HBsAg tests, mutation in public health spotlight

Create PDF

Dr. Patibandla

Says Dr. Patibandla of Siemens Healthineers: “When dealing with virology/serology assays, development at Siemens Healthineers is always ongoing to push for better sensitivity and specificity, to detect the virus earlier and more accurately to improve patient care. Siemens Healthineers developed our HBsII [hepatitis B surface antigen two] assay to enhance the assay’s sensitivity and ability to detect multiple viral mutations. Our R and D scientists developed a cocktail of antibodies to be used in the assay to achieve this.” The FDA approved the assay in 2014, she says.

Mutations in the “a” determinant region are particularly problematic, Dr. Patibandla says, because this highly immunogenic region is the primary target for surface antigen detection by immunoassays. To date, she says, several mutations associated with 28 different residues within the “a” determinant have been identified that affect HBsAg detection by immunoassays from various manufacturers. “Siemens has accumulated a number of mutants with the help of our surveillance program and based on those reported in the literature. We have reconfigured our HBsAg assay to be able to detect all these mutations. Thus, an important aspect of the Advia Centaur HBsII assay is the ability to detect HBsAg mutants, especially those arising in the ‘a’ determinant.”

Dr. Cloherty

Abbott Diagnostics has focused on making its assays as sensitive and as robust as possible, says Gavin Cloherty, PhD, director of the company’s infectious disease research for diagnostics. He points out that current Abbott Architect assays have a test sensitivity of .02 IU/mL, making them some of the most sensitive tests on the market.

“Our tests are used to screen more than half of the world’s blood supply, so we have to be on top of their sensitivity in the clinical context. Our global surveillance program has been in place for more than 20 years and scours the world looking for weird and wonderful viruses. And we continually look at how viruses are evolving and the impact that might have on our tests. We use this data to make sure that tests we build in the future are robust, which may involve adding new targets, antibodies, monoclonals, or whatever biological component is needed.”

The global surveillance is used for Abbott’s HBV tests. That includes, in addition to the HBsAg test, its RealTime HBV Viral Load Assay, a PCR test that runs on the Abbott m2000, Dr. Cloherty says. “Viruses don’t stay still. We have to stay one step ahead or they are going to get ahead of us.”

False-negatives due to mutant viral strains are not common but have occurred in the past, he adds. “We can use HIV as an example. It’s a very challenging virus, and there have been multiple zoonotic infections introducing very different strains of HIV into the human population. Back in the 1990s, when HIV group O variants were first identified, manufacturers had to reevaluate and add in components to allow their tests to robustly detect these new strains. And there have been other primate SIV introductions into the human population, known as group N and group P, which are also very different genetically from the more common group M.”

Abbott’s global surveillance program was able to identify more than half of the group N HIV viruses that have been reported in the world and one of the two known group P mutations, Dr. Cloherty says. “So we are keeping our finger on the pulse of HIV and viral hepatitis.” But a key thing to keep in mind from a diagnostic perspective, he says, is that the virus is so different throughout the world. “Different genotypes and different strains are constantly evolving or being introduced into the human population, in places that are just a plane ride away from the U.S.”

Hendrickson stresses that the Siemens HBsII detects the mutant strain sG145R and that some of the responsibility in this case was on the laboratory for not having up-to-date products. That laboratory (“Laboratory A” in the MMWR report) has subsequently changed its assay to HBsII. “The change had been in the pipeline, but maybe because of costs or prioritization, it wasn’t made as quickly as it could have been. They expedited it as a result of this case and our communications with them, so it has since been changed.”

As the coauthors emphasize in the MMWR report, this false-negative case demonstrates the importance of laboratories’ use of FDA-approved assays that have the ability to detect HBsAg mutants. But there is another important lesson from the case: “We can’t just be complacent and think, ‘We’ve got a good test,’ or ‘We have a good vaccine or good therapy for a very specific type of virus,’” Hendrickson says. “We need to understand the complexities of the viruses and how they’re changing so we can change our testing and interventions as needed. It’s such a long process to get biologics or testing instruments approved by the FDA, and appropriately so, that it’s a never-ending battle until the pathogen is eradicated.”

The need to remain vigilant extends well beyond hepatitis, he adds. “Detecting mutant strains is going to be an ongoing issue for every lab with many different microorganisms.”
[hr]

Anne Paxton is a writer and attorney in Seattle.