1. Check the age of the patient
2. Repeat the ABO group at 4°C [anti-A and anti-B react best at 4°C].
3. QC required: because all persons have a harmless autoanti-I reactive at 4°C, include an autocontrol. (Autoanti-I may agglutinate the A₁ cells, the B cells, and the patient's own cells at 4°C.)

---

©1999 Division of Medical Laboratory Science
University of Alberta

---