Sterility testing

Sterility testing checks whether a sample contains any living microorganisms, either by incubating it in growth media as USP <71> describes or by a validated rapid method such as PCR.

The compendial method, USP <71>, either filters the sample through a membrane that is then placed in culture media, or adds the sample to the media directly. The media are incubated for at least 14 days and inspected for growth. Growth that cannot be traced to an error in the laboratory means the sample fails.

Rapid methods answer sooner. PCR-based tests detect microbial DNA, often a gene that all bacteria share, within hours rather than weeks. They measure something different from growth: DNA can remain from organisms that are already dead, and a test finds only what its primers are designed to detect. USP <1223> describes how a laboratory shows that a rapid method performs at least as well as the compendial one.

A sterility test examines only the units sampled, so it supports confidence in a lot rather than proving every vial sterile. That assurance comes from how the lot was made and filled. Sterility also says nothing about endotoxin, which dead bacteria leave behind, or about chemical purity, so a sterility entry on a certificate should be read alongside its endotoxin and HPLC entries.

Related terms

• Endotoxin
• Microbial limits testing
• Certificate of analysis

UPDATED OCTOBER 30, 2026 · REVIEWED BY DEL POTTER, PHD