Paternity testing using ABO blood types is impossible

A man sent us an email over the weekend because he wanted to know if he was the father of a child. He hasn’t taken a paternity test yet, but he knows the blood types of himself, the mother and the child. Based on those blood types he wants to know if he can still be the father. Surely this man is not the only person with this question, so I’ll answer the question publicly.

Blood type antigens are inherited from the father and the mother. Depending on the blood types of these individuals it is sometimes possible to exclude an alleged father. However, it is never possible to prove paternity. Blood typing, based on the ABO blood group system is not an accurate method for determining paternity.

Blood typing is useful for predicting potential paternity situations, but it is not useful for a legal determination of paternity.

This specific case is as follows:

Potential Father: O

Mother: B

Child: AB

Using the chart to the right, we can determine that the potential father is excluded from being the father. ABO blood typing can exclude roughly 30% of the male population from being the possible father.