GAST and episodic ataxia type 2: Although serum gastrin levels and the presence of APCA are complementary tests for the diagnosis of AIG, the occurrence of APCA was not deemed essential for verifying AIG, as up to 20% of patients are not seropositive.24 There are some non-invasive serological markers for the diagnosis of AIG that should be ordered before gastroscopy and biopsy.