How does DNA testing differ from simply testing Blood to determine paternity?

There is an enormous difference, between both process and outcome in testing Blood for Paternity analysis, compared to testing DNA. Testing the blood of the child, mother and alleged father is generally of limited benefit, and will often result in an inconclusive outcome, and provide no clear cut answer.

Prior to the introduction of DNA testing as the norm for establishing paternity, a multitude of blood test were used to help determine paternity. In combination as a battery of tests, they provide some useful information, but never really got to the point of provide conclusive 'yes' or 'no' outcomes.

The test normally involved taking a blood sample from the alleged father and child, and carrying out both immunological and enzyme based blood grouping tests. For example the ABO blood typing test would provide the blood type of the alleged father and child. The interpretation of the results were generally carried out by specialists that understood the inheritance patterns of these blood types.

The results were complex to determine, and have over the past 15 years, been completely replaced by DNA based Paternity analysis, with it's much higher degree of reliability.