• "The laboratory you select must be accredited by the American Association of Blood Banks(AABB)... Under no circumstances should a third party be involved in the process of selecting a lab, scheduling the appointment, or any other process outlined in the next steps."

    U.S. Department of State
  • "Please be aware that many non-accredited businesses advertise on the Internet as being AABB-accredited. It is important to note that these "resellers" - who are not AABB-accredited - will claim to use an accredited lab for their testing. For the purpose of this request, samples collected from and comparative tests arranged through "resellers" will not be accepted. "

    USCIS - California Service Center
  • "The test must be performed directly through an AABB-accredited facility. Please visit the AABB website (ww.aabb.org) to find an accredited lab, which will also coordinate the testing of the claimed relative - if they reside overseas. Please be aware that many non-accredited businesses advertise on the Internet as being AABB-accredited. "

    USCIS - California Service Center
Home - DNA Test for Immigration - Reading DNA Test Results
Reading DNA Test Results

DNA family relationship testing involves the analysis of the genetic information inherited by a child from his parents. The genetic information analyzed is contained within DNA located in virtually all cells of the body. The DNA used for biological relationship testing is usually obtained from cheek cells or from the white cells in a blood sample taken from the tested parties. The DNA obtained from different sample sources is exactly the same.

In a relationship DNA test, genetic markers, passed from parents to child, are tested and analyzed. A child inherits half of his DNA from the mother and the other half from the father. This means that on any given genetic marker containing one pair of alleles, one allele comes directly from the mother and the other one from the father. No two persons share the same DNA except for identical twins.

DNA family relationship testing compares the genetic profiles of all tested parties, which are generated by examining the allele sizes of the selected genetic markers of each participant, and calculates the statistic odds of matches between these profiles.
The following are a few terms that are important in understanding a DNA relationship test report.


DNA stands for Deoxyribonucleic acid. It is a chemical substance found in cells of all living things. DNA, which is inherited from the biological parents, contains the code for our physical attributes as well as the instructions for all functions of the body, including growth, development, and replication. DNA is composed of four different chemical bases (A, T, C, and G) that function like letters in the code.

Genetic Marker/Locus (plural-“loci”)

A genetic marker or locus indicates the position of DNA on a chromosome. The word “loci” is often used to describe the genetic markers used for DNA testing. For example, D3S1358 the D marker is on the 1358th locus described on chromosome 3. The letters in the marker name provide other information about the DNA molecule where the marker is found.

The genetic markers analyzed in a relationship test conducted by an AABB-accredited DNA testing laboratory include at least the 13 core loci specified by FBI for human identification. The marker phenotypes (observable chemical traits of an organism) of each tested party are listed in numbers, which specify the allele sizes of each tested marker. The number chart shows the characteristics of the DNA profiles for all tested parties and is one basic part of a DNA test report.

Typically, there are two numbers describing the phenotypes on each marker or locus. When only one single number shows on a specific marker, the tested person has two copies of the same marker inherited from both parents, a situation also known as homologous. We all inherit one of these two numbers from the father and the other one from the mother.


An allele is one of many forms that a genetic marker may take. DNA markers may differ in size or in the arrangement of the molecules (A, T, C and G). These differences make each person’s DNA profile unique. The data in a DNA report typically shows two allele sizes as numbers at each locus for each person, one allele contributed by the person’s biological mother and the other allele contributed by the biological father. By convention, when the two alleles at a locus are the same, the number is shown only once.

Interpretation of DNA Test Results

Reading Paternity or Maternity DNA Test Results

A paternity or maternity test report lists the genetic profiles of each tested party, displaying the allele sizes of the different markers tested. It also lists the Relationship Index (RI) for each marker—a statistical measure of how powerful a match is at a particular locus, which signifies relatedness.

DNA Marker Child Alleged Father Relationship Index (RI)
14, 16
11, 16
29, 30
29, 31
10, 11
10, 12

The table below shows partial results of a paternity test. The allele sizes of a child and the alleged father’s markers are listed. The numbers in blue indicate markers that the child inherited from the father. The RI on marker D8S1179 shows that there is a 1 in 3.6232 chance that another random person could have passed on the same allele size to the tested child. This number is stronger than the other two probably because the other two are more commonly found in the population.

The RI’s for each marker are multiplied with each other to produce the Combined Paternity Index (CPI), which is the genetic odds that the tested man is more likely to be the biological father compared to an unrelated man of the same race using the FBI allele frequency database. The CPI is then converted into a Probability of Paternity value, which is the likelihood (expressed in percentage form) that the tested man is the father of the tested person based on a random probability of 50%.

As a guideline, it is generally accepted by most courts and government agencies that a CRI of 100 and a probability of 99% or higher is strong proof that the tested man is the biological father of the tested child. On the other end of the spectrum, the probability is always 0% when the tested man is excluded as the biological father of the tested child.

In some rare cases, a genetic mutation may cause unexpected testing results. When it is observed in a paternity or maternity test, the non-match can lower the Combined Paternity Index to below 100, and this could be misinterpreted resulting in a false conclusion of exclusion. In these cases, a quality AABB-accredited DNA testing laboratory will test more genetic markers to make sure that an alleged father will not be excluded if there is only one non-match detected. AABB also requires that all exclusion cases be retested to guarantee accuracy.

Reading Siblingship and other Kinship DNA Test Results

Other kinship tests are performed using the same methodology. Genetic profiles of all tested parties are compared to find matches on the selected genetic markers. Instead of using the Paternity Index (PI), other relationship index such as grandparentage index or siblingship index are used to calculate the genetic odds for the tested parties to be related.

However, with the same testing methodology, other kinship tests such as a siblingship DNA test can yield a wide range of probability of relatedness, which is caused by the smaller chance of inheriting the same DNA when the relationship is further apart. For example, two full siblings share 50% of their genetic material as opposed to 100% for a child-parents relationship.  Because of the four possible combinations of inherited alleles at a particular marker location, two full siblings could have completely different allele sizes on the same genetic marker, which lowers the ultimate CRI and probability calculated by multiplying the odds for all matches detected on the tested markers.

Since siblingship tests are often requested by the immigration agencies to prove the claimed relationship, it is worth discussing the complexity of siblingship DNA test results. Because siblingship tests are much more complicated and variable, there is no consensus definition for an acceptable threshold in the scientific community. In a landmark article published in Transfusion (AABB’s Scientific Journal) by Dr. Robert Allen, it is suggested that a CRI of 10% (probability of 90%) support the claim of full siblingship, a CRI of 50 (probability of 98%) strongly support the claim, and a CRI of 100 or greater (probability of 99% or higher) practically prove the relationship.