The histamine content of allergen extracts

The histamine content of 108 inhalant, food, and venom extracts from four commercial sources was measured by chemical (glass fiber-based) and immunologic (competitive RIA) methods. Histamine was present in 64 of 76 inhalant extracts (range, 0.005 to 7.4 micrograms/ml), 20 of 26 food extracts (range, 0.16 to 23 micrograms/ml), and six of six venoms, 100 micrograms/ml (range, 1.0 to 38 micrograms/ml). Histamine was removed by treatment with diamine oxidase or dialysis of an extract. Repeat assay of selected extracts after addition of known amounts of histamine in the glass fiber-based method produced additive results, and glycerin- or phenol-extract preservatives did not affect assay performance. Timed extractions of dried-pollen grains demonstrated maximal histamine content at 30 seconds, suggesting that histamine is an inherent component of at least some pollens. Histamine found in some allergen extracts could, under extreme circumstances, produce false-positive results in skin testing and in basophil histamine release assays, and could affect the result of research that uses intact pollen or allergen extracts.