Positivity ratio and reaction index: patch-test quality-control metrics applied to the north american contact dermatitis group database.
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 < or = 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 < or = 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.


CONCLUSIONS
Caution should be used when interpreting reactions to "problematic" patch-test preparations with a high proportion of weak, irritant, and questionable reactions.
Warshaw
Erin M
EM
Department of Dermatology, Department of Veterans Affairs Medical Center, Minneapolis, MN, USA.
Nelsen
David D
DD
Sasseville
Denis
D
Belsito
Donald V
DV
Maibach
Howard I
HI
Zug
Kathryn A
KA
Fowler
Joseph F
JF
Taylor
James S
JS
DeLeo
Vincent A
VA
Marks
James G
JG
Storrs
Frances J
FJ
Mathias
C G Toby
CG
Pratt
Melanie D
MD
Rietschel
Robert L
RL
D000485:Allergens; D001414:Bacitracin; D052160:Benzothiazoles; D003877:Dermatitis, Contact / Q000175:diagnosis*; D004853:Epoxy Resins; D005029:Ethylenediamines; D006801:Humans; D006854:Hydrocortisone / Q000031:analogs & derivatives; D007783:Lactones; D009532:Nickel; D010328:Patch Tests; D011786:Quality Control; D012717:Sesquiterpenes; D013849:Thimerosal; D013890:Thiourea / Q000031:analogs & derivatives
D000485:Allergens; D052160:Benzothiazoles; D004853:Epoxy Resins; D005029:Ethylenediamines; D007783:Lactones; D012717:Sesquiterpenes; D001414:Bacitracin; D013849:Thimerosal; C029938:nickel sulfate; C031234:ethylenediamine; C019112:tixocortol pivalate; D009532:Nickel; D013890:Thiourea; D006854:Hydrocortisone