The antinuclear antibodies (ANA) test--indirect immunofluorescence (IIF) assay on HEp-2 cells--is the standard blood test (ANA-HEp-2) used to detect ANA, the presence of which indicates the possibility of autoimmunity. However, a false positive ANA occurs in up to 13 percent of healthy individuals. Now a group of Brazilian researchers have uncovered distinguishing characteristics of the ANA test in healthy individuals and in patients with autoimmune disease. This finding reduces the likelihood of an erroneous autoimmune disorder diagnosis.

     Research team leader Luis Andrade, M.D., Ph.D., of the Federal University of Sao Paulo, Brazil, reported that the team recruited 918 healthy individuals (634 females and 284 males) between the ages of 18 and 66 years old. The control group was comprised of 153 patients with autoimmune rheumatic diseases--lupus, systemic sclerosis, Sjögren's syndrome, and idiopathic inflammatory myopathy. To determine the concentration of ANA in the blood, ANA-HEp-2 tests were run on all participants. The tests were considered positive if a well defined IIF pattern was identified.

     Researchers determined that positive ANA-HEp-2 tests in healthy participants occurred mainly as a nuclear fine speckled (NFS) pattern, at low to moderate titer, or as a nuclear dense fine speckled (NDFS) pattern, frequently at high titer, in 46 percent and 33 percent of ANA-positive healthy individuals, respectively. Healthy participants did not present a nuclear coarse speckled (NCS) or a nuclear homogeneous (Ho) pattern.

     In participants with autoimmune disease, the ANA-HEp-2 showed positive results at a predominantly moderate to high titer. Researchers observed a distinct ANA-HEp-2 pattern profile, characterized by the absence of the NDFS pattern and the exclusive occurrence of the NCS, centromeric, nuclear homogeneous, and cytoplasmic dense fine speckled patterns. ANA-positive patients with confirmed autoimmune diseases showed the presence of the NFS pattern at a higher titer than in healthy individuals.

     Dr. Andrade concluded, "Our study confirms that the ANA-HEp-2 pattern is critical in properly diagnosing autoimmune disorders, and future research should attempt to reproduce the interpretation of test results among different ANA experts and ANA-HEp-2 slides brands."

--Source: "Accurate interpretation of antinuclear antibodies test key to confirming autoimmune disease," EurekAlert, R&D News, January 5, 2011