Paternity Testing, Blood Types and HLA
Determining paternity and pin pointing the biological father of a child before the advent of DNA paternity testing was close to impossible. Blood typing had to be used or prior to that, the mother’s words and testimony. After all, the mother is always known but the father can be somewhat more difficult to pin point.
There have been many instances when strong scientific evidence has been required to determine the biological father of the child. Paternity definition works backwards from the child to the alleged father. The current day technology has reached a stage where 99.999% paternity inclusion can be reached through DNA testing. Polymerase chain reaction offers astounding levels of accuracy but it is only in the past 2 or so decades that this procedure has been available. But before the nature of genes came to be known to humans, techniques using blood groups were often employed for determining the true biological parent.
Blood typing for DNA testing
The preferred paternity blood test system is ABO typing. Although, the system is difficult to perform and does not give accurate results, it was the best known method during earlier days. It includes four blood types, namely A, B, AB and O. ABO antigens, proteins linked to red blood cells in the body, are inherited by the child from the parent.
These antigens can determine the blood type of the child, out of the given four types. Thus, if the blood type of the father and the mother is known, predicting the child’s blood type becomes easy. For example, if the mother carries a blood type of AB and that of the father is O, the child’s type can only be A or B.
This system of paternity testing has only 30% power of exclusion. It is highly useful in excluding a man as the biological father however, when seen the other way around, blood typing is highly inaccurate. Having the same blood type in both the father and the child doesn’t prove paternity and any man with the same blood group as the child could claim to be the father. Moreover, the child can have A, AB or B blood type for several combinations of mother’s and father’s blood types.
HLA testing for paternity
The era of 1970s marked greater success in determining paternity and advancement in science. Human Leukocyte Antigen (HLA) paternity blood testing method evolved at around this time, elevating the accuracy of paternity testing with blood types to an 80% power of exclusion, and in some cases to even 90%. HLA are common proteins found in most of the cells, especially white blood cells. Human body typically requires these HLA antigens for a stronger immune system.
Out of the many variations of HLA, every person inherits a unique set of these proteins from their parents. This led to a more refined type of paternity test with blood type, using both tissue and blood to find antigens, common in both the biological father and the child.
But, this procedure still falls short of providing an accurate result that is beyond question. It can separate a greater amount of false allegations but cannot differentiate and single out the alleged father, as some humans do have rarer types of HLA antigens. Also, this method cannot be used for children less than 6 months old as it requires a large amount of sample for testing. HLA testing is also expensive and time consuming.
Current scenario in paternity testing
Instead of relying on a paternity test with blood types, producing vague and less accurate results, DNA testing is now widely used to confirm the biological father. After the discovery of the DNA structure in the 1950s, blood groups and RFLP (restriction fragment Length polymorphism) became the standard methods but in the last two decades PCR method of DNA analysis was developed and is not the only method used. All other methods have fallen into disuse.