Amber Shaw, of IDENTIGENE’s customer service answer’s this weeks Ask Kate question.
Inconclusive paternity test results generated by most laboratories typically means that the probability of paternity was < 99%. This is most likely caused by a number of differences between child and the alleged father at one or more genetic markers (loci) or the alleles (genetic variations) shared between child and the alleged father were so common that the collective strength of all the markers did not add enough statistical strength to the calculation to give a definitive “not excluded” result.
Differences between child and the alleged father could be caused by true generational mutations which occur naturally and randomly thru generations. Because the mutations are taken into consideration in the paternity calculations, the probability suffers because the dissimilarities between child and alleged father must be accounted for.
The results calculation is based upon the individual relationship indices (RI). The RI indicates how common, or how rare, each marker is at each locus according to population. If you have one (or more) rare markers that are passed to the child, that index number will increase the combined paternity index (CPI). An inclusive result is a combined parentage index of 99% or higher.
IDENTIGENE releases definitive results based upon two things:
- Inclusions: Probability of paternity of 99% or higher.
- Exclusions: 3 or more exclusionary markers (alleles do not match between child and the alleged father).
Many laboratories release an exclusion result requiring only 2 exclusionary markers be present. Our minimum is a more conservative number of 3 exclusionary markers. Although it is less likely to have 2 differences between a child and true biological father, it is still possible and based upon what is seen in the laboratory, implies there needs to be more investigation because a close relative of the alleged father (such as the father or brother of the alleged father) could potentially be the father . IDENTIGENE releases a result of inconclusive when there are 2 differences between child and an alleged father for two reasons:
- Because exclusionary results are definitive, we take a more cautious and conservative approach to ensure the result is as accurate as possible.
- Typically when two differences exist between child and the alleged father, the brother of the alleged father is a potential candidate for being the true biological father. This is based upon experience on what is actually seen in the laboratory and deserves closer examination.
Read here for more information on understanding the Paternity Index: http://www.dnatesting.com/dna-testing/paternity-index.php

