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), Sjgren'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