Bowie & Dick test: What is it and why is it important?
Discover the importance of the Bowie & Dick test for verifying the effectiveness of sterilizing porous loads in autoclaves. Understand its significance in quality control.
The significance of the Bowie & Dick test emerged in the 1950s. Numerous hospitals in Great Britain identified deficiencies in the sterilization of some porous materials, such as gowns, papers, and ceramic containers. J.H. Bowie and J. Dick were two prominent researchers who sought a solution to this problem, which they successfully developed in 1963. This solution is now known as the test that bears their names.
Due to its importance, the British Ministry of Health included it in their daily testing regimen for all autoclaves in healthcare environments.
Currently, the Bowie & Dick test is used in laboratories worldwide, and in Spain, its use is recommended under the UNE-EN-ISO 17665 standard, “Sterilization of healthcare products.” In fact, this standard is derived from EN-554, “Validation and routine control of steam sterilizers,” which was adopted in Spain as UNE-EN-554.
Its closest antecedents date back to 2009, when the EN-17665 standard (Sterilization of health care products — Moist heat — Part 1: Requirements for the development, validation, and routine control of a sterilization process for medical devices) came into effect, replacing the EN-554:1995 standard.
In addition to being a test that measures the proper performance of an autoclave, the results can be used as expert evidence in cases of critical failures and legal contexts. For this reason, it is advisable to keep any obtained results and archive them properly with their corresponding date.
What does the Bowie & Dick test evaluate?
It is quite simple: the test evaluates whether the sterilization of certain porous components has been performed correctly.
This helps determine if the machine can effectively sterilize some types of materials. In other words, it is a test whose results diagnose the correct functioning of the autoclave. The Bowie & Dick test indicates whether steam penetration into the test pack was rapid and uniform and, therefore, whether it is possible to sterilize permeable and/or porous items. The test consists of a thermosensitive strip or sheet of paper (sensitive to heat), which changes color, typically from white to black, during the sterilization process. This color change indicates exposure to heat and steam.
There are different shades (pink, blue, etc.), depending on the brand. This sheet is placed in the center of a so-called pack, composed of foam rubber and other fibrous layers. One of the main characteristics of the paper sheet is the distinct geometric pattern of visible marks.
For the color change in the thermosensitive paper to occur, there must be a simultaneous increase in temperature and humidity. The resulting pattern and distribution provide insight into the sterilization process’s effectiveness.
There is one important fact, and that is that the exposure period must be at least 3.5 minutes, and the temperature range should be between 132 and 134℃.
The kit can be used to measure:
- The effectiveness of steam penetration in porous components.
- The temperature and pressure of steam during the sterilization phase.
Procedure and operation of the test
The test kit should not be prepared independently. Prepared kits available from manufacturers should be used to ensure that the test is conducted according to quality standards and regulations. Additionally, using stable materials is crucial, as their composition will not influence the equipment or leave residues.
At the beginning of each working day, the Bowie & Dick test should be performed to determine the correct operation of the autoclave.
The steps to follow are:
- Ensure that the interior of the machine is empty.
- Place the test near the drain (only one kit should be used per cycle, without introducing any other elements).
- Initiate the corresponding program: complete sterilization at 134℃ and 2.1 atmospheres of pressure for 3 minutes and 30 seconds.
- Once completed, verify the results: check if the color change on the paper is continuous and uniform or if there is any noticeable variation.
The result is obtained when the cycle ends and the color is checked. It is then compared with the validation sheet (control chart) included in each box.
The reading provides results even for unsatisfactory tests. If the color changes uniformly but is not the expected shade, it indicates that the steam is not fully saturated, even though the penetration was homogeneous.
If the test reveals an uneven tone, a defect is present that needs to be corrected. There are three independent causes that can occur simultaneously:
- Poor quality of the produced steam.
- Existence of leaks.
- Vacuum pump failures.
A poor result (as mentioned above) should be addressed by performing a second test. If this second test also results in failure, it indicates that the autoclave is not functioning correctly. In this case, it should not be used until the fault or malfunction is resolved. Given that the reasons and causes are varied, it is essential to have qualified personnel available to resolve any inconsistencies or doubts.
When should the Bowie & Dick test be performed?
It is recommended to perform this type of test periodically. In addition to the routine use outlined in the laboratory protocol, this test should also be conducted in the following scenarios:
- After any repair or maintenance operation, to ensure that the autoclave is operating correctly.
- If the autoclave has been out of use for an extended period.
Variations of the Bowie & Dick test: DART test
There are currently some variations of the Bowie & Dick test, the most popular being the DART test, which stands for Daily Air Removal Test. The application criteria for this test are outlined in ISO 11140-5:2007, Sterilization of health care products, Chemical indicators, Part 5: Class 2 indicators for Bowie & Dick type air removal tests. Known as the American version, the specifications for the package include that it is made of cotton and is conducted with cycles at 132℃ for 4 minutes.
Our autoclaves that surpass the Bowie & Dick test
Vertical autoclaves with super-drying and fast cooling system
Vertical laboratory autoclaves with prevacuums and drying
