The case for patch test readings beyond day 2. Notes from the lost and found department.
Additional patch test readings taken after 2 days (48 hours) are valuable in distinguishing false-positive reactions, which may occur up to 22% of the time. Second readings taken on days 3 through 7 may detect an additional 34% positive reactivity. Those reactions, both lost (initially positive, later negative) and found (initially negative, later positive) by delayed readings, require clinical correlation for relevance as do the readings that persist at and beyond day 2 (positive at both readings).
Rietschel
R L
RL
Department of Dermatology, Ochsner Clinic, New Orleans, LA 70121.
Adams
R M
RM
Maibach
H I
HI
Storrs
F J
FJ
Rosenthal
L E
LE
D000485:Allergens / Q000008:administration & dosage; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D010328:Patch Tests / Q000379:methods*; D012882:Skin Tests / Q000379:methods*; D013997:Time Factors
D000485:Allergens