Exagen Inc. operates as a commercial-stage diagnostics company, develops and markets products for the diagnosis, prognosis, and monitoring of patients affected by autoimmune rheumatic diseases (ARDs). Its lead product includes Avise SLE+CT, a proprietary diagnostic test that provides an enhanced solution for patients with a range of ARDs, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjögren's syndrome, and scleroderma, as well as other disorders, including fibromyalgia. The company also offers Avise SLE Prognostic, a blood test that complements Avise SLE+CT; Avise MTX, a therapeutic drug monitoring test to measure levels of methotrexate polyglutamates; and Avise HCQ, a blood test for physicians to monitor blood levels of HCQ. In addition, it is developing Anti-TNF, a blood test to monitor the levels of anti-TNF bioactivity in patients with RA; Avise SLE Monitoring, a multi-analyte panel blood test for physicians to track the disease status of their SLE patients; and Avise RA, a blood test to determine bone damage or joint erosion. The company primarily serves rheumatologists in the United States. It was formerly known as Exagen Diagnostics, Inc. Exagen Inc. was incorporated in 2002 and is headquartered in Vista, California.