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Sterilizer Testing: When to Use BI, Bowie-Dick, and Leak Tests

Three core tests form the foundation of steam sterilizer verification: biological indicators (BI), Bowie-Dick tests, and leak (vacuum) tests. Each serves a distinct purpose.

 

Biological Indicator (BI) Testing: Was sterilization achieved?

Biological indicators provide the most direct confirmation of sterilization by verifying that microorganisms have been destroyed.

 

As recommended by ANSI/AAMI ST79, a reference for best practices and guidelines used here in the United States, BI testing should be performed;

  • At least weekly (minimum) and preferably daily when the sterilizer is in use
  • After installation or relocation
  • Following major repairs or process failures
  • After changes/repairs to utilities (steam, water, boiler, etc.)

 

During qualification testing, three consecutive BI tests must pass.

Sterile processing departments can also reference the standard to define what qualifies as major repairs and changes, like installation and during maintenance work.

 

Bowie-Dick Testing: Is air being removed properly?

Bowie-Dick testing applies to all pre-vacuum sterilizers and verifies effective air removal and steam penetration. Bowie-Dick testing confirms the proper removal of air and adequate steam penetration.

 

ANSI/AAMI ST79 recommends:

  • Daily, before the first load
  • At a consistent time, each day
  • After installation, relocation, or major repairs
  • After process failures

 

During qualification testing, three consecutive Bowie-Dick tests must pass.

Leak (Vacuum) Testing: Is the chamber holding vacuum?

Leak testing evaluates whether the sterilizer can maintain a proper vacuum which is critical for air removal. Leak testing helps identify issues before they show up as Bowie-Dick or BI failures.

Leak testing should be performed as recommended by the device manufacturer. Many manufacturers including SteelcoBelimed require weekly leak testing.

 

When Is Qualification Testing Required?

Qualification testing is required whenever sterilizer performance may be impacted. According to ANSI/AAMI ST79 this includes:

  • Installation or relocation
  • Sterilization process failures
  • Changes/repairs to utilities (steam, water, electrical supply)
  • Major repairs


A major repair is any work beyond routine maintenance, such as:

  • Replacement of a vacuum pump or chamber door
  • Control system upgrades
  • Major piping or utility changes
  • Repairs to the pressure vessel

 

Routine preventive maintenance items (gaskets, valves, etc.) does not require full requalification.

 

During qualification:

  • Three consecutive BI tests must pass
  • Three consecutive Bowie-Dick tests must pass (pre-vacuum sterilizers)

 

This testing is completed before the sterilizer is returned to service.

 

Final Thoughts:

 

Each test answers a different question:

  • BI testing: Was sterilization achieved?
  • Bowie-Dick testing: Is air being removed properly?
  • Leak testing: Is the chamber holding vacuum?

 

When applied together and aligned with ANSI/AAMI ST79, these tests provide a complete and reliable picture of sterilizer performance.

 

Reference: ANSI/AAMI ST79:2017 & 2020 Amendments A1, A2, A3, A4 (Consolidated Text) Comprehensive guide to steam sterilization and sterility assurance in health care facilities