C4A and vitiligo: Patients with vitiligo have also been found more likely to have AITD when their immunoglobulin plus complement tests (IgA, IgG, IgM, C3, and C4) were abnormal, when they had thyroid nodules or tumors, and also when the Positive and Negative Affect Schedule (PANAS) assessment registered negative emotions (12, 23, 24).