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.