Interpreting ANA results

The type and nature of autoantibody testing and the way results are reported varies between local laboratories.

The most useful ANA result is a negative test as this makes it unlikely that the subject has an autoimmune connective tissue disease.

Other ANA results are often expressed as a maximum dilution titre, though some ELISA assays may give results in international units(IU).

• a titre in the range of 1:40-1:80 is usually reported as a positive test, though patients rarely have active autoimmune disease and interpretation of the result relies heavily upon the clinical situation
  • if however a patient is complaining of a photosensitive rash/or arthritis and is found to have an ANA of 1:80, that result is likely to be highly significant (1)
    
• a titre greater than 1:160, however is more likely to be significant and one may then go on to explore dsDNA or ENA tests.

A significantly positive ANA, in the absence of clinical evidence of connective tissue disease does not mean disease is present, though a proportion of these individuals may later develop an autoimmune syndrome.

Reference:

1. Pulse (2004), 64 (2), 63.