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Sterility Testing for Medical Device

Updated: Nov 2, 2023

What is Sterile?

According to ISO11737-1, an item or product is considered sterile when it is free from viable microorganisms. Viable here means that the microorganisms are alive and able to reproduce. Viable microorganisms are a concern for sterile medical devices because only viable microorganisms can reproduce on the surface of a product, inside a product, and in the human body causing sickness and disease.

What is Sterility Testing?

The term “Sterility Test” generally refers to a test that investigates the presence or absence of microorganisms or microbial growth. There are two definitions for sterility testing as described in ISO document 11737-2 (2019). The first one is the “Test of Sterility” which refers to sterility tests done during the development, validation, or requalification of a sterilization process. The second one is “Test for Sterility” which ISO 11737-2 and USP <71> describe as a technical operation specified in a pharmacopoeia performed on a product following an aseptic process or exposure to a sterilization process. USP <71> further states that tests for sterility “are not by themselves designed to ensure that a batch of product is sterile or has been sterilized. This is accomplished primarily by validation of the sterilization process or of the aseptic processing procedures. A satisfactory result only indicates that no contaminating microorganism has been found in the sample examined in the conditions of the test.”

What is SAL?

A product or device that is labelled as sterile must undergo a validated sterilization process to make it sterile or to achieve the required sterility assurance level (SAL). SAL is defined as the “probability of a single viable organism occurring on an item after sterilization. The SAL of a product can be 10-6 or 10-3, depending on the intended use of the product. A SAL of 10-6, for example, defines the probability of 1 in 1 000 000 that a device is not sterile. SAL is a probability that can never be reduced to zero because the rate of inactivation of microorganisms by a sterilant is exponential.

Sterility Test Methods

1. Direct Inoculation of products The whole product or a sample item portion (SIP) is aseptically immersed into a culture medium and incubated for 14 days. The choice of culture medium and incubation conditions depends on the nature of the product, the method of manufacture, the sources of potential microbial contamination, and the types of microorganisms likely to be encountered.

2. Removal of microorganisms by elution The product is washed/rinsed with a suitable culture medium or eluent solution to remove any microorganisms on the product. If culture medium is used as the eluent, after washing/rinsing, the medium is incubated for 14 days. If eluent solution is used, after washing/rinsing the product, the solution can be filtered through a membrane filter or added to equal volume of double-strength culture medium and then incubated for 14 days.

3. Membrane filtration of liquid products Liquid products are filtered through a membrane filter aseptically and the membrane filter is immersed in a suitable culture medium and incubated for 14 days.

Method Suitability Test: Bacteriostasis and Fungistasis Test (B/F)

The Bacteriostasis and Fungistasis Test (B/F) is also known as the Sterility Method Suitability Test. The test is performed on a sterile product for the purpose of finding if any inhibitory substances are being released by the product which would invalidate a sterility test. Products that release inhibitory substances will falsely show a satisfactory result during sterility testing. The test method will therefore confirm the presence or absence of inhibitory substances in the medical devices that could affect the result of sterility test. The test is usually required during the course of validation or maintenance of a sterilization cycle; and is done on any product that needs any form of sterility testing.

Sterility Test for Medical Devices at SaniChem Resources

SaniChem offers a few variations of sterility test methods to suit customers' validation requirements. Our accredited methods are:

  1. TM-500 Sterility Test of Medical Devices: Direct Immersion Method (based on ISO 11737-2:2019)

  2. TP-503 Sterility Test of Medical Devices: Direct Inoculation (based on USP <71>)

  3. TM-501 Sterility Test of Biological Indicator: Direct Immersion Method (based on ISO 11138-1:2017)

  4. TM-504 Bacteriostasis and Fungistasis Test for Medical Device (based on ISO 11737-2:2019 and USP <71>)

SaniChem Resources is happy to accommodate your needs if you require other kinds of sterility testing. Do drop us an email at or contact us at +606 794 7606.

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