Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (722 page)

   Evaluating patients suspected of having a systemic rheumatic disease

   Interpretation

Increased In

   SLE

   Drug-induced SLE

   Lupoid hepatitis

   MCTD

   Polymyositis

   Progressive systemic sclerosis

   RA

   Sjögren syndrome

   Limitations

   Some patients without clinical evidence of an autoimmune disease or a systemic rheumatic disease may have a detectable level of ANA. This finding is more common in women than in men, and the frequency of a detectable ANA in healthy women >40 years old may approach 15–20%. ANA may also be detectable following viral illnesses, in chronic infections, or in patients treated with many different medications.

   The traditional tool used to detect ANAs is IFA, which is a labor-intensive microscopic technique. Test interpretation is operator dependent. This assay is considered the gold standard for ANA testing with greater sensitivity. The IFA testing is currently performed using Hep-2 cells, and they contain approximately 100–150 possible antigens, and most of them are not well defined and/or characterized. When performed with a history and physical examination, it identifies almost all patients with SLE (95% sensitivity), although the specificity of this assay is only 57%. In addition, ANA by IFA has the sensitivity of 85% for systemic sclerosis, 61% for polymyositis/dermatomyositis (PM-DM), 48% for Sjögren syndrome, 57% for juvenile idiopathic arthritis, 100% for drug-induced lupus, 100% for MCTD, and autoimmune hepatitis (60%), as well as being important in monitoring and assessing prognosis in individuals with the Raynaud phenomenon.