A Patch Testing Initiative for the Investigation of Allergic Contact Dermatitis in a UK Allergy Practice: A Retrospective Study.

BACKGROUND: Patch testing is the gold standard diagnostic tool for investigating allergic contact dermatitis (ACD). In the United Kingdom, patch testing has been historically confined to the dermatologist's office. Furthermore, detailed studies on patch testing by allergists are significantly underrepresented at the international level. OBJECTIVE: The objective of this study was to undertake a comprehensive evaluation of a patch testing initiative from an allergy practice; we report on various patient characteristics, prevalence and relevance data, in addition to immediate hypersensitivity testing. METHODS: We undertook a retrospective analysis of 156 patients suspected of having contact dermatitis seen in our UK allergy practice between October 2016 and April 2018. RESULTS: Of the 156 patients patch tested (mean age 36.9 years, female 88%, white ethnicity 71.8%, atopy 68.6%), ACD was diagnosed overall in 49% of the cohort and ACD of current relevance was assigned to 31%. Our extended British standard series alone detected the responsible allergen in 87% of patients, and the remaining 13% were detected from supplementary or own material testing alone. Most prevalent contact allergens were nickel (28.2%), p-phenylenediamine (8.3%), cobalt (8.3%), methylisothiazolinone (5.8%), and hydroperoxides of linalool (4.5%) and limonene (4.5%). A history of occupationally related dermatitis (P = .004) and initial (pretest) diagnosis of ACD (P < .001) were both significantly associated with relevant positive patch test reactions (atopy status was not associated P > .05). CONCLUSIONS: ACD was detected in almost 50% of assessed patients, and we highlight the importance of assessing relevance. Hydroperoxides of limonene and linalool are notable additions to the prevalence data. Patch testing should be incorporated into more allergy practices, although availability of training is a limiting factor.

Beta-lactam allergy in Chinese patients and factors predicting genuine allergy.

INTRODUCTION: Beta-lactams (BL) are the most frequently reported drug allergy, but the vast majority of patients are found not to be genuinely allergic after evaluation. Few studies have investigated the clinical predictors of genuine BL allergy, and the prevalence in hospitalized Chinese patients is unknown. METHODS: Patients admitted to a tertiary hospital in Hong Kong (HK) were analyzed to identify the prevalence and factors associated with the presence of BL allergy labels among hospitalized Chinese patients. A combined cohort of patients having completed allergy investigation for suspected BL allergies in the United Kingdom (UK) and HK were analyzed to identify predictors of genuine allergy. RESULTS: The prevalence of BL allergy labels in hospitalized HK Chinese was 5%, which was associated with female gender and concomitant non-BL antibiotic allergy labels. The rate of genuine BL allergy patients referred for suspected allergies in the UK and HK cohort was only 14%. History of anaphylaxis and interval of less than a year since the index reaction were independent clinical predictors of genuine BL allergy. The negative predictive value of penicillin skin testing was 90%, confirming the need for drug provocation testing after negative skin testing. There was a high rate of confirmed piperacillin-tazobactam allergy. DISCUSSION: The estimated true prevalence of genuine BL allergy in hospitalized HK Chinese is around 0.5%. This high rate of BL mislabeling highlights the need for comprehensive allergy evaluation and screening. History of anaphylaxis and duration since the index reaction are important predictors of genuine allergy. Piperacillin-tazobactam allergy may pose a unique challenge in this population with a high prevalence of suspected allergies, surging antibiotic resistance, and lack of testing available.

Identifying Low-Risk Beta-Lactam Allergy Patients in a UK Tertiary Centre.

BACKGROUND: There are marked geographical as well as temporal differences in patient sensitization profiles to ß-lactams (BL). OBJECTIVE: To determine the utility of skin test reagents and identify a cohort of patients where skin testing can be safely omitted in a cohort of patients referred to a UK tertiary referral center. METHODS: A retrospective study of the clinical characteristics of 1092 patients referred for BL allergy testing was analyzed using multivariate regression analysis. The effectiveness of skin test reagents was also evaluated. RESULTS: Multivariate logistic regression identified that a history of anaphylaxis (odds ratio [OR] 10.98, P = .001) and the patients' recall of the index drug (apart from ampicillin and meropenem, OR 3.51-12.43, P < .05) were independent predictors of type I BL allergic status and a time of less than 1 year elapsed since index reaction significantly increasing the odds of a patient with a history of anaphylaxis, having a type I BL allergy (OR 38.66, P = .003). An absence of anaphylactic severity, unknown name of the index drug and a reaction occurring more than 1 year before testing, has a negative predictive value (NPV) of 98.4%, which was similar to the NPV of skin testing of 98.9% for type I BL allergy. The NPV of skin testing with benzylpenicillin + amoxicillin ± index BL was similar with (98.9%) or without (98.1%) the use of benzylpenicillin polylysine and minor determinant for type I BL allergy. CONCLUSION: We identified a "low risk" cohort of patients where the history is of similar reliability to skin testing in predicting nonallergic status for BL allergy.

Steroid Allergy: Clinical Features and the Importance of Excipient Testing in a Diagnostic Algorithm.

BACKGROUND: True corticosteroid (CS) allergy is rare. Instead, many patients may be allergic to excipients found in various CS preparations. Excipient testing is frequently overlooked. It might lead to unnecessary CS avoidance or dangerous re-exposure. OBJECTIVE: The objective of this study was to evaluate the clinical characteristics and frequency of excipient allergy in patients with confirmed type I hypersensitivity to systemic CS preparations. METHODS: Patients with a confirmed diagnosis of allergy (positive skin test or drug provocation test [DPT]) or tolerance (negative DPT to CS) over the past 10 years were studied. Patient characteristics, index CS, route of administration, clinical indications, symptoms of index reaction, and outcomes of CS/excipient allergy testing were analyzed. RESULTS: Sixty-four patients underwent CS allergy testing. True CS allergy was confirmed in 9 of 64 (14%) patients. The majority (5/9, 56%) with positive skin tests or DPT were actually allergic to the excipients (2 to carboxymethylcellulose and 3 to polyethylene glycol) rather than the CS. Respiratory manifestations were significantly associated with confirmed allergy (odds ratio = 6.79 [95% confidence interval = 1.36-34.03], P = .02). CONCLUSIONS: Patients with respiratory manifestations were significantly more likely to be truly allergic. CS allergies are rare and may be overdiagnosed without excipient testing. We suggest the use of Carmellose eye drops as a readily available source of carboxymethylcellulose for testing and propose a comprehensive diagnostic algorithm for suspected CS allergy.