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Clinical, Public Health Labs Evaluate Luminex GPP Test Reproducibility, Cost Effectiveness


NEW YORK (GenomeWeb) — Luminex's xTAG Gastrointestinal Pathogen Panel is highly reproducible across clinical and public health laboratories and offers improved turnaround time and a more efficient workflow than conventional culturing methods, according to a new study.

Investigators from the City of Milwaukee Health Department and Le Bonheur Children's Hospital in Memphis compared the results of analyzing 167 samples using the GPP at both sites to assess the assay's clinical performance. The results of their evaluation were published online this month in the Journal of Clinical Microbiology.

As reported in the paper, the authors established sensitivity of 98.7 percent between labs with high positive and negative agreement values. Assay performance compared against confirmatory methods such as culture yielded similar results. And after performing additional analysis, the investigators concluded that the GPP is more cost effective than culturing, despite higher upfront reagent costs.

"This paper shows the value of GPP, its effectiveness, and its potential for adoption by clinical and public health labs," Sanjib Bhattacharyya, deputy director of the City of Milwaukee Public Health Laboratory and corresponding author on the paper, told BioArray News this week.

According to Bhattacharyya, the JCM paper is the first to provide a cost and efficiency analysis of the GPP compared to conventional methods, and could lead to further adoption of the test by other labs.

"In an era of reduced resources and shrinking laboratory workforce with minimal technical expertise, we believe our paper [will] encourage laboratories to explore the adaptation of GPP as a reliable culture-independent approach," he said.

Austin, Texas-based Luminex says its xTAG GPP can detect hospital-acquired infections, targeting 15 total gastrointestinal pathogens in a single bead array-based assay. The US Food and Drug Administration last year cleared an in vitro diagnostic version of the assay that contains 11 targets, all of which must be confirmed using another approach. A company spokesperson said this week that the firm is looking into adding the four remaining targets to its IVD panel.

Luminex has since seen increased adoption of the assay, and CFO Harriss Currie said earlier this year that Luminex expects xTAG GPP will be a key growth driver in 2014.

The City of Milwaukee Public Health Laboratory was among the earliest adopters of xTAG GPP and has been using the test since December 2012, a month before the FDA cleared the assay for clinical use on Luminex's LX 200 instrument. Last year, Bhattacharyya and colleagues further evaluated the FDA-cleared assay andpublished a comparison of xTAG GPP and culturing methods, arguing that the test should be adopted in public health labs as well as the clinical labs, such as Le Bonheur's Molecular Diagnostics Laboratory, to which Luminex has most aggressively been marketing the test.

As the Milwaukee lab is focused on public health monitoring and Le Bonheur is a clinical lab, Bhattacharyya said it made sense to evaluate the performance of xTAG GPP between the two. He noted that clinical labs are focused on the diagnosis of diseases while public health labs are more involved in pathogen surveillance, and that clinical labs tend to be for profit while public health labs are nonprofit, differences that could affect each lab's experience with the test.

"It is important to compare results between a clinical and public health lab to observe any differences in assay performance between laboratories, GPP assay reproducibility, and to identify operational differences, if any, for GI pathogen identification compared to conventional methods for stool culture," Bhattacharyya said.

As part of their assessment, the two labs performed a side-by-side analysis of 167 stool samples collected from pediatric and adult patients with symptoms for gastroenteritis between February and June 2013. Along with comparably high sensitivity rates and positive and negative agreement values, the investigators also compared the cost per specimen, turnaround time, and hands-on staff time for gastrointestinal pathogen diagnosis using conventional methods versus xTAG GPP.

Specifically, they divided labor costs into multiple categories, including reagents, labor, and scalability without additional labor costs. They determined a potential decrease in overall cost, though they acknowledged high reagent costs associated with xTAG GPP. Still, when compared with savings from cheaper labor and greater scalability, the investigators concluded that the additional reagent costs were not significant.

Bhattacharyya noted that xTAG GPP reduces overall lab costs by reducing the need for multiple tests and consolidating those assays into one IVD with high sensitivity and improved turnaround time.

"These would probably be the most critical determining factors to improve workflow — increase efficiencies [and] show the cost benefits when compared [with] the cumulative costs per specimen using multiple different assays," he said.

Amani Patel, technical director at Le Bonheur Molecular Diagnostics Laboratory, added that xTAG GPP can "reduce overall healthcare cost" in terms of patient isolation, antibiotic use, and other factors compared to conventional approaches. "GPP being a highly multiplex molecular method, is more specific, sensitive, and [provides a] faster result," Patel told BioArray News.

It is this "culture-independent, multiplex nature" that Bhattacharyya said makes xTAG GPP a preferable assay to conventional culture-based and biochemical testing approaches that "too often rely on the right kind of media, specimen transport, growth characteristics, and phenotypic observations, which could [result in a] misleading final identification."

Still, while the benefits of xTAG GPP may be obvious to Bhattacharyya and Patel, widespread adoption of the test will require a "culture shift" within public health and clinical labs, Bhattacharyya said. He said that the Milwaukee lab has been approached by a number of labs that are interested in adopting xTAG GPP but need additional support to make the jump.

"One of the key components of bringing in this technology goes beyond just laboratory capabilities," said Bhattacharyya. "It requires education for our clinical partners ... to understand the value of multiplexing and interpretation of test results when co-infections are detected," he said. "It would be a culture shift to a positive direction to impact and improve current stool practice."


One issue raised in the JCM paper is the necessity to confirm IVD results using other techniques, creating additional costs that may dissuade smaller labs from adopting xTAG GPP and clinical labs that do not have access to such alternative approaches.

While Bhattacharyya acknowledged this potential challenge to broader adoption of the test, he said that the FDA's recommendation could be temporary, especially as more studies on xTAG GPP's reproducibility and concordance with conventional methods are published.

"In fact, some of the GPP users in clinical laboratories do use GPP as a standalone test and perform additional culture or molecular confirmation if requested by the clinicians," Bhattacharyya said. "In those cases, it may be considered off-label, but our site comparison study showed the robustness and reproducibility of this assay."

In the meantime, labs that wish to adopt xTAG GPP might be able to circumvent the associated costs of confirming their findings by partnering with other institutions and pooling resources.

"The sharing of resources, technical knowledge, and clinical specimens between public health, academic, clinical and reference laboratory networks can aid these efforts by defraying testing costs and increasing specimen diversity and accessibility," the authors wrote in the paper.