Use of patch testing for identifying allergen causing chronic urticaria

Kaushal K Verma

 Department of Dermatology and Venereology, All India Institute of Medical Sciences, New Delhi, India,

Correspondence Address:
Kaushal K Verma
Advisor Government of India, B. P. Koirala Institute of Health Sciences, Dharan, Nepal

Sir,

I read with interest the article by Sharma AD titled "Use of patch testing for identifying allergen causing chronic urticaria". ^[1] Contact allergens are one of the etiological agents in chronic urticaria in some of the patients. In this study the author has suggested the role of patch test in etiological diagnosis of chronic urticaria. He found 11 of 57 (19%) patients showing positive patch test to various ISS allergens. In a study by Li et al , ^[2] 52.40% of their patients of suspected non-atopic chronic urticaria showed positive patch test reaction to various allergens of their standard series. However none of these were considered to be relevant, because it is well known that patients with allergic skin diseases are prone to develop sensitivities to various allergens which are demonstrable on patch test. In the present study the relevance of these positive patch test was not established which is important before one could implicate a particular allergen as a cause of chronic urticaria. Seven of their patients were patch test positive to nickel and 2 to balsum of Peru, the two common sensitizers found in various substances of day today use (including foods containing nickel) which could cause occult sensitivity in many individuals. These substances may have caused occult sensitivity in some of these patients of chronic urticaria as well in this study which were picked up on patch test. The study lacks comparison with age matched healthy controls from the same population which could have given patch test outcomes in that healthy population. Also the other potential causes of chronic urticaria like food, aero-allergens, auto-antibodies etc. were not looked for, investigated and ruled out. Neither there are details of how common allergen like nickel which is so ubiquitous, was avoided which caused remission in majority of his patch test positive patients. The possibility of spontaneous remission in some of these patients cannot be ruled out with certainty. There is no mention of controlled challenge/provocation test (possibly not done) which is important for confirmation. ^[3] Statistical analysis of data is also lacking to determine the statistical significance of the study results. There is no doubt that patch test is a safe, simple and inexpensive test, however its usefulness in etiological diagnosis of chronic urticaria seems to be of limited value so far.

1.	Sharma AD. Use of patch testing for identifying allergen causing chronic urticaria. Indian J Dermatol Venereol Leprol 2008;74:114-7. [Google Scholar]
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