How to Read Paternity Test Codes

By Jimmy Boyd

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DNA test results can determine if a man is the father of a child. A lab conducts paternity tests and releases a report of the results. The untrained person often has difficulty understanding the results. The reports use paternity test codes to represent certain aspects of the test. A person involved in the testing needs to know how to interpret the results. Those who understand the results of the paternity test can use that knowledge when discussing paternity issues or participating in a lawsuit.

Step 1

Refer to a sample test report when learning how to interpret paternity test codes. A person involved in a real test can use actual paternity results from a DNA lab.

Step 2

Understand the meaning and purpose of the genetic systems. Paternity tests are actually a series of tests. Each test represents a region of the chromosomes of the mother, father and child. The two codes in each genetic system represent a genetic locus. A genetic locus exists for one chromosome from the mother and one from the father. The code is the name of the genetic region (locus) in the chromosome.

Step 3

Look at the allele sizes for each genetic system to see if a child matches both the father and mother. Alleles represent the size of the locus. The number codes represent that size. A genetic system is a match if the child has one allele identical to the father and one to the mother.

Step 4

See if there is a match for every genetic system to determine if the overall result is an "inclusion." An inclusion means that the man is not excluded as the potential biological father of the child. Any genetic system that does not show a match results in an "exclusion" result for the whole paternity test.

Step 5

Look at the paternity index (PI) of each genetic system to determine the odds of a match for that genetic system. The PI represents the probability that the man is the biological father in comparison to any other man in the general population.

Look at the combined paternity index (CPI) and probability percentage to determine the overall odds for the test. Multiply the paternity indices from each genetic system to determine the CPI. The lab converts the CPI to a percentage. For example, a percentage of 99.99 percent means that there is a likelihood to a degree of 99.99 percent that the tested man is the biological father of the child. A probability of zero means that the man is not the biological father.