It is a detailed presentation about patch test. It includes indication, contraindications, adverse reaction, relevance.

1. Patch test

2. Introduction :
• Epicutaneous patch testing is the gold standard method for the diagnosis of allergic
contact dermatitis.
• Patch testing helps identify which substances may be causing a delayed-type allergic
reaction in a patient, and may identify allergens not identified by blood testing or skin
prick testing.
• A patch test relies on the principle of a type IV hypersensitivity reaction.
• The use of patch testing to diagnose ACD was first developed by Josef Jadassohn in
1895.
• More than 3,000 chemicals are known to cause ACD.
• ACD is an immunological reaction that occurs in genetically susceptible people who
have been previously sensitized to an allergen. This is in contrast to ICD, which can
occur in any person if the amount and duration of irritant exposure are sufficient to
cause direct epidermal keratinocyte damage.

3. Pathogenesis :

4. Relevance :
Relevance is determined by exposure to the positive allergen(s), and is rated as :
• Definite
• Probable
• Possible
• Past
• Unknown
• For an allergen to have definite relevance, the product the patient is exposed to must be
tested and also be positive in addition to the test allergen.
• The confirmation of relevance will occur after the patient has avoided exposure to the
chemical and after he has noticed that the improvement or clearance of his dermatitis is
directly related to this avoidance. This outcome usually occurs within four to six weeks after
stopping the exposure to the chemical.

5. • If all patch tests are negative, the allergic reaction is probably not due to an allergic
reaction to a contactant. It is possible, that the patient was not tested for other chemicals
that can produce allergic reactions on rare occasions. If the suspicion is high in spite of
negative patch testing, further investigation might be required.
• A positive patch test might not explain the present skin problem, since the test only
indicates that the individual became allergic during encounters with that chemical at some
point in their life. Relevance, therefore, has to be established by determining the causal
relationship between the positive test and the eczema.

6. The top allergens are (NACDG 2005-2006):
• Nickel sulfate (19.0%)
• Myroxylon pereirae (Balsam of Peru 11.9%)
• Fragrance mix I (11.5%)
• Quaternium15 (10.3%)
• Neomycin (10.0%)
• Bacitracin (9.2%)
• Formaldehyde (9.0%)
• Cobalt chloride(8.4%)
• Methyldibromoglutaronitrile/phenoxyethanol (5.8%)
• P-phenylenediamine (5.0%)
• Potassium dichromate (4.8%)
• Carba mix (3.9%)
• Thiuram mix (3.9%)
• Diazolidinyl urea (3.7%)
• 2-bromo-2-nitropropane-1,3-diol (3.4%).

7. Patch test units :
• Chambers made of aluminium and plastic with diameters of 10–15 mm and volume of
15–100 microliters have been introduced.
• The Finn chamber is presently the most commonly used test unit. It consists of stiff
aluminium and has a diameter of 8 mm and depth of 0.5 mm. Its particular advantage is
its tight apposition to the skin thus localizing the reaction to the test site, use of a porous
tape, and a small area required for patch testing.
• However, even with the correct techniques, small amounts of test material may diffuse
slightly beyond the site of the patch test.
• Occasionally, metal salts like mercury, cobalt, and nickel interact with aluminium, but this
effect can be eliminated by plastic coated Finn chambers.

8. Procedure : (Standard Patch test)
• Application of the patch tests takes about half an hour, though many times the overall
appointment time is longer as the provider will take an extensive history.
• Tiny quantities of 25 to ~150 materials (allergens) in individual square plastic or round
aluminium chambers are applied to the upper back. They are kept in place with
special hypoallergenic adhesive tape.
• The patches stay in place undisturbed for at least 48 hours.
• At the second appointment, usually 48 hours later, the patches are removed. Sometimes
additional patches are applied.
• The back is marked with an indelible black felt tip pen or other suitable marker to identify
the test sites, and a preliminary reading is done.
• These marks must be visible at the third appointment, usually 24–48 hours later (72–96
hours after application). In some cases, a reading at 7 days may be requested, especially if
a special metal series is tested.

9. Baseline/standard test series of allergens for patch test :
• The European Standard Series
• International Standard
• Belgium Standard
• Finnish Standard
• GIRDCA Series
• Korean Standard
• North American Series
• Swedish Standard
• Hungarian Standard.

10. Base line series of patch test
allergens
Using IQ chambers Applying liquid for patch test

11. T.R.U.E. Test (Thin-Layer Rapid Use Epicutaneous Test) :
• In 1995, the United States Food and Drug Administration (FDA) approved the first ready-
to-use patch testing system i.e. TRUE test.
• The introduction of TRUE Test suddenly made patch testing much more convenient. In a
busy clinical practice, the TRUE Test is certainly a good starting point when addressing the
need for patch testing.
• The approval of TRUE Test made patch testing much more convenient for those either
converting over to the TRUE Test or just starting to patch test.
• The original TRUE Test consisted of 23 allergens and one control that could be applied to
the patient's back with little additional preparation.
• In 2007, the TRUE Test was expanded to include five additional allergens. Currently, there
are plans to expand the TRUE Test even further to include three full panels (35 allergens
and one control).

12. • Although patch testing beyond the TRUE Test does not have FDA approval, many
dermatology referral centers routinely use an expanded allergen series of 50 to 80
allergens, such as the NACDG Screening Series.
• Currently using the TRUE Test to increase sensitivity of patch testing for their patients is
to be knowledgeable of which allergens are most likely to be missed by the TRUE Test.
• Adding another 10 to 30 of the most common allergens (either through a standard
additional series or customized to the patient) can increase diagnostic yield of the patch
test for the patient.
Indication :
Diagnosis of allergic 8 contact dermatitis (ACD) in persons 6 years of age and older
whose history suggests sensitivity to one or 9 more of the 35 allergens and allergen
mixes included on the T.R.U.E. TEST panels.

13. T.R.U.E. TEST
contains three adhesive
panels consisting of 35
allergen and allergen
mix patches and a
negative control.

14. Vehicles :
• Polyester patches coated with allergens in a hydrophilic vehicle in TRUE test.
• Standard vehicle is white petrolatum due to its refined nature and almost negligible
sensitizing potential.
• Petrolatum is highly lipophilic and most allergens are hydrophilic. The bioavailability of
such allergens from petrolatum seems to be low. Thus recently the role of petrolatum
as the most suitable vehicle has been questioned.
• Softisan, a hydrophilic lanolin substitute, and Plastibase have been suggested as
alternative vehicles.

17. Timing of Test Readings :
• Schedule patients to return approximately 48 hours after patch test application to have
the panels removed.
• Prior to removal of the panels, use a medical marking pen to remark the notches found
on the 61 panels.
• The patch test reaction on the patient’s skin may be evaluated at 48 hours, but an
additional 62 reading(s) at 72 and/or 96 hours is necessary.
• Late positive reactions may occur 7 to 21 days after 63 application of the panels.
Contraindications :
• Do not apply to skin of patients with a history of severe allergic reaction 33 (systemic
and/or local) to any of the allergen components or inactive 34 substances of T.R.U.E. TEST.
• Do not apply to skin that is injured or inflamed.

19. Interpretation :

20. False Negatives :
• False negative results may be due to insufficient patch contact with the skin and/or
premature evaluation of the test. Repeat testing may be indicated.
• The effect of repetitive testing with T.R.U.E. TEST is unknown.
• The substance is small, the concentration of the allergen is low, or it is poorly absorbed or
insufficiently released.
• Refractory state, which sometimes occurs immediately after a very severe allergic contact
dermatitis and the patient fails to respond to the dilute allergens but reacts when
retested several weeks later. A similar diminution of reactivity may occur in patients who
are on oral prednisolone in daily doses of more than 15–20 mg.

21. False Positives :
• A false positive result may occur when an irritant reaction cannot be differentiated from an
allergic reaction.
• A positive test reaction should meet the criteria for an allergic reaction. If an irritant
reaction cannot be distinguished from a true positive reaction or if a doubtful reaction is
present, a retest may be considered.
• The effect of repetitive testing with T.R.U.E. TEST is unknown.
Hyperreactive skin:
• Also called excited skin syndrome, (ESS), angry back syndrome, crazy back and status
eczematicus
• It occurs in patients presenting with multiple concomitant positive reactions to diagnostic
patch tests for allergic contact dermatitis, in whom a single repeated challenge reveals
some of them to be non-reproducible.
• Strong positive reactions, adhesive tape dermatitis, and even hand eczema (localized
dermatitis) may induce skin
• hyperirritability. It is a major cause of false positive nonrelevant patch test reactions.

22. Artifact:
• Sometimes a patient seeking compensation may try to simulate a positive reaction by
scratching or otherwise irritating the skin.
Precautions :
• Do not expose your back to the sun for four weeks before your patch tests
• Wear old clothing; felt tip pen marks can stain clothes
• Do not swim, rub, or exercise, as the patches may come off
• Keep the back dry, so no baths, showers or unnecessary sweating
• Arrange for someone to remark the test sites with indelible felt tip marker
• If excessive body hair exists at the test site, remove with an electric 27 shaver (do not
use razors).
• Very oily skin may be cleaned with mild soap and water prior to testing.

23. Adverse reaction :
• Positive patch test results are small areas of active eczema/dermatitis. They will be itchy
and may require treatment with topical steroid.
• Occasionally patch test reactions persist for several weeks.
• Patch tests may provoke other areas of dermatitis to recur or to appear for the first time.
• Although hypoallergenic tape is used, occasionally people react to all areas in contact
with the tape. (Tape reaction).
• An 'angry back' reaction may arise, particularly in a patient with active dermatitis at the
time of testing, or in someone who has multiple positive reactions. 'Angry back' refers to
false positives to many or all of the tested allergens.
• Rarely, sensitization to a new allergen may occur as a result of the test – this is revealed
as a reaction occurring around 10 days after the test was applied.

24. • Persistent positive reaction: A patch test reaction normally disappears in 1 to 2 weeks,
but it may remain for longer than 1 month; persistence up to 8 months has been
reported.
• Anaphylaxis: Though rare, formaldehyde has been suspected as the cause in a few
cases of anaphylaxis during patch testing.
• Hypo / hyperpigmentation

25. Angry back Tape dermatitis/ reaction

26. Advantages :
• It meets almost all pre-requisites of the most suitable test method due to the
least possible time consumed in application of the patches
• Uniform distribution and release of antigen
• Less amount of antigen required
• Minimum irritant reactions
• Easy storage
• Stability

27. Repeated Open Application Tests (ROAT) :
• The substances are applied twice daily on at least 5 cm2 area on the upper arm for 7
days or until a positive eczematous reaction develops.
• This test may be used to help determine the relevance of doubtful positive patch-test
reactions to preparations in which the suspected allergen is present in a low
concentration.
Photo patch Testing :
• Antigens are applied in duplicate parallel to each other and covered with an opaque
material. The patches are removed on day 2 and read as usual.
• One set is then irradiated with UVA (50% of the minimum erythema dose). When an
allergic reaction occurs only on the irradiated side and not on the control side, it is
recorded as a positive photoallergic patch test.
• Phototest series have been developed in various countries. It is important to distinguish
phototoxic from photoallergic reactions.

28. Thank you