Bob Roehr
November 16, 2010 (Denver, Colorado) — The first generation of rapid screening tests for the hepatitis C virus (HCV) antibody, which use blood and oral fluids, underwent field testing in September at 4 sites: Dallas, Texas; Denver, Colorado; Seattle, Washington; and New York City. The tests had considerable variation in performance across the 4 test sites, with wide ranges in sensitivity, specificity, positive predictive value, and negative predictive value.
Bryce Smith, PhD, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and the project's team leader, presented the initial findings from 5 rapid test kits here at the American Public Health Association 138th Annual Meeting.
Three diagnostic manufacturers submitted 5 different test kits that used oral fluid, blood obtained from a finger stick, or both. The rapid HCV assays evaluated were the Dual Path Platform HCV rapid assay (Chembio); the Multiplo Rapid HIV/HCV Antibody Test (MedMira Laboratories); and the Hepatitis C Rapid HCV Antibody Test (OraSure Technologies).
The comparators were the currently approved standard assays: Abbott AxSYM anti-HCV microparticle immunoassay (Abbott), used in New York City and Seattle; ADVIA Centaur HCV Chemiluminescent Immunoassay (Bayer), used in Dallas; and HCV Version 3.0 ELISA Test (Ortho), used in Denver.
The confirmatory test for all was the Recombinant Immunoblot Assay HCV 3.0 SIA (Chiron).
"There was considerable variation in performance characteristics across sites and across rapid tests, with substantial ranges in sensitivity, Dr. Smith and colleagues report. Sensitivity ranged from 78.9% to 97.4%, and specificity ranged from 80.0% to 100%.
Dr. Smith said the sensitivity appears to be greater for blood than for oral fluid, but this round of evaluations was not powered to assess that difference.
"There was only 1 variable that predicted false results, and that was [coinfection with] HIV" — that occurred only with the oral test at the New York City site.
"We cannot compare these across cities at all," he said. "They all used different immunoassays, they were all different testers, they all had different participants, and they were all using different commercial labs with uniquely different protocols. But it does give us a sense of what the sensitivity and the specificity look like when we use these in the field."
"The most sensitive [kits] certainly are appropriate as a screening test for high-risk [people, such as those] who inject drugs," Dr. Smith noted. He envisions using them at syringe exchange and methadone treatment sites, health fairs, in military field operations, and elsewhere. He also believes they will be a more cost-effective alternative at low-volume sites.
Dr. Smith said they plan to start prospective studies of the rapid tests in March or April 2011, and should have preliminary data within the year. Already, the CDC "is talking within the division about how rapid testing can be integrated into our HCV testing algorithm." But that probably will not be finalized and publicly available until after the first test is on the market.
The OraSure rapid test has already been approved by the US Food and Drug Administration (FDA) for laboratory use with venous blood; the finger stick application is under FDA review. The company is conducting studies toward a CLIA (Clinical Laboratory Improvement Amendments) waiver, which would allow for nonlaboratory use of the screening test in the field by minimally trained staff.
Stephen R. Lee, PhD, OraSure's chief science officer, told Medscape Medical News that they have not yet submitted data on the oral swab version of the HCV screening test.
In a separate conversation with Medscape Medical News, Dr. Smith acknowledged that the case for rapid testing for HCV is not as strong as it is for HIV or other infections where there is significant forward transmission through sexual activity. He believes it will be most useful in situations like methadone maintenance programs, where there is "a case management element" to get people into care if they test positive for HCV.
He said 3 different groups are working on "an antibody/antigen test. Then you wouldn't just know that somebody was exposed, you would know that somebody was chronically infected." That will make a real difference in clinical practice, Dr. Smith explained, because with an antibody test alone, physicians "are not always inclined to follow up. But if somebody is chronically infected, they have to look at it harder."
Dr. Smith emphasized the importance of linking testing to care. This will be an important part of the CDC algorithm when it is released.
"You shouldn't be doing rapid testing if you cannot make sure that you can at least connect individuals with a medical evaluation of some sort, preferably that will involve a [polymerase chain reaction test], so that they can be assessed for chronic infection, and if they are, be referred for care," he said.
The CDC funded the studies in collaboration with local departments of health; the companies contributed test kits for evaluation. Dr. Smith has disclosed no relevant financial relationships. Dr. Lee is an employee of OraSure.
American Public Health Association (APHA) 138th Annual Meeting: Abstract 4024.0. Presented November 9, 2010.
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