Positivity ratio and reaction index: Patch-test quality-control metrics applied to the North American Contact Dermatitis Group database

Erin M. Warshaw, David D. Nelsen, Denis Sasseville, Donald V. Belsito, Howard I. Maibach, Kathryn A. Zug, Joseph F. Fowler, James S. Taylor, Vincent A. DeLeo, James G. Marks, Frances Storrs, C. G Toby Mathias, Melanie D. Pratt, Robert L. Rietschel

Research output: Contribution to journalArticle

31 Scopus citations

Abstract

Background: The positivity ratio (PR) and reaction index (RI) characterize the ability of patch-test preparations to produce strong (++ or +++) reactions as opposed to weak (+), questionable, or irritant reactions. Objective: This study evaluates these measures for North American Contact Dermatitis Group (NACDG) patch-test preparations. Methods: The PR and RI were calculated for 79 NACDG standard allergens tested from 1994 to 2006 (n = 26,479 patients). The median values were used as cutoff values for "acceptable" versus "problematic" preparations. Results: The top 10 "acceptable" patch-test preparations (PR ≤ 55 and RI > 0.46) were mixed dialkyl thioureas 1% in petrolatum (pet), tixocortol-21-pivalate 1% pet, ethylenediamine dihydrochloride 1% pet, sesquiterpene lactone mix 0.1% pet, nickel sulfate 2.5% pet, bacitracin 20% pet, thimerosal 0.1% pet, epoxy resin 1% pet, colophony 20% pet, and mercaptobenzothiazole 1% pet. The most "problematic" patch-test preparations (PR > 55 and RI ≤ 0.46) were cocamidopropyl betaine 1% aqueous (aq), benzalkonium chloride 0.1% aq, jasmine absolute 2% pet, iodopropynyl butyl carbamate 0.1% pet, 2-bromo-2-nitropropane-1,3-diol 0.5% pet, methyldibromoglutaronitrile 0.4% pet, methyldibromoglutaronitrile/ phenoxyethanol 2% pet and 2.5% pet, dimethylol dihydroxyethyleneurea 4.5% aq, and clobetasol-17-propionate 1% pet. Conclusion: Caution should be used when interpreting reactions to "problematic" patch-test preparations with a high proportion of weak, irritant, and questionable reactions.

Original languageEnglish (US)
Pages (from-to)91-97
Number of pages7
JournalDermatitis
Volume21
Issue number2
DOIs
Publication statusPublished - Apr 2010
Externally publishedYes

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ASJC Scopus subject areas

  • Dermatology
  • Immunology and Allergy

Cite this

Warshaw, E. M., Nelsen, D. D., Sasseville, D., Belsito, D. V., Maibach, H. I., Zug, K. A., ... Rietschel, R. L. (2010). Positivity ratio and reaction index: Patch-test quality-control metrics applied to the North American Contact Dermatitis Group database. Dermatitis, 21(2), 91-97. https://doi.org/10.2310/6620.2010.09092