This is a brief bullet point summary of the detailed Technical Article on Scleroderma ANA and Antibody Testing. It is intended primarily for physicians / nurse practitioners that are doing initial screening of patients for a possible diagnosis of scleroderma.
The American College of Rheumatology, in a 2011 Position Statement, recommends that ANA testing by indirect immunofluorescence (IFA) “should remain the gold standard for ANA testing”. This is especially important when doing initial ANA and antibody screening for patients that may have some form of scleroderma.
Historically, all ANA testing was done by IFA. Now, however, most ANA testing is (by default) done using newer, less expensive methods such as ELISA or Multiplex. ANA testing by IFA can detect up to 150 different antigens. Typically, ANA testing by ELISA detects 8 to 10 antigens and testing by Multiplex detects 11 to 13 antigens.
ANA testing by ELISA or Multiplex is very accurate IF the patient has one of the antibodies included in the panel. However, if the patient has an antibody that is not included in the testing panel, the ANA result itself will be falsely reported as negative, suggesting that the patient does not have an autoimmune disease.
While all scleroderma-specific screening panels will include the two main antibodies that have been linked to Scleroderma for decades: anti-Scl70 (associated with diffuse scleroderma) and anti-centromere (associated with limited scleroderma), these panels commonly leave out a number of other antibodies that have been linked to scleroderma based on recent research. In one recent study, a typical scleroderma screening panel done by Multiplex resulted in an almost 43% false negative rate since these other antibodies were not included in the panel. Notably, one of these antibodies – anti-RNA polymerase III – has an incidence rate of about 20%, comparable to the general rates for the two main scleroderma antibodies.
Unless you know specifically that an ANA / reflex scleroderma antibody screening panel includes almost all of the (ten) documented scleroderma-related antibodies, if you get a negative ANA result and it was not done by IFA, then it is critically important that you confirm the negative ANA result by re-running the ANA using IFA. (Note: since ANA testing by IFA can miss anti-centromere antibodies if not done with human (HEp-2) substrate, it is important to verify that the ANA IFA test is done using HEp-2. This should not be an issue in the US but may be elsewhere.) Ordering the confirming ANA by IFA is particularly important if you are ordering a general rheumatic screening panel rather than a scleroderma-specific screening panel because the patient’s symptoms are not specific enough to point to one specific autoimmune disease. Some general rheumatic screen panels do not even include anti-centromere antibodies, and it is extremely unlikely that any of the “newer” scleroderma-specific antibodies would be included in the panel, given the limited number of antigens that can be included in the panel when run by either ELISA or Multiplex.