CDT Allergy Testing & Patch Testing 2 — Questions and Answers
Question 1: According to the ICDRG grading system, what does a '++' reaction indicate?
- Doubtful reaction with faint erythema only
- Weak positive with erythema and mild infiltration
- Strong positive with erythema, infiltration, and vesicles (Correct answer)
- Extreme positive reaction with bullae
Correct answer: Strong positive with erythema, infiltration, and vesicles
In the ICDRG scale, '++' (strong positive) indicates erythema, infiltration, papules, and vesicles at the patch test site.
Question 2: A '?' (doubtful/questionable) reaction in patch testing is characterized by:
- Bullae and ulceration at the test site
- Faint macular erythema without infiltration (Correct answer)
- Erythema with visible vesicles
- Strong papular infiltration
Correct answer: Faint macular erythema without infiltration
A doubtful or questionable reaction shows only faint macular erythema without any infiltration and is not considered a definitive positive result.
Question 3: What key feature differentiates an irritant reaction from a true allergic reaction on patch testing over time?
- Irritant reactions cause systemic symptoms while allergic reactions remain localized
- Irritant reactions fade by the final reading while allergic reactions persist or worsen (Correct answer)
- Irritant reactions always produce vesicles while allergic reactions cause only erythema
- Irritant reactions occur exclusively with metal allergens
Correct answer: Irritant reactions fade by the final reading while allergic reactions persist or worsen
Irritant reactions typically diminish in intensity between the 48-hour and 72–96 hour readings, whereas true allergic reactions persist or increase.
Question 4: When is the final reading of a patch test typically performed?
- 24 hours after application
- 48 hours after application
- 72–96 hours after application (Correct answer)
- 7 days after application
Correct answer: 72–96 hours after application
The final reading is performed at 72–96 hours to allow differentiation between true allergic and irritant reactions that may look similar at 48 hours.
Question 5: What is 'excited skin syndrome' (angry back) in patch testing?
- Patient anxiety causing skin flushing during application
- False-positive reactions caused by strongly positive nearby test sites (Correct answer)
- An anaphylactic reaction requiring emergency epinephrine
- Multiple negative reactions occurring on a highly sensitive patient
Correct answer: False-positive reactions caused by strongly positive nearby test sites
Angry back syndrome occurs when a strong nearby positive reaction on the test panel influences adjacent sites, producing false-positive results in neighboring allergens.
Question 6: After identifying a positive patch test allergen, what is the most critical next clinical step?
- Prescribe systemic corticosteroids immediately
- Correlate the positive result with the patient's clinical history and exposure (Correct answer)
- Repeat the entire patch test series to confirm
- Report the allergen reaction to the FDA
Correct answer: Correlate the positive result with the patient's clinical history and exposure
A positive patch test must be correlated with the patient's clinical history and actual allergen exposure to confirm relevance before making treatment or avoidance recommendations.
Question 7: Which grade in the ICDRG system represents a weak positive patch test reaction?
- ? (doubtful)
- IR (irritant reaction)
- + (weak positive) (Correct answer)
- ++ (strong positive)
Correct answer: + (weak positive)
A single '+' in the ICDRG grading system represents a weak positive reaction showing non-vesicular erythema and palpable infiltration.
CDT Allergy Testing & Patch Testing 2
According to the ICDRG grading system, what does a '++' reaction indicate?