There is no single diagnostic test for MAS, but doctors use a combination of medical history and symptom assessment, biopsies (if skin or intestinal conditions are involved), imaging tests (X-rays, MRIs, or ultrasounds to assess joint and organ damage), and blood tests for autoimmune markers. In addition to a full thyroid panel (TSH, Free T3, Free T4, TPOAb, TgAb), tests may include ANA, RF, anti-CCP, celiac panel, CRP, ESR, and vitamin/nutrient levels.