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XMRV: still waiting for a test
Friday 24 December 2010
XMRV: Still Waiting For a Test
Earlier this week, an FDA advisory panel recommended that the agency bar people who report a diagnosis of chronic fatigue syndrome from donating blood amid concerns about a possible link with the virus XMRV.
But reliably testing potential blood donors or people with CFS for XMRV isn’t yet possible.
That’s the conclusion from the latest phase of an ongoing study launched by the HHS Blood XMRV Scientific Working Group, which was set up last year after a paper in Science linked XMRV to CFS. An update on the study was presented to the FDA advisory panel and again today on a webinar sponsored by the CFIDS Association of America, a patient advocacy group.
Many groups are racing to develop an XMRV test in case it turns out that potential blood donors need to be screened for XMRV. But in a presentation on today’s webinar by Graham Simmons of Blood Systems Research Institute, the lab that has been coordinating the working group studies, one of the slides summed it up: Participating Labs — Discordant Results.
The first phase of the study evaluated the performance of XMRV tests developed by a number of labs, including the Whittemore-Peterson Institute (which first found the XMRV link to CFS), the CDC, FDA, and National Cancer Institute, among others. All the tests did very well when looking for XMRV in blood samples that had been spiked with it.
But in the second phase of the study, which had a subset of the labs look at clinical blood samples from four people who tested positive for XMRV in the Science study, things didn’t go as smoothly. In round one of this second phase, the CDC and the WPI labs were able to find XMRV in the plasma of at least some of the patients. The NCI lab did not find any positives, despite having a very sensitive test. So, they decided to do it all over again in the hopes of confirming the findings. “Instead it went in the opposite direction,” Michael Busch, director of Blood Systems Research Institute, tells the Health Blog.
When the same four people gave blood again, the three participating labs — plus a fourth commercial one — didn’t find XMRV in any of the plasma samples.
Some of the possible reasons why were discussed on the webinar. The number of people involved was tiny, and it turns out that one of the four actually does not have a CFS diagnosis but was a family member of someone with CFS. Another one of the four started taking anti-retroviral medication around the time her blood was drawn, which also could have impacted the results. Or, it’s possible that the amount of virus present varies over time and was low when these samples were taken.
So what’s next? Phase 3, which is going to include much larger numbers of CFS patients (30) and even larger numbers of healthy controls (40-50), say the working group scientists. More commercial labs are likely to be brought in to do testing. Blood will likely be drawn in January, with results in possibly three months later. “It is a frustrating process,” Busch says, “but we are staying the course and moving to Phase 3.”
The above originally appeared here.
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