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AST and safety at core of microbiology checklist changes

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Valerie Neff Newitt

October 2021—By Jan. 1, 2024, laboratories must use current breakpoints to interpret antimicrobial minimum inhibitory concentration and disk diffusion test results, according to a new requirement in the latest edition of the CAP Accreditation Programs microbiology checklist, released Sept. 22.

The same requirement calls for laboratories to implement new breakpoints within three years of the official publication date of the updated breakpoint.

“That is going to be a challenge and real work for a lot of laboratories,” Sheldon Campbell, MD, PhD, a member of the CAP Checklists Committee, says of the new requirement (MIC.11385 Current Antimicrobial Susceptibility Test Interpretation Breakpoints). His advice to laboratories: “Start thinking now about how you are going to accomplish that.”

Dr. Campbell

The new requirement is one of several changes to the 2021 microbiology checklist. Those changes were made for three main reasons, the first having to do with clarity.

“We looked at things labs are struggling with and tried to make the requirements clearer and more accessible to users,” says Dr. Campbell, professor of laboratory medicine at Yale School of Medicine and director of laboratories at the VA Connecticut Healthcare System.

The safety of clinical laboratory personnel is the second reason. In prior versions of the microbiology checklist, the safety requirements were in each of the subdiscipline sections. Those requirements have been updated and moved to a dedicated section on safety. “We removed redundant items from each microbiology section and instead combined them where appropriate,” says Christina Wojewoda, MD, chair of the CAP Microbiology Committee and associate professor and director of microbiology, University of Vermont Medical Center.

The third reason is to improve patient care, particularly around antimicrobial susceptibility testing.

“There’s a fair amount of misunderstanding in the laboratory community about susceptibility testing—how to interpret the laboratory results and provide real meaning for clinicians,” says Carol A. Rauch, MD, PhD, a member of the CAP Microbiology Committee and CDC Antibiotic Resistance Laboratory Network technical laboratory liaison.

Dr. Rauch

“There’s a constant background of organisms evolving to develop new resistance,” she continues. “The community as a whole has to keep up with new guidelines, new test methods, new ways of interpreting those results. The interpretations are focused on criteria we call breakpoints, which identify resistance or not, and where we make those cutoffs has been a moving target—with a lot of movement—over recent years. We need to get everybody onto the same page.”

Dr. Wojewoda says a checklist requirement on the use of updated breakpoints to interpret susceptibility testing is something the members of the Microbiology Committee have thought about as a committee for several years. “We finally got it across the finish line this year,” she says. “A lot of deliberation went into that, especially the phased rollout plan where we are giving labs a date to aim toward. We know this could be a burden for some laboratories, but it’s the best for patient safety and care.”

Dr. Wojewoda notes the three years of “wiggle room” laboratories will have to reach compliance: “We are giving labs until January 2024 to get their assays validated to use the most current breakpoints.” After that, she says, new validations will be needed indefinitely as new breakpoints continue to emerge.

Says Dr. Rauch: “This will sound daunting to labs that didn’t even know there was a problem with breakpoints. However, the Microbiology Committee does plan to provide support in the form of webinars, podcasts, documents, slide sets, et cetera. We’ve been gathering those materials so that laboratories are not left on their own.”

Dr. Campbell says some manufacturers of automated systems can be slow to update their breakpoints, so this puts more work on the laboratory to get those breakpoints updated. “Hopefully, this will put a little pressure on manufacturers to move faster.”

A related and revised requirement in the checklist edition released last month is MIC.11380 Antimicrobial Susceptibility Test Interpretation Criteria. It says there must be written criteria for determining and interpreting minimal inhibitory concentration or zone diameter sizes as susceptible, intermediate, resistant, nonsusceptible, or susceptible dose-dependent, and the criteria must be reviewed annually.

“To improve performance of susceptibility testing and provide actionable reports to our clinicians,” Dr. Rauch says, “this requirement focuses on the lab knowing what breakpoints it is using. It sounds obvious, but it’s actually a tricky question that may involve contacting the manufacturer of a commercial device.” This dialog may be an “eye-opening experience” for many labs, she says, because they may assume the manufacturer of an FDA-cleared device is using updated breakpoints. “But that is not necessarily true. For example, breakpoints sometimes have lowered, and an organism with a certain minimum inhibitory concentration, once considered susceptible, now may be called intermediate or resistant. That has direct patient clinical care consequences, as well as possible public health consequences. We must make sure laboratories are using up-to-date information to classify the bacteria.”

The revised requirement says a laboratory must select criteria, apply them appropriately, and reference them in its procedures, Dr. Campbell says. “In addition, the laboratory must talk to a manufacturer to find out what breakpoints are applied, then review criteria annually, because that is the time frame in which resistance changes.”

In the bacteriology section of the checklist is a new requirement on susceptibility testing. MIC.21855 Antimicrobial Resistance Markers by Molecular Analysis—Clinical Validity requires the detection of genotypic antimicrobial resistance markers—for example, vanA, mecA, blaKPC—to be linked or attributed to a corresponding organism in the final laboratory report when molecular analysis is performed directly on patient specimens, such as urine or bronchoalveolar lavage fluid. This can be accomplished through molecular detection of the corresponding organism or concurrent culture.

The problem, Dr. Campbell says, is “when you detect a gene for an antimicrobial resistance marker, all you detect is the gene. You don’t know the context of it or what organism it is in. This checklist item requires specific tests so that when antimicrobial decisions are going to be made, that gene will be linked to an organism.”

Linking the resistance mechanism to the organism will make it possible for clinicians to understand how best to treat patients, Dr. Wojewoda says. “We’re asking the labs to culture the specimen so they can do susceptibility testing on that organism to ensure the resistance mechanism is associated with that organism. However, it’s important for labs to understand that the requirement does not include screening tests. It is for specimen-based testing for patient care only.”

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