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AST News Update June 2022: Updating Breakpoints–New Developments from CAP


Romney M. Humphries, Vanderbilt University Medical Center, Nashville, TN

The College of American Pathologists (CAP) is introducing two new requirements for clinical laboratories to use updated breakpoints (BPs) when interpreting antimicrobial susceptibility testing (AST) results. CAP has recognized that some laboratories are using obsolete breakpoints,1,2 even when devices have achieved US Food and Drug Administration (FDA) clearance for updates, which could lead to adverse consequences in managing patients.

In brief, laboratories will be required to:

Step 1
Determine and document which BPs are used in their laboratory for minimal inhibitory concentration (MIC) and/or disk diffusion tests. This involves checking all places where BPs are applied including the AST instrument, laboratory information system (LIS) and
electronic health records (EHR). This new requirement is effective now.

Step 2
Identify obsolete BPs in use and make a plan to update BPs to current BPs that were updated prior to 2021. Labs will have 3 years to update BPs following FDA publication of BPs update. This new requirement will be effective January 2024.

The CAP Checklist Items Describing the New Breakpoint Requirements3

“Revised MIC.11380 9/22/2021 Antimicrobial Susceptibility Test Interpretation Criteria
(Previously MIC.21930 (Susceptibility Test Endpoint Determination) For antimicrobial susceptibility testing systems, there are written criteria for determining and interpreting minimal inhibitory concentration (MIC) or zone diameter sizes as susceptible, intermediate, resistant, non-susceptible, or susceptible dose-dependent. These criteria are reviewed annually.”

What this means:

  • Laboratories must know what BPs are in use in their laboratory.
  • Laboratories must review and document the BPs applied in their laboratory annually.
  • Laboratories should discuss breakpoints in use with their antimicrobial stewardship team, as appropriate.

“New MIC.11385 9/22/2021 Current Antimicrobial Susceptibility Test Interpretation Breakpoints
Effective January 1, 2024, the laboratory uses current breakpoints for interpretation of antimicrobial minimum inhibitory concentration (MIC) and disk diffusion test results, and implements new breakpoints within three years of the date of official publication by the FDA or other standards development organization (SDO) used by the laboratory.”

What this means:

  • Effective January 1, 2024 laboratories must use current BPs for MIC and disk diffusion tests.
  • At minimum, US laboratories must use current FDA BPs, but laboratories may choose to use current CLSI or EUCAST BPs.
  • It will be UNACCEPTABLE for laboratories to use BPs that are no longer recognized by either FDA, CLSI, or EUCAST.
  • In rare cases, a laboratory can use alternative BPs (including old breakpoints), if justified. This would require documentation that would optimally include input from the institution’s antimicrobial stewardship team.

To learn more, an archived version of the January 2022 CAP-CLSI webinar can be accessed and purchased here.

Additional Resources to Get Started!

CLSI ORWG has developed an optional spreadsheet that laboratories can use to record breakpoints in use; this can be found here.

Please note that CAP is not prescriptive on the method used to document BPs in use. The Association of Public Health Laboratories provides a Breakpoint Implementation Toolkit for updating carbapenem breakpoints which can be found here.

CLSI and other organizations are in the process of preparing additional tools to help laboratories with the task of updating breakpoints on their AST systems.


1. Simner PJ, Rauch CA, Martin IW, et al. Raising the bar: Improving antimicrobial resistance detection by clinical laboratories by ensuring use of current breakpoints. Open Forum Infect Dis. 2022;9 (3). doi.org/10.1093/ofid/ofac007.
2. Newitt, VN. AST and safety at core of microbiology checklist changes. CAP Today. October 2021.
https://www.captodayonline.com/ast-and-safety-at-core-of-microbiology-checklist-changes/. Accessed May 17, 2022.
3. College of American Pathologists, Council on Accreditation. All Common Checklist. September 22, 2021 ed. Northfield, IL: College of American Pathologists; 2021.


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