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False-Positive Intradermal Skin Tests and Thimerosal

Howard I. Maibach, MD
JAMA. 1972;220(1):126. doi:10.1001/jama.1972.03200010110027.
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To the Editor.—  In 1963, Epstein (J Allerg34:225) showed delayed hypersensitivity to thimerosal (Merthiolate) as a cause of false-positive delayed skin tests. Recently Hansson and Möller demonstrated peculiar patch test reactions to thimerosal in healthy young adults (Brit J Derm83:349, 1970). This led them to intradermal skin test 412 young healthy Swedish recruits with old tuberculin (OT) which in Sweden contains thimerosal as a preservative purified protein derivative (PPD) (not containing thimerosal) and thimerosal in saline (Scand J Infect Dis3:169, 1971).A positive reaction to thimerosal was recorded in 15% of the men. They found that thimerosal influenced the reactions in 63 of the 163 positive OT tests. On this basis they recommend that thimerosal not be added to intracutaneous test solutions (for delayed hypersensitivity) since the thimerosal may interfere with the evaluation of positive reactions.In the United States most commercial sources of


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