CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
Amy Carpenter Aquino
September 2019—The results of a clinical trial of a rapid assay for dual detection of HIV and syphilis were reported at the 2019 HIV Diagnostics Conference in March. If approved by the FDA, where it has been under consideration since 2018, the Chembio Diagnostic Systems assay would be the first point-of-care assay of its kind on the U.S. market.
“If we’re going to address the situations of infectious diseases throughout the world for most of the people in this world, we’re going to have to use rapid assays,” said Niel T. Constantine, PhD, MT(ASCP), professor of pathology, Institute of Human Virology, University of Maryland School of Medicine.
Dr. Constantine
Dr. Constantine, who is director of the institute’s laboratory of viral diagnostics, presented the findings of his evaluation of the Dual Path Platform HIV-Syphilis assay and Micro Reader, which provide results in 10 to 30 minutes with fingerstick, venous whole blood, or plasma.
For syphilis detection, a rapid assay with robust storage of up to 30°C is particularly advantageous, Dr. Constantine said, since the reference tests for syphilis—RPR (rapid plasma reagin) and TP-PA (T. pallidum particle agglutination)—require cold chain shipment and refrigeration. He called rapid tests for syphilis “probably the only appropriate tests that can be used in many places throughout the world.”
In 2015, the Standard Diagnostics Bioline HIV/Syphilis Duo assay, which is not available in the U.S., became the first HIV-syphilis multiplex test placed on the WHO list of prequalified in vitro diagnostic products. “Their evaluation showed pretty low sensitivity for syphilis at 87 percent,” Dr. Constantine said. “However, they felt it was important to have this in the market, mostly for pregnant women.” WHO recommends HIV and syphilis testing for a woman at least once, preferably in the first trimester, and backs the use of a dual HIV/syphilis rapid diagnostic test to “facilitate implementation of this recommendation.”
The 2017–2018 clinical trial of the Chembio DPP HIV-Syphilis system was part of the premarket approval Chembio submitted, Dr. Constantine said. He reported the results of one portion of the trial, which consisted of testing samples from two sites: the University of Maryland and the Fanno Creek Clinic in Portland, Ore. Data from the two sites were combined to show performance characteristics.
The DPP HIV-Syphilis kit box has 20 sample collection loops to collect about 10 µL of sample from fingerstick, plasma, or venous whole blood. A buffer vial dilutes the sample, and then the sample in the sample vial is added to the device. “It’s a typical lateral flow-type assay,” Dr. Constantine said. “In this case, it’s two wells with a dual path.” The sample-buffer combination goes in the bottom well, and after five minutes, four drops of buffer are placed in the upper well. “And you read the results.”
Results must be read with the DPP Micro Reader, which sits on top of the lateral flow device and reads the result in three seconds. “Press a button and get a result for HIV. Press it again and get a result for syphilis. Simple to use, very easy, very objective,” he said. “When faint lines occur, the DPP Micro Reader takes the guessing out of the equation.”
During the study, four tubes of blood were collected from each subject. “We had to centrifuge at least one of the tubes within two hours,” Dr. Constantine said, “and that was shipped to a reference lab for reference testing of HIV and syphilis.” Fingerstick, whole blood, and plasma were tested on site with the DPP HIV-Syphilis assay.
For HIV reference testing, the central laboratory used the CDC recommended algorithm, beginning with the fourth-generation Abbott Architect HIV Ag/Ab Combo assay, followed by either the Bio-Rad Multispot HIV-1/HIV-2 Rapid differentiation test or the Bio-Rad Geenius HIV 1/2 Supplemental Assay. If those results were discordant, RNA testing was done with the Hologic Aptima HIV-1 RNA Qualitative Assay.