The Antinuclear Antibody (ANA) test

Posts copied from the NICE guidelines thread here

I'm fascinated by this comment by Royal United Hospitals Bath NHS Foundation Trust (https://www.nice.org.uk/guidance/ng206/documents/consultation-comments-and-responses-2, page 292):

Could these "false positive results" indicate that immune disturbances (those which don't meet the threshold for a formal autoimmune diagnosis) are more common than we think?

 

It's probably a reference to an ANA test, which can have a pretty high false positive rate: https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Antinuclear-Antibodies-ANA

 

This area is very complicated but basically these are not 'false positive' results. A positive ANA is a real biological phenomenon, unless your lab is below standard. What is meant is that a positive ANA does not necessarily indicate lupus because a proportion of healthy people have positive ANA. But then a proportion of those go on to have lupus and other things.

Autoantibody tests are only a problem if they are interpreted by people who don't understand diagnostic processes. Sadly, quite a high proportion of medics fall into that category. But having diagnosis of 'possible lupus' does less harm than failing to identify lupus by deliberately not doing an ANA.

 

Yes, that was exactly what i was thinking. You can't decide anything's a "false positive" unless you have a second, well-validated measure of the same phenomenon against which to compare it. "False positives" in this type of setting mean positives that don't align with any known disease profile.

Obviously, something as simple ANA levels is not going to be a reliable biomarker of ME or anything. But we are doing ourselves no favours by dismissing these things as "false positives" using totally circular reasoning.