A 26-year-old woman develops a red rash over her cheeks and pain, and swelling in both wrists as well as several small joints in her hands. The rash gets worse on sun exposure and involves her cheeks, nose, ears, and chin. Medical evaluation reveals oral ulceration and 3+ proteinuria. Which of the following is the most specific test for diagnosis of this condition?
High-Yield Explanation
Anti-Sm detects a protein complexed to six species of small nuclear ribonucleic acid (RNA). It is believed to be very specific for SLE. However, only 30% of patients have a positive test. In the case presented, there are enough clinical criteria (four) to confirm the diagnosis of SLE with 98% specificity and 97% sensitivity.