Blood test for Long Covid

New test for Long Covid

The Times reports on a diagnostic test from US-based diagnostics company IncellDx which claims to detect Long Covid and can distinguish between this and ME/CFS. The article is behind a paywall but can be accessed from the link below


Apparently, this simple blood test, which was recently approved by European regulatory bodies and has been launched on the Continent, uses artificial intelligence to measure inflammatory markers in the blood — small proteins called cytokines and chemokines — patterns of which may be specific to the illness. The test, the company claims, provides greater than 90 per cent accuracy, and can even, it says (although details of this remain vague), differentiate between long Covid and similar conditions such as ME/CFS (sometimes called chronic fatigue syndrome) and Lyme disease….

Some experts are sceptical, though. Jonathan Edwards, a professor at UCL and expert in autoimmune diseases, says: “The immediate problem with these profiles is that they are generated by machine learning, which maximises the chances of throwing up something unreproducible and irrelevant. It is also worth noting that in mainstream medicine, dealing with long-term inflammatory and autoimmune disease tests on cytokines like this have been essentially useless.”

“I am pretty certain there is no reliable evidence for efficacy [for these drugs in this context],” Edwards says. “We used to try things out ad hoc 40 years ago but we know enough now to know that we shouldn’t. Drugs are toxic. Unless you’ve tested in a controlled, double-blind setting, you don’t begin to treat people.”

However, he adds that “one can never dismiss anything totally since very unexpected beneficial effects have historically been confirmed — for example, chloroquine for rheumatoid arthritis.”

Comment from Dr Charles Shepherd

From the very limited amount of scientific information available about the background to this test I would fully agree with the reservations being expressed by Professor Jonathan Edwards. For a blood test to be used for diagnostic purposes it has to have a high degree of both sensitivity and specificity.

In other words:

  1. Does this test provide a clear positive result in a very high percentage of people who have a clinical diagnosis of Long Covid?
  2. Has it been confirmed that the test is only positive in people who have Long Covid and that it does not give positive results in people with inflammatory or infective conditions that have similar symptoms or immune function abnormalities?

Researchers have been trying to find a diagnostic test for ME/CFS for many years and although some progress is being made we still do not have one. So while this development is clearly of interest I think we have to be very cautious about concluding that there is now a reliable diagnostic test for Long Covid.

Dr Charles Shepherd,
Trustee and
Hon. Medical Adviser
to the ME Association.
Member of the 2018-2021 NICE Guideline Committee.
Member of the 2002 Independent Working Group on ME/CFS.

Dr Charles Shepherd
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