The ID50EAL method was only used once to determine which extract fulfilled these potency requirements. Since the original skin tests were done, representative extracts for each new
in vitro reference lot are purchased by the FDA from one of the major extract manufacturers. In an evaluation period, all manufacturers test the new standard reference against the old to see if the results are consistent. When this reference is approved by the manufacturers, it is used as the standard to evaluate new lots of standardized extracts.