HCV Fingerstick Assay Results Dependent on Viral Load

An assessment of the Xpert HCV viral load fingerstick assay (Xpert HCV VL FS), a point-of-care test quantifying hepatitis C virus (HCV) RNA showed that median time to HCV RNA detection was dependent on HCV RNA level. Though not yet a part of the platform, investigators believe a faster time to diagnoses may be achieved by monitoring the time when HCV RNA is first detected with Xpert HCV VL FS, rather than HCV RNA quantification. These results were published in The Journal of Infectious Diseases.

The time to detection of the assay was evaluated using fingerstick whole-blood samples collected from participants in an observational cohort in Australia. A total of 1386 participants who were enrolled had a valid Xpert HCV VL FS testing result. In 23% of these individuals was detected.

In participants with undetectable HCV RNA the median time to result was 57 minutes. In those with detectable viral RNA the median time was 32 minutes and 80% of these patients had a detectable HCV RNA result in <40 minutes.

Investigators highlighted that although diagnosis could be inferred by monitoring time at which RNA is detected, in its current format, the assay must be completed before diagnosis is made. They further added that “there are a number of limitations with this approach and the results should not be provided until the assay has completed.” First, use of a detectable result prior to assay completion is an off-label use of the test in a manner not approved by regulatory authorities. Also, the use of such a test off-label would require careful considerations around appropriate counseling for those suspected of having HCV RNA.

Furthermore, each cartridge is a standalone assay and there are fluctuations of 5 to 6 minutes in the high and low internal quantitative standards between different participants. HCV RNA levels are assessed by quantitation parameters built into each cartridge and the exact threshold for detection is specific to each lot and not known to the operator. This information is only available after completion of the assay. Therefore, it is critical to have a trained operator familiar with the software and someone trained in post-test counseling.

In the future it will be important to explore how the current Xpert HCV VL FS test might be modified to facilitate a more rapid time to diagnosis, noted the investigators.  This evaluation was also limited by a low number of samples and HCV genotyping was not performed. This study was also performed by an experienced operator and may not reflect the observed real-world clinical setting.

This was however, according to investigators, the first proof of concept that this assay could be modified to provide a more rapid diagnosis. The availability of such an assay would be a significant improvement over exiting point-of-care assays and reduce wait times and improve linkage to treatment.

Reference

Grebely J, Catlett B, Jayasinghe I, et al. Time to detection of hepatitis C virus infection with the Xpert HCV Viral Load Fingerstick Point-of-Care Assay: Facilitating a more rapid time to diagnosis [published online January 29 2020]. J Infect Dis. doi:10.1093/infdis/jiaa037