Unsatisfactory Results

What is an "unsatisfactory result"?

If your sterilizer fails to kill all of the bacterial spores on your test strip, you will receive an unsatisfactory result.

A secondary confirmation is performed on all failed spore tests, to ensure an accurate result. Our laboratory technicians perform a technique called a Gram Stain, to verify the presence of Geobacillus stearothermophilus or Bacillus atrophaeus in your sample.

Your office will receive a phone call and email informing you of your results.

What are my next steps?

Several factors may cause a biological indicator test failure, and a single failure is not necessarily an indicator of faulty equipment. It is important to retest your sterilizer as soon as possible.

CDC Recommendations

Steam Autoclaves

In the event of an unsatisfactory spore test on a steam autoclave:

  • The sterilizer should be removed from service, and all records reviewed of chemical and mechanical monitoring since the last negative BI test.
  • Sterilizer operating procedures should be reviewed, including packaging, loading, and spore testing, with all persons who work with the sterilizer to determine whether operator error could be responsible


If the repeat test is negative and chemical and mechanical monitoring indicate adequate processing, the sterilizer can be put back into service.

If the repeat BI test is positive, and packaging, loading, and operating procedures have been confirmed as performing correctly, the sterilizer should remain out of service until it has been inspected, repaired, and rechallenged with BI tests in three consecutive empty chamber sterilization cycles. When possible, items from suspect loads dating back to the last negative BI should be recalled, rewrapped, and resterilized.

Other Sterilizers

In the event of an unsatisfactory spore test on a non-steam autoclave (e.g., dry heat, unsaturated chemical vapor, ETO, or hydrogen peroxide gas plasma):

  • Any positive spore test is assumed to represent sterilizer malfunction and requires that all materials processed in that sterilizer, dating from the sterilization cycle having the last negative biologic indicator to the next cycle indicating satisfactory biologic indicator results, should be considered nonsterile and retrieved, if possible, and reprocessed or held in quarantine until the results of the repeat BI are known.


Below are the 3 most common causes of sterilization failure.


Improper Test Conditions

Check to ensure the sterilizer was set using the proper test conditions (Temperature, Time, Pressure). Most steam sterilizers operate between 250 – 270 degrees F. Temperatures outside of this range will likely fail to kill all organisms.


Exceeded Load Capacity

Verify that the sterilizer was not overloaded when the strip was run. It is important not to exceed the load capacity as it is listed. The steam/heat/vapor must be able to flow around each item being sterilized.


Faulty Door Gasket

Check the door gasket on the sterilizer. A cracked or improper fitting gasket will impair the ability of the sterilizer to reach the proper pressure. Loss of pressure can result in inadequate sterilization.

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PO Box 847

Ferndale, WA 98248

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