The Antinuclear Antibody (ANA) test

[Woolie]

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):

At present the diagnosis is one of exclusion of other conditions. There are some tests which are not currently included, which should be considered for inclusion, particularly to reveal a treatable cause. Examples could be Vit D, Lyme serology, EBV markers of persistent infection, B12/folate, Magnesium. Autoimmune screening needs to be carefully considered as false positive tests often result (I would suggest only requested on clinical grounds. The evidence (or lack of it) regarding non-validated tests for factors such as mitochondrial function and ATP levels should be clearly stated.

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?

 

[petrichor]

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

 

[Jonathan Edwards]

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?

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.

 

[Woolie]

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.

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.