Blood specimens for pretransfusion antibody screening should be no older than 3 days old. How is the "3 day rule" calculated?

In calculating the 3 days, the day that the blood specimen is drawn is counted as Day 0. For example:

  • Day 0 - sample drawn on Monday
  • Day 1 - Tuesday
  • Day 2 - Wednesday
  • Day 3 - Thursday (up to 23:59)

In effect, the sample can be used for up to 96 hours.