The concordance of serial ANA tests in an Australian tertiary hospital pathology laboratory.

The antinuclear antibody (ANA) tests are some of the more frequently requested tests for the diagnosis of autoimmunity. Although they are used primarily as diagnostic blood tests, multiple requests on the same patient continue to be encountered in the laboratory. This retrospective analysis of serial ANA testing at one pathology laboratory in Australia is the first study that examines the statistical concordance and possible implications of this on clinical practice. High-titred ANA have quite good repeatability for titre and pattern, and low-titred ANA, which can be non-specific, have poor repeatability. Staining patterns are, in general, almost random in nature on serial tests when compared to the first-obtained ANA pattern for each patient. This study confirms that there is little benefit in serial ANA testing, and only if there is a clear change in the patient's clinical picture would repeat of an initial low-titred ANA be useful. The findings reinforce the need for pathology stewardship to minimise costs, wasted resources and unnecessary referrals.