Standard 5.13.5 in the 27th is Comparison of patient's previous test results for ABO group and Rh type in last 12 months if comparison is not performed electronically. That retention was 5 years however standard 5.13.5.2 for Difficulty in typing, clinically significant antibodies; etc was indefinite. In the 28th edition, 5.13.5 includes reviewing historical records for the following ABORh, difficulty in typing, clinically sig ab, significant adverse event and special transfusion requirements (merging std 5.13.5, 5.13.5.1, and 5.13.5.2 together). The new record retention period was changed in the 28th edition on Nov 1st to 10 years. Hope that helps!