We report herein a case of Factor XIII deficiency that remained undiagnosed until 2 years of age. Part of the delay in diagnosis was a consequence of testing that was performed on a blood sample obtained after plasma transfusion therapy for a life-threatening bleeding episode. Due to insufficient family follow-up after discharge from the hospital, the diagnosis was delayed 1 year until the child was rehospitalized and a pre-transfusion plasma sample was tested. The commonly accepted approach of using only a qualitative test for the diagnosis of factor XIII deficiency is challenged by this case report.