Using Blood Types
as a Cheap Paternity Test

The earliest paternity test was a comparison of blood types. This analysis cannot provide absolute proof of fatherhood. But it can often eliminate a potential father. Plus, you may already know each person’s type from medical records. In that case the cost is zero.

TIP: If a man was ever in military service, his blood type will be on his dog tags.

Even if you don’t already have this information for everyone, blood typing is less expensive than DNA testing. So you may want to identify the missing blood types before you incur the expense of a DNA paternity test.

ABO Blood Groups

Briefly, here’s how blood typing works. There are four common blood types: A, B, AB, and O. If you know the mother and child’s blood types, then you can use the following chart to narrow the list of possible blood types for the father.

First, find the child’s type and the mother’s type in the chart. Then find the cell where the child’s column intersects the mother’s row. This cell shows the possible blood types for the father. If a man in question is not one of these, you can eliminate him as a possible father.
For example, if the child is A and the mother is O, the father MUST be A or AB. It is biologically impossible for a man with B or O blood to have fathered this child.

NOTE: The two blank cells represent impossible combinations between mother and child, regardless of the father.

Important Limitations

As you can see in the chart, there are some combinations of mother and child that show all four possibilities and cannot, therefore, eliminate any possible father.

The most important limitation is that knowing this information can, at best, only eliminate someone. By itself, it cannot prove that any given man is the child's father.

However, if the mother knows there are only two possible candidates, eliminating one of them will tell her that the other one is the father.

If this doesn’t resolve the question—-or if you need a positive paternity test for legal purposes—-you must still go the paternity test DNA route.

Return from Blood Types to Paternity Test Intro

Return to DNA Testing Home