CD40LG and alkaline phosphatase measurement: To aid in the determination of the cause of his AP, an extensive workup including anti-neutrophil antibody (ANA), cytoplasmic antineutrophilic cytoplasmic antibody (c-ANCA), perinuclear antineutrophilic cytoplasmic antibody (p-ANCA), anti-mitochondrial antibody, complement components 3 and 4 (C3, C4), complement total (CH50), immunoglobulin G4 (IgG4), Mycoplasma IgM, HIV, Cytomegalovirus IgG and IgM, Coxsackie, COVID-19, hepatitis A, B, and C, ceruloplasmin, alpha-1 antitrypsin, IgG4, and ferritin were done and were unremarkable.