The need to redefine the unit of the international standard for tuberculin purified protein derivative (PPD-S).
It is well known that the results of the relative potency tests between tuberculin preparations and the standard can be affected by many variables. The authors emphasize that the single most important variable to control, to ensure that the potency tests are reproducible, is to prevent the depletion by adsorption of the tuberculin from the preparation. Evidence is presented to show the importance that adsorption, to glass and plastic surfaces, could have on the loss of tuberculin PPD during the preparation of dilute tuberculin solutions. It is suggested that a) an anti-adsorption agent be added to all diluents used to prepare tuberculin solutions, and b) the assignment of a new value to the International Unit for tuberculin PPD be considered.
D000327:Adsorption; D004355:Drug Stability; D005898:Glass; D012015:Reference Standards; D013997:Time Factors; D014373:Tuberculin / Q000592:standards*; D014944:World Health Organization
D014373:Tuberculin