At intervals during the incubation period and at its conclusion, the media are examined for macroscopic evidence of microbial growth. If the material being tested renders the medium turbid so that the presence or absence of microbial growth cannot be easily determined by visual examination, 14 days after the beginning of incubation, portions (each not less than 1 ml) of the medium are transferred to fresh vessels of the same medium; then, the original and transfer vessels are incubated for not less than 4 days. If no evidence of microbial growth is found, the preparation under examination complies with the test for sterility. If evidence of microbial growth is found, the preparation under examination does not comply with the test for sterility. Do not repeat the test unless it can be clearly shown that the test was invalid for causes unrelated to the preparation under examination. The test may be considered invalid only when one or more of the following conditions are fulfilled:

1. Microbial growth is found in the negative controls.
2. Data on microbial monitoring of the sterility testing facility show a fault.
3. A review of the testing procedure used for the test in question reveals a fault.
4. After identifying the microorganisms isolated from the containers showing microbial growth, the growth may be ascribed without any doubt to faults with respect to the materials and/or technique used in conducting the test procedure.

If the test is declared to be invalid, it is repeated with the same number of units as in the original test. If no evidence of microbial growth is found in the repeat test, the preparation under examination complies with the test for sterility. If microbial growth is found in the repeat test and confirmed microscopically, the preparation under examination does not comply with the test for sterility.