Comparing a New C difficile Test to the Standard Diagnostic Tool

Paul A. Granato, PhD

A novel Clostridium difficile diagnostic test is a reliable option for clinical laboratory use, according to a new study.

In general, nucleic acid amplification tests like polymerase chain reaction assays are the preferred test for diagnosing C difficile infection; however, recently, new tests have been cleared by the FDA. One of these tests, called the cobas Liat Cdiff nucleic acid test performed on the cobas Liat System can diagnose C difficile infection in 20 minutes. Specifically, it detects the C difficile tcbB gene which indicates the infection.

As senior study author Paul A. Granato, PhD, told MD Magazine^®: “C difficile gastrointestinal infection is a serious, potentially life-threatening disease. Its rapid and reliable laboratory diagnosis is important for proper patient therapeutic management and the early implementation of appropriate infection prevention measures for hospitalized patients and individuals living in extended care facilities.”

Investigators from upstate New York used 310 prospectively-collected stool samples that were tested for signs and symptoms of C difficile infection in order to evaluate the novel C difficile diagnostic tool in clinical settings.

The stool samples were tested using the standard test as well as the cobas Liat Cdiff tests at 2 sites (Syracuse, New York, and Minneapolis, Minn.) Initially, the investigators expected a minimum of 50 stool samples with positive results from the group of 300, which would definitively determine statistical agreement between the cobas Liat Cdiff and the standard test.

In total 55 stool samples tested positive for C difficile infection according to the standard test, the investigators reported. Then, the team calculated the overall percent agreement (OPA), positive percent agreement (PPA), and negative percent agreement (NPA) between the 2 tests, and found that the OPA, PPA, and NPA between the 2 tests were 96.4%, 94.5%, and 98%, respectively.

“Experience with the cobas Liat C difficile PCR test has shown that it compares favorably with a well-established, reference molecular method and that is a user-friendly assay that can be performed as an on-demand test by all laboratory shifts with reliable final test results available within 20 minutes,” Granato explained.

The study authors said this is the first study of its kind to compare the 2 diagnostic tools using symptomatic patient stool samples. In the past, other studies have compared tools, but they had lower concordance rates of 93% and 90%.

“The cobas Liat Cdiff test’s simplicity of use, rapid result reporting, and high sensitivity for C difficile tcdB gene detection offer an additional sensitive and reliable technological option for small- and medium-sized laboratories to perform this diagnostic service,” the study authors said.

They added that the 2 tests are “equivalent,” but further studies investigating how the tool can reduce the time to diagnosis, improve C difficile infection management, and contain the spread of infection within and outside the health care settings are still needed.

The study was funded by Roche, who developed the cobas Liat System.

The paper, titled “Performance comparison of the cobas Liat and Cepheid GeneXpert systems for Clostridium difficile detection,” was published in PLOS One.