PoM No 6,2013

Publication of the Month

June 06/13: Usefulness of a positive ANA test result in a clinical practice. 

Key messages:  

  • A positive ANA test result has very low correlation with actual rheumatic disease in primary care referrals
  • ANA test ordering is often made for inappropriate reasons and more careful pre-test consideration would decrease unnecessary testing and improve the usefulness of the results

 Abeles AM, Abeles M.
The Clinical Utility of a Positive Antinuclear Antibody Test Result
Am J Med. 2013; 126:342-348.

Background: Many studies have investigated the frequency of ANA positivity in the general population. This study differs in that it was performed by clinicians reviewing the records of 232 patients referred to them over a 2 year period for a positive ANA test result. The authors wanted to evaluate the “real world” clinical usefulness or otherwise of such a result and collated all relevant clinical and laboratory data as well as the initial reasons for ordering ANA testing and the ultimate diagnosis.

Summary: 85% of the referrals in this study were from primary care providers. The most common reason for ordering ANA testing was widespread pain and tenderness. No patients with an ANA titer <1:160 had an ANA-associated rheumatic disease and the overwhelming majority of patients who did have an ANA-associated rheumatic disease had an ANA of > 1:640. However, even using a titer of 1:160 as a cut-off value, the positive predictive value (PPV) for ANA positivity was still only 11.6% for any ANA- associated rheumatic disease.

Conclusions: A positive ANA only occasionally (less than 10% at a cut-off titre of 1:40) implies the presence of an ANA-associated rheumatic disease in clinical practice. ANA testing is overused as a screening tool, often in clinical presentations that do not suggest connective tissue disease and can potentially lead to adverse consequences.

Comment: This paper looks at ANA testing in a real, clinical setting from the perspective of the rheumatologist to whom these patients are referred. The authors do not discourage primary care physicians from requesting ANA testing but they do suggest more careful consideration of presentation before the test is ordered. In light of their findings, they urge labs to share their data on the background rate of ANA positivity with primary physicians and suggest appropriate counselling of patients as to the non-likelihood of actual disease association with a positive result. Many clinicians are not aware of the low association between ANA positivity and actual rheumatic disease and discussions over the relevance (or lack thereof) of such a test result have the potential to improve the usefulness of the test to both patients and providers and also to reduce the financial and social/emotional costs of unnecessary testing and its consequences.

 

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.