New report helps veterinarians interpret susceptibility test data

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Confused by breakpoints, susceptibility test results, and lab techs who speak gobbledygook?

Help is here.

The Clinical and Laboratory Standards Institute (CLSI) has just come out with a new report to help veterinarians better understand antimicrobial culture and susceptibility test results.

The report, VET09—Understanding Susceptibility Test Data as a Component of Antimicrobial Stewardship in Veterinary Settings (VET09), will also help bridge the communication gap between veterinarians who submit those tests and the lab technicians who process them—two groups who don’t always speak the same technical language.

CLSI is a not-for-profit membership organization that creates best practices for clinical labs.

The report discusses antimicrobial susceptibility testing (AST) and provides veterinarians with background information about laboratory processes, including how AST is performed, reasons a veterinarian might not want to perform it, and how AST results are assessed by a laboratory.

It also provides examples of culture and susceptibility reports, plus species-specific guidance on applying breakpoints to interpret susceptibility test results of animals.

A breakpoint is a chosen concentration of an antibiotic that defines whether a species of bacteria is susceptible or resistant to the antibiotic. Breakpoints are determined by CLSI experts, and figuring out how to apply them is one of the most confusing aspects of AST testing.

“It’s a very complex issue,” Lori Moon, MS, MT (ASCP), senior project manager at CLSI, told NEWStat. CLSI publishes the breakpoints they come up with as well as the standards on how to do the testing. “But the veterinarians who are using the results of the testing don’t understand how the breakpoints are set, so they go to the lab for information on how that’s done.” But the people in the lab aren’t the ones who developed the breakpoints, so they’re missing the pharmacological and microbiological data needed to answer the veterinarians’ questions.

Hence the new report.

Moon said, “It’s a condensed version of the intersection of pharmacology and microbiological principles. So there’s some basic information about factors that affect drug absorption. A lab wouldn’t necessarily know that, but it’s something a veterinarian would want to know.” The report also includes other valuable information, such as how to take the best sample, and factors affecting the quality of the samples. “It’s an easy read,” she added (somewhat reassuringly).

Virginia Fajt, DVM, PhD, DACVCP, a clinical associate professor of veterinary physiology and pharmacology at Texas A&M University and chair of the CLSI subcommittee that wrote the report, told NEWStat that the CLSI decided to issue VET09 in order to clear up confusion.

“It’s become clear over the past few years . . . that there’s a lot of either misunderstanding of, or misuse of, results that come from antimicrobial susceptibility testing,” Fajt said. “So [the subcommittee] convinced CLSI to put all that information together [to create] one source of information for veterinarians who are using susceptibility data or trying to decide whether they should perform susceptibility testing. [The report teaches them] the best way to use that data, how to get the best data out of their results, and then how to interpret that data appropriately to make decisions about antimicrobial treatment.”

Fajt says that a lot of veterinarians use susceptibility data to help them make decisions, but they may not be using it as well as they could. Some may be misinterpreting the data. And some may not do susceptibility testing at all because they don’t fully understand how it works or how helpful it can be.

“So, part of the usefulness of the report is you might start to recognize that you could actually get more value out of that kind of testing than you thought you could,” Fajt said.

Find out more about VET09—Understanding Susceptibility Test Data as a Component of Antimicrobial Stewardship in Veterinary Settings here.

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