Point-of-care HCV RNA test shows good accuracy

Last Updated: 2017-05-17

By Scott Baltic

NEW YORK (Reuters Health) - A point-of-care test that can detect active infection with hepatitis C virus (HCV) from a finger-stick sample and provides results in less than two hours showed good sensitivity and specificity in a multicenter Australian study.

The Xpert HCV Viral Load test (Cepheid, Sunnyvale, Calif.) represents an advance over current antibody-based tests, which indicate only past exposure to HCV. The test can detect HCV RNA in capillary whole blood collected by finger-stick and in plasma collected by venipuncture.

The open observational cohort study was conducted at five sites: three drug and alcohol clinics, one homelessness service, and one needle and syringe program.

�€œThe results from this study are encouraging, given that the performance of rapid diagnostic tests in clinical settings is poorer than in the laboratory,�€ the researchers wrote in a paper online April 21 in The Lancet Gastroenterology and Hepatology.

Given that 25% of people will spontaneously clear their HCV infection, �€œthe availability of a point of care test to detect active HCV infection represents a major advance over previous point of care HCV tests, which only test for exposure to the virus,�€ corresponding author Dr. Jason Grebely, of The Kirby Institute, University of New South Wales, Sydney, told Reuters Health by email.

�€œWe need to continue to move towards low-cost, rapid tests for detecting active HCV infection, because in many countries the cost of screening large numbers of people will be a big barrier towards large improvements in HCV diagnosis,�€ he added.

�€œSensitive HCV RNA testing of whole blood collected by finger-stick is particularly appropriate for populations with a high prevalence of HCV infection,�€ such as the individuals in this study, he said. �€œOften these people are highly marginalized, so having an opportunity to engage people in testing, linkage to care, and treatment in a single visit may reduce drop-outs along the HCV cascade of care.�€

Dr. Grebely cautioned, however, that the test is not yet approved in many countries and that further studies are needed to evaluate the assay in different settings and populations, such as patients given direct-acting antiviral therapy, those with a sustained virological response, or those with HIV/HCV co-infection.

In an accompanying commentary, Dr. Curtis Cooper of the University of Ottawa, Ontario, Canada cited some of the substantial obstacles that keep HCV-infected individuals from accessing care, including the shortcomings of current diagnostic tests. He explained that rapid HCV RNA testing can reduce the impact of these barriers.

Though not ideal, a turnaround time of less than two hours, he writes, �€œmitigates the problem of patients not returning to the testing site for their results, and the waiting time can be used for HCV education and harm-reduction activities . . . Given the transient nature of many people living with HCV (who are often lost to follow-up), rapid testing enables immediate action while the patient is temporarily engaged in the health-care system.�€

Dr. Raymond Chung, director of hepatology at Massachusetts General Hospital, Boston, noted in a phone interview that the Xpert HCV Viral Load point-of-care test doesn�€™t rely only on antibodies.

The sine qua non of HCV diagnosis, he said, is the detection of viremia in the form of HCV RNA, but such a point-of-care test has been lacking until now. It�€™s �€œa potentially field-ready test�€ and could be especially important in low- and middle-income countries.

Though refinements still needed, and it would be ideal to shave the time down, so the patient could leave with a care plan in place, Dr. Chung said, �€œIt�€™s a good start.�€

The study recruited participants age 18 or older and either with a history of injection drug use or recruited from the homelessness service. The final analysis population of 150 participants had a median age of 44. Most patients (130, or 87%) were male.

The sensitivity of the Xpert HCV Viral Load assay for HCV RNA detection in plasma collected by venipuncture was 100.0% and specificity was 99.1%. The assay�€™s sensitivity for HCV RNA detection in samples collected by finger-stick was 95.5% and specificity was 98.1%.

The Abbott RealTime HCV Viral Load RNA assay was used as the gold standard against which the Xpert HCV Viral Load was compared.

A modified Xpert HCV Viral Load assay is under development with a time to result of 60 minutes.

The study was funded by the National Health and Medical Research Council (Australia), Cepheid, the South Eastern Sydney Local Health District (Australia), and Merck Sharp and Dohme (Australia).

Dr. Grebely has received research grants from Cepheid; two authors are employees and have equity interests in Cepheid.

SOURCE: http://bit.ly/2qTabw6 and http://bit.ly/2pUMi3r

Lancet Gastroenterol Hepatol 2017.