Antinuclear Antibodies are abnormal antibodies made by the body. They actually may not do anything to us. But the test for them can be very useful in diagnosing a number of rheumatological diseases. such as Systemic Lupus Erythematosus (SLE, Lupus), Sjøgren’s Syndrome, Scleroderma, and Mixed Connective Tissue Disease (mixed symptoms of all the above). It can also help with some non-rheumatologic diseases, like Polymyositis/Dermatomyositis, Autoimmune Hepatitis, and Primary Biliary Cirrhosis.
There are different ways labs report the results, depending on the method used. The best, and most common (recommended by the American College of Rheumatology) is the “indirect immunofluorescence test,” which reports results in titers (concentrations of antibody). The lowest titer starts at 1:40 (“1 to 40”), then goes up by doubling 1:80, 1:160, etc., as high as >1:640. More on this below.
When done by indirect immunofluorescence test, in addition to the titer, the ANA can also describe staining patterns. These may include terms like homogenous, speckled, nucleolar, centromere, and more. Staining patterns require a lot of lab tech labor time, so ordering them may cost significantly more. Each pattern used to be thought as suggestive of one or another disease, but current consensus is that such supposition was flawed. We never order the “ANA with patterns” any more.
The “solid phase” method for performing an ANA gives results as either Positive (= Reactive) or Negative (= Non-Reactive). This method may give false-negatives. Also, without a titer, it’s impossible to know how significant the test is as a whole, since there are lots of false-positives due to countless irrelevant factors that make no difference (maybe 30% of people in general have titers 1:40).
For Lupus, Scleroderma, and Mixed Connective Tissue Disease, we like to see a titer of 1:160 at least. Lower than that can be considered negative, essentially ruling them out. However, to convince us of a positive test, the titer should be 1:320 or greater. For the other conditions above, there are enough patients with them who test negative such that the ANA isn’t reliable, although a positive result is certainly suggestive.
Many people may have a positive ANA, even at high titer, without any disease at all. The ANA is thus useless for those without symptoms. It should never be used to screen family members of patients with the relevant illnesses, because it would be completely unreliable.