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Abbott TB MDx Test Evaluated Favorably in European Study

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This story has been updated to include comments from Abbott.

NEW YORK (GenomeWeb) – A high-throughput drug-resistant tuberculosis test from Abbott has recently been evaluated in a European study, showing strength in its ability to detect certain kinds of drug resistance and comparably high sensitivity with specimens that contain low levels of bacteria.

Conducted by Synlab, a European laboratory service provider, and published in The Journal of Clinical Microbiology the evaluation examined 715 clinical specimens and included both respiratory and extra-pulmonary samples.

Synlab provides human and veterinary medical lab testing in full-service laboratories, smaller specialized labs, and hospital labs in Europe, study author Sabine Hofmann-Thiel told GenomeWeb in an email.

With head offices in Augsburg, Germany, Synlab's Gauting, Germany-based lab specializes in mycobacteriology diagnostics, performing services that include smear microscopy, direct molecular TB tests via PCR, culture of TB bacteria and non-tuberculous mycobacteria (NTM), screening for genetic resistance markers, differentiation and susceptibility testing of TB and NTM, as well as genotyping services and indirect immunological testing for TB, Hofmann-Thiel said.

The lab is also a World Health Organization supranational reference laboratory for TB and it processes more than 40,000 diagnostic mycobacteriology samples per year. It is therefore interested in evaluating and testing new diagnostic tools, explained Hofmann-Thiel.

Abbott's RealTime MTB test, or RT MTB, is a real-time PCR assay to detect Mycobacterium tuberculosis. The firm also offers an add-on reflex assay to detect isoniazid and rifampicin resistance in positive samples, the RealTime MTB INH/RIF Resistance test, or RT MTB INH/RIF.

Tuberculosis is among the top 10 causes of death globally, and Abbott is working to help achieve the World Health Organization’s goal of ending the TB epidemic by 2030, Klara Abravaya, senior director of research and development for molecular diagnostics at Abbott, told GenomeWeb in an email. "There is a need for centralized, high throughput, highly sensitive MTB detection in addition to the detection of resistance to the two most widely used firstline drugs, rifampicin and isoniazid," Abravaya added.

Abbott introduced the Abbott RealTime MTB and INH/RIF assays as promising and sensitive tools to accurately detect TB and genetic resistance markers, Synlab's Hofmann-Thiel said.

"We wanted to evaluate the performances and usefulness of the assays in a high-throughput laboratory," she said, adding that the Abbott m2000 platform is a widely used system worldwide and this evaluation might therefore be of interest to others as well.

While the Cepheid GeneXpert MTB/RIF has been extensively adopted and provides advantages as an initial TB test in decentralized laboratories, Hofmann-Thiel noted, "Different molecular TB tests may be needed at different levels of the health system."

Indeed, last year Abbott told GenomeWeb that centralized testing for TB can provide the ability to identify both isoniazid- and rifampicin-resistant strains as well as potentially offer improved sensitivity. Centralized testing can also offer expert technicians and higher throughput — the Abbott test runs on the firm's automated m2000 instrument, processing 94 clinical specimens per batch.

"We see potential impact of the Abbott system in laboratory centers of regions with high prevalence of TB," Hofmann-Thiel said, adding that, because the Abbott platform offers a combination of TB and viral diagnostics, "It might be of benefit for high-capacity interdisciplinary diagnostic centers analyzing TB and HIV samples."

Hofmann-Thiel and her colleagues compared the Abbott tests to mycobacterial culture and to the FluoroType MTB assay from Hain Lifesciences, using that firm's GenoType MTBDRplus assay and phenotypic drug susceptibility testing to compare isoniazid and rifampicin resistance results. These are the assays Synlab currently uses routinely.

Overall, the Synlab team found Abbott's RT MTB had a positivity rate of about 92 percent compared to culture, with smear-positive and smear-negative samples having a positivity rate of 100 percent and 76 percent, respectively. Sensitivity was also high, reaching more than 99 percent for all samples from which Mycobacterium tuberculosis complex bacterium were cultured and 100 percent for culture-negative samples.

Similar results for respiratory samples have been reported in three recent evaluations of the Abbott test, but these did not examine extrapulmonary samples. Importantly, the Synlab study found the test performed about as well on the 15 percent of its overall cohort that were extrapulmonary. In the past, this type of sample has been more problematic with the GeneXpert test.

The Cepheid system also does not currently offer isoniazid-resistance testing, although that firm's XDR-TB cartridge in development is being designed to detect resistance to isoniazid as well as other TB drugs.

Compared to the Hain assay, the Synlab researchers found 97 percent concordance with the Abbott RT MTB to detect TB bacterium. When the 233 RT MTB positive samples were then subjected to RT MTB INH/RIF testing, the group found a concordance of more than 99 percent compared to the Hain GenoType MTBDRplus.

The researchers also assessed the Abbott assay as "very easy" to handle, with about two hours of hands-on time for 96 samples, and results in approximately 10 hours. The resistance testing with RT MTB INH/RIF required only an additional 15 minutes hands-on time for PCR set up, according to the study.

Hofmann-Thiel noted that multicenter studies in high-prevalence regions evaluating the Abbott assays in direct comparison to the Cepheid system are now needed.

Last year, Abbott was selected by the Global Fund as a panel supplier to offer one low access price for HIV scale-up testing and services to low- and middle-income countries, as previously reported. The firm also committed to extend the low price to other important infectious disease tests available on the m2000 system including the TB assay, and those for hepatitis B and C viruses, human papillomavirus, and chlamydia and gonorrhea.