Effect of light on tuberculin purified protein derivative solutions

The effect of light on the biologic potency of tuberculin purified protein derivative solutions at the concentrations commonly used in tuberculin skin testing programs in human and veterinary medicin was studied. Guinea pigs sensitized with bacille Calmette-Guerin were used to evaluate the potency of these solutions after exposure to light. The biologic potencies of solutions dispensed in colorless glass vials and exposed to daylight, fluorescent light, and ultraviolet light (366 nm) decreased significantly when compared to those of control solutions kept in the dark; solutions exposed to light assumed a deep brown color, whereas control solutions remained unaltered. The percentage loss of biologic potency decreased, whereas the absolute loss of potency, i.e., the loss expressed in tuberculin units, increased with tuberculin purified protein derivative concentration. In addition, after exposure to ultravoilet and, to a lesser degree, fluorescent light, the rubber stoppers of the colorless glass vials became sticky and adhered tightly to the glass. By contrast, the biologic potency of identical solutions dispensed in amber glass vials did not decrease significantly during 1 year of exposure to fluorescent or ultraviolet light. The solutions remained unaltered, and the rubber stoppers from all of the amber vials, whether exposed or not exposed to light, were not adversely affected. It is recommended that for storage of tuberculin the use of colorless glass or other containers that transmit ultraviolet light be discontinued.