In classification, common features are most important, said Dr. Aringer. Although each lupus patient is unique, all have autoantibodies to nuclear antigens (ANA), as well as many other autoantibodies, and evidence of immune complex deposition from histology to complement to interferon signature. This leads to many different organ manifestations in SLE.
“ANA has very high sensitivity, but its specificity is actually pretty low. For anti-Smith antibodies, it’s the other way around. So it doesn’t make sense to have them side by side in the criteria,” said Dr. Aringer. They hypothesized that ANA would be the entry criterion and then tested if that was feasible.
Many conditions have overlapping features with SLE, “but if two of these attributes are found together, especially in a patient who also has autoantibodies, it’s usually SLE,” he said.