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+1 (801) 290-7500
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D-Value Determination Studies

The D-value Determination test ascertains the resistance of a biological indicator (BI), product, or environmental isolate to sterilization by determining its resistance to a sterilant such as ethylene oxide, dry heat, or saturated steam under pressure. This test can also be used to determine approximate cycle times. Newly purchased BIs, inoculated actual product, pharmaceutical products, and isolates of microorganisms recovered during testing should be tested.

USP <55>, <71>, <1035>, & <1211> , ANSI/AAMI/ISO 11135, ANSI/AAMI/ISO 14161 and ANSI/AAMI/ISO 11138 each give guidance for the various methods used to calculate D-values. Equipment performance requirements are outlined in ANSI/AAMI/ISO 18472 for accurate determinations of the D-value.

Nelson Labs have steam and EO BIER vessels designed to meet these requirements. Our highly qualified personnel are knowledgeable in the Stumbo-Murphy-Cochran, Spearman Karber, Limited-Spearman-Karber, Holcomb-Spearman-Karber, and Limited Holcomb-Spearman-Karber methods.

Applicable Standards

  • ANSI/AAMI/ISO 11135
  • ANSI/AAMI/ISO 14161
  • ANSI/AAMI/ISO 11138
  • ANSI/AAMI/ISO 18472

Testing Locations

Study Outline

The D-value Determination test is mainly used to verify the labeled D-value of BIs to confirm their suitability for use and to determine the resistance of inoculated products, process challenge devices (PCDs), and isolates recovered from bioburden, environmental monitoring, or product sterility tests.

D-value, or decimal reduction time, is the time it takes to reduce a microbial population by 1 logarithm, or 90% of its initial value, under specified conditions (e.g., sterilant concentration, exposure temperature, relative humidity, package configuration).

In this test, samples are placed in a BI Evaluation Resistometer (BIER) vessel in such a manner to allow equal exposure on all sides. Multiple cycles are performed under the same parameters with the only variable being time. Following each exposure, the samples are tested for sterility or assayed for the number of surviving spores. The number of cycles, intervals between cycles, choice of sterility testing or population enumeration, and the calculations depend on the choice of D-value method.

When the test is performed to verify the manufacturer’s labeled D-value, it is important to apply the same method utilized by the BI manufacturer, due to inherent differences in BIER vessels, growth medium, change in resistance due to storage and shipping, and test methods. USP <1035> requires third-party verifications to be within 20% of the manufacturer’s labeled claim. ISO 11138 states that the 20% requirement only applies when performed by the same manufacturer due to inherent variability. So, it is important to understand with which standard you wish to comply.

Please include the BI manufacturer’s certificate of analysis when submitting samples.

If you have additional questions about D-value Determination tests, or would like to consult with the experts at Nelson Labs, just send us a request or call us at +1 (801) 290-7500.