The sensitivity of the current ACR diagnostic criteria for scleroderma is only 34%, and most of the patients diagnosed according to this criterion already have significant visceral involvement (e.g., pulmonary fibrosis) and miss the best time for treatment. Early diagnosis and treatment of scleroderma is the key to improving its prognosis, so the EULAR Scleroderma Trial and Research Group (EUSTAR) proposed the diagnostic idea and diagnostic criteria of “very early scleroderma”, i.e., the “3 red flags” and the “2 tests”. “The diagnosis is divided into 2 stages. 1. Suspicion stage If the patient has the three manifestations of Raynaud’s phenomenon, finger swelling and positive antinuclear antibody (ANA), “very early scleroderma” should be highly suspected. These three signs are known as the “3 red flags”. 2. Diagnostic stage The above patients are further examined by capillary microscopy and scleroderma-specific antibody test (anti-Scl-70 antibody and anti-focal point antibody), and those with positive results are diagnosed as “very early systemic scleroderma”. These tests are known as the “2 tests”.