I'm giving a talk to some local GPs tonight. My talk's title is:
"How to interpret a positive ANA? Is it worth measuring?"
A common presentation to rheumatologists involves a person who has had this test, ANA (anti-nuclear antibody) measured. When the result returns positive, it can be quite hard to interpret.
This is due to the test being non-specific. Many people without disease can have a "falsely" positive result.
This test is really only useful if the pre-test chances of the patient having a related disease is reasonably high. In this case, the positive results increases the probability of disease and helps with making a more certain diagnosis.
When the pre-test chance of having the disease is slim, a positive result becomes confusing. It adds a layer of anxiety for patients especially when they search the net regarding the ANA. What the person will invariably read about will be lupus.
Many patients who see me with a positive ANA don't have lupus or any other related disease. In these cases, it may be an incidental finding and my job is to reassure them and reduce anxiety.
I usually draw to help them understand. I added these diagrams to my talk tonight but I thought I'd share them.
There are many people walking around with a positive ANA. The X represents the patient sitting in front of me with the incidental finding of a positive ANA.
Some people with a positive ANA will have symptoms related to the ANA. A smaller number of these will actually have enough features to make a diagnosis of a classifiable disease.
Yes, some people with a positive ANA may in time develop symptoms related to it, and some may indeed develop an autoimmune disease related to the ANA, but this is the minority. Even if it does develop, it may take many, many years with the important point that people should just lead normal lives and not worry excessively about a positive blood test.
I hope these drawings in some way help me convey the message.
What do you think?