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Abstract Background and objectives: ABO phenotyping is one of the essential tests in Immunohematology. Incompatible blood group transfusion leads to acute hemolysis reactions and other serious complications. Anti A1 is a cold Antibody with no clinical significance, but if it is reacted at 37˚c can be clinically significant, which will be happened rarely. At the present, we report a Case with anti A1 having clinical significance and Anti C. Material and methods: The patient was suffering from Paroxysmal nocturnal hemoglobinuria (PNH) and received repeated blood transfusion. The tests performed for this patient were blood grouping, Antibody screening, panel test and cross match. Result: the patient’s blood group is AB (A2B) with anti A1. The presence of anti C is verified by applying Panel test. Conclusion: to prepare appropriate blood, Cross mach test was performed on A2B blood bags without C Antigen. During laboratory tests and blood transfusion, no reaction was observed. This report indicates that being aware of anti-antigen antibodies is an important point. Key words: Anti C and Anti A1 with Clinical importance, PNH, Ab Screening