Which characteristic best describes the A3 subgroup?

• A. It shows mixed-field reaction with anti-A reagent and negative reaction with anti-A1 lectin
• B. It is the most common A subgroup
• C. It reacts with anti-A1 lectin
• D. It has no clinical significance

Answer: (A)

Recognize the pattern that identifies A3: mixed-field agglutination with anti-A and a negative reaction with anti-A1 lectin. This reflects the A3 subgroup’s uneven expression of A antigen, so some red cells react with anti-A while others do not, producing a mixed-field appearance. Anti-A1 lectin specifically detects A1 antigen; since A3 is not A1, there is no reaction, hence the negative result with the lectin. A3 is a non-A1 A subgroup and is not the most common A subgroup (A1 is). While it contains A antigen, its variable expression can lead to typing discrepancies, which is why recognizing this pattern matters for accurate transfusion decisions.