A retest cannot, by itself, invalidate a “Not Sterile” result. USP <71> states that in addition to a passing retest, one of the following conditions must be met in order to invalidate the original result:
- The data of the microbiological monitoring of the sterility testing facility show a fault.
- A review of the testing procedure used during the test in question reveals a fault.
- Microbial growth is found in the negative controls.
- After determination of the identity of the microorganisms isolated from the test, the growth of this species (or these species) may be ascribed unequivocally to faults with respect to the material and or the technique used in conducting the sterility test procedure.
This depends on the contaminant identified. This is very important however, as understanding the natural habitat of a sample contaminant can assist in identifying how the contaminant made its way into the sample product. This information can guide effective response steps.
Thorough investigation of any contamination event is an important part of good quality system. Without proper identification of the contaminant, it is difficult to determine how the product became contaminated, and thus what corrective action steps may be appropriate.
Retesting of the product is one part of the endotoxin out-of-specification investigation process. A retest may either confirm or call into question the initial result. A single passing retest is not sufficient to invalidate the original result. However, it does provide evidence that a test fault may have occurred.
There are certain times when a sample article is not large enough to perform sufficient out-of-specification investigation testing. In these instances, it may be impossible to determine the actual cause for the elevated test result.
Though we do everything we can to limit testing errors, it is possible to have an internal contamination event while performing sample preparation or testing. This most commonly occurs through inadvertent splashing of control standard endotoxin solutions, which are used for standard curve and positive control preparation on every test plate. Thorough precaution is taken to ensure internal contamination events are minimal and impact to client’s test results are rare.