpretation at 48 hours and typically again at 72 or 96 hours, with reactions "systematically scored and recorded".[12]
SPT vs intradermal vs patch testing
Three tests, three different questions. Tap a card to see how each is used and recorded.
When each test is read
Wheal and erythema at peak[1]
With a diluent control[1]
Show as a table
| Skin prick (SPT) | Intradermal (IDT) | Patch | |
|---|---|---|---|
| What it answers | Immediate (IgE-mediated) sensitization | Immediate sensitization when greater sensitivity is needed | Delayed-type sensitization (allergic contact dermatitis) |
| Typical use | Aeroallergens, foods, some drugs[1] | Venom, drugs such as penicillin, after a negative or equivocal SPT; not foods[1][2] | Chronic eczematous dermatitis with suspected contact allergy[1][3] |
| When it's read | 15 to 20 minutes[1] | 10 to 15 minutes[1] | About 48 hours, then days 3 to 7[3] |
| What's recorded | Wheal and erythema in mm, with controls[1] | Wheal and erythema in mm, with controls and the dilution tested[1] | ICDRG grade at each reading, then relevance[3] |
| Visits | One | One (often the same visit, after SPT) | Usually two or three |
What a complete skin test record contains
The 2008 parameter lists the minimum contents of a skin-testing form:[1]
- The date of testing, and the name or initials of the person who performed it
- The method (prick, puncture or intracutaneous)
- Each allergen by an unambiguous common name, with the concentration tested; mixes itemized by component
- The positive control agent and concentration, and the composition of the negative control
- Positive and negative control results in millimeters
- Wheal and erythema sizes in millimeters, not 0 to 4+ grades
- Extract source, manufacturer lot number and expiration date (these may be kept in separate records)
For drug testing, the reagents used, and the step at which a test turned positive, are part of a useful record.[2] For patch testing, the grade at each reading and the relevance of each positive.[3]
Coding
Medicare billing guidance lists these codes for allergy skin and patch testing. Units are the number of tests performed, one unit per test.[13]
| Code | Test family (simplified) |
|---|---|
| 95004 | Percutaneous tests (scratch, puncture, prick) with allergenic extracts |
| 95024 | Intracutaneous (intradermal), single test, immediate type |
| 95027 | Intracutaneous (intradermal), sequential and incremental |
| 95044 | Patch or application tests |
| 95052 | Photo patch tests |
These descriptions are simplified. CMS notes that several descriptors changed in the 2024 and 2025 updates, and coverage rules differ by Medicare contractor.[12][13][14] Confirm the current AMA CPT wording and your local coverage policy before billing.
Where testing-day work piles up
Every test in the record carries several data points: the allergen, its concentration, the controls, the wheal and erythema in millimeters, who tested and when.[1] On a full panel that is a lot of transcription, and it happens while the next patient waits. The same results then have to reach the note the clinician signs. Patch testing adds readings spread over several days, each with its own grade and relevance.[3] Each hand-off, from the arm to the sheet, from the sheet to the note, is a place where a value can be retyped, delayed or lost.
For more on the documentation side, see the hidden cost of manual SPT documentation, the nurse-to-provider hand-off, the skin testing bottleneck and why skin test sign-off takes so long. Seasonal planning is covered in spring pollen testing strategies and timothy grass testing.
How Medora helps
Medora is the AI copilot built only for allergy practices, built together with Dr. Sabharwal's practice, Allergy Affiliates. On skin testing, it keeps the nurse and the clinician in charge and takes the retyping out of the day.
- PhotosThe nurse photographs the panel
- Medora draftsWheal sizes against the ruler card; unsure sites flagged
- Nurse reviewsChecks the flags, corrects, confirms
- Practice rules classifyThe practice's own grading rules
- Clinician signsResults reviewed alongside the note
Skin prick and intradermal testing
- Photos of the panel. The nurse photographs the panel, with the printed ruler card in view. Vision finds each test site by the number written beside it.
- Controls first. The histamine and saline controls come first, and the draft asks for them first.
- A draft, measured against the ruler card. Medora drafts each wheal size from the photo, measured against the printed ruler card. When it can't confirm the scale or isn't sure about a site, it flags that site for the nurse instead of guessing.
- The nurse checks what Medora flags. The nurse reviews and corrects the draft, checking the flagged sites rather than every site, and can record the remaining sites as no reaction in one confirmed step. Nothing is recorded as "no reaction" until a person confirms it.
- Flare stays with the nurse. Medora doesn't size flare for the chart; the nurse records erythema.
- The practice's own rules. The practice's grading rules classify the results. The audit trail shows how each result was made: proposed by Medora, confirmed by the nurse, signed by the clinician.
- Straight into the note. Medora Copilot has visit templates for skin testing and drafts the note for clinician review. The clinician sees the results alongside the drafted note, then reviews and signs.
Patch testing
- Medora supports the patch-testing workflow: ordering, 48-hour and Day 3–4 readings scored on the ICDRG scale, photos, and clinician sign-off.
- Photo-assisted reading of patch tests is in development.
In a 60-day pilot at Allergy Affiliates, provider sign-off per skin-test visit went from 18 minutes to 4. Read the full case study, or see how Medora fits with the rest of the visit in our guide to AI for allergy and asthma practices.
Frequently asked questions
What counts as a positive skin prick test?
The 2008 AAAAI/ACAAI diagnostic testing parameter treats a skin prick response at least 3 mm larger in diameter than the diluent (negative) control, with equivalent erythema, as evidence of allergen-specific IgE. The 2022 drug allergy parameter defines a positive drug skin test as a wheal at least 3 mm larger than the negative control with a flare of at least 5 mm. A positive test shows sensitization; it has to be read together with the clinical history.[1][2]
When is intradermal testing used instead of skin prick testing?
Intradermal testing is used when greater sensitivity is the main goal, usually after a negative or equivocal prick test. The practice parameters describe it as useful for Hymenoptera venom and drugs such as penicillin. It is not recommended for diagnosing food allergy.[1][2][4]
When are skin prick tests and intradermal tests read?
Per the 2008 practice parameter, prick/puncture tests peak at 15 to 20 minutes and intradermal tests are read at 10 to 15 minutes. Both wheal and erythema are recorded in millimeters and compared with the positive (histamine) and negative controls.[1]
How are patch tests graded?
Patch tests are read and graded with the International Contact Dermatitis Research Group (ICDRG) scale: negative, doubtful (?+), weak positive (+), strong positive (++), extreme positive (+++), irritant reaction (IR) and not tested (NT). Each positive is then assessed for clinical relevance.[3]
When are patch tests read?
The 2015 contact dermatitis parameter recommends removing and reading the patches at about 48 hours, with a second reading between days 3 and 7. A second reading around 96 hours may be best, and a later reading after day 7 can be needed for metals, some antibiotics and topical corticosteroids.[3]
What should a complete skin test record contain?
The 2008 parameter lists the date, who performed the test, the method, each allergen by common name with its concentration, the positive and negative control agents and their results, and wheal and erythema sizes in millimeters rather than 0 to 4+ grades. Extract source, lot number and expiration date may be kept in separate records.[1]
Which medications interfere with skin testing?
Antihistamines suppress wheal and flare to different degrees, so the 2008 parameter advises stopping them before testing, with some needing a longer washout. Doxepin can suppress reactions for up to about 6 days. Leukotriene antagonists and short courses of oral corticosteroids generally do not suppress immediate skin tests. For patch testing, antihistamines do not need to be withheld, but topical corticosteroids at the test site and systemic immunosuppression do matter.[1][3]
Which CPT codes are used for allergy skin and patch testing?
Medicare billing guidance lists 95004 for percutaneous (scratch, puncture or prick) tests, 95024 for single intradermal tests, 95027 for sequential and incremental intradermal tests, and 95044 for patch or application tests, each billed per test. Descriptors change over time, so practices should confirm current AMA CPT wording and their local coverage rules.[13]
Does Medora read skin tests?
Medora drafts wheal sizes from the photo against the printed ruler card and flags anything it isn't sure of; the nurse reviews and corrects the draft, and the clinician signs. Medora doesn't measure flare and never records 'no reaction' on its own.
Does Medora support patch testing?
Yes. Medora supports the patch-testing workflow: ordering, 48-hour and Day 3–4 readings scored on the ICDRG scale, photos, and clinician sign-off. Photo-assisted reading of patch tests is in development.
Sources
Last reviewed September 29, 2026. Summaries paraphrase the cited documents; consult the originals for clinical decisions.
- Bernstein IL, Li JT, Bernstein DI, et al. Allergy diagnostic testing: an updated practice parameter. Ann Allergy Asthma Immunol. 2008;100(3 Suppl 3):S1–S148. AAAAI PDF
- Khan DA, Banerji A, Blumenthal KG, et al. Drug allergy: a 2022 practice parameter update. J Allergy Clin Immunol. 2022;150(6):1333–1393. AAAAI PDF
- Fonacier L, Bernstein DI, Pacheco K, et al. Contact dermatitis: a practice parameter—update 2015. J Allergy Clin Immunol Pract. 2015;3(3 Suppl):S1–S39. AAAAI PDF
- NIAID-Sponsored Expert Panel. Guidelines for the diagnosis and management of food allergy in the United States. J Allergy Clin Immunol. 2010;126(6 Suppl):S1–S58. PMC
- Sampson HA, Aceves S, Bock SA, et al. Food allergy: a practice parameter update—2014. J Allergy Clin Immunol. 2014;134(5):1016–1025. AAAAI PDF
- Greenhawt M, Shaker M, Wang J, et al. Peanut allergy diagnosis: a 2020 practice parameter update. J Allergy Clin Immunol. 2020. AAAAI PDF (background)
- Golden DBK, Demain J, Freeman T, et al. Stinging insect hypersensitivity: a practice parameter update 2016. Ann Allergy Asthma Immunol. 2017;118(1):28–54. AAAAI PDF
- Golden DBK, Wang J, Waserman S, et al. Anaphylaxis: a 2023 practice parameter update. Ann Allergy Asthma Immunol. 2024;132(2):124–176. AAAAI PDF
- Schalock PC, Dunnick CA, Nedorost S, et al. American Contact Dermatitis Society Core Allergen Series: 2020 update. Dermatitis. 2020;31(5):279–282. PubMed
- Fonacier L. A practical guide to patch testing. J Allergy Clin Immunol Pract. 2015;3(5):669–675. PubMed
- Ivens U, Serup J, O'goshi K. Allergy patch test reading from photographic images: disagreement on ICDRG grading but agreement on simplified tripartite reading. Skin Res Technol. 2007;13(1):110–113. PubMed
- CMS Medicare Coverage Database. LCD: Allergy Testing (L36402), Wisconsin Physicians Service. CMS
- CMS Medicare Coverage Database. Billing and Coding: Allergy Testing (A57473). CMS
- CMS Medicare Coverage Database. LCD: Allergy Testing (L34313), Noridian. CMS
- American College of Allergy, Asthma & Immunology. Allergy testing. ACAAI