DNA paternity tests are widely trusted to establish whether a man is the biological father of a child, but scientists have documented rare situations in which initial results can be misleading.
The tests are considered highly reliable when conducted correctly, with accredited laboratories reporting accuracy rates above 99.9 per cent. However, sample-handling mistakes, unusual genetic conditions and similarities between close relatives can complicate the findings.
Paternity testing works by comparing genetic markers inherited by a child from the mother and the alleged father. Laboratories examine these markers to determine whether the man’s genetic profile is consistent with biological fatherhood.
Problems may arise if samples are collected, labelled, transported or processed incorrectly. In such cases, a laboratory could analyse the DNA accurately but attribute the results to the wrong person because of a mix-up during handling.
Another challenge involves a rare genetic condition known as tetragametic chimerism, in which one person has two genetically distinct populations of cells. This can cause DNA obtained from different parts of the same person’s body to produce different genetic profiles.
A study published in the European Journal of Medical Genetics in August 2023 documented a case in which researchers initially excluded a man as the biological father of a child.
The first analysis compared a cheek-swab sample from the child with a blood sample from the alleged father. The results excluded paternity at six genetic markers.
However, further testing using the man’s semen and samples from other tissues produced a different outcome. Researchers found genetic evidence supporting his paternity and linked the discrepancy to chimerism.
A separate case published in 2018 also documented a man whose paternity was initially ruled out through repeated DNA tests. Further investigations eventually established that he was the child’s biological father after researchers examined his genetic condition.
Scientists have also examined the possibility of a close relative being incorrectly identified as a child’s father. This can happen when the alleged father is a brother of the biological father, since close relatives share substantial amounts of genetic material.
A 2013 study published in the Croatian Medical Journal used 10,000 computer-simulated families to investigate the risk of false paternity identification.
Researchers reported a simulated false-inclusion rate of approximately 19 per cent in a specific scenario involving 15 genetic markers, where a sibling was presented as the father and the mother’s DNA profile was unavailable.
The figure does not represent the general error rate of DNA paternity testing. Instead, it highlights how genetic similarities and missing information can affect particular cases.
Including the mother’s DNA profile and examining additional genetic markers can help laboratories distinguish between close relatives and establish paternity more reliably.
People who question their results are advised to contact the laboratory that conducted the test and request a review. Independent testing at an appropriately accredited facility may also help resolve disputed findings.
For tests intended for use in court, identity verification and a documented chain of custody are important because they establish who provided the samples and how they were handled.
James Mekenye, Programme Director at the Family Peace Association Kenya, has cautioned against making DNA testing compulsory for every child at birth, arguing that the practice could expose families to painful consequences.
In an interview with The Kenya Times, Mekenye said DNA testing should generally be considered when paternity is questioned or concerns are raised by a third party, rather than being conducted routinely.
He added that requests for DNA testing often arise from a lack of trust between couples.
Although rare genetic conditions and procedural mistakes can complicate results, the documented cases do not mean DNA tests are generally unreliable. Rather, they demonstrate why disputed findings may require further investigation and why unusual results should be reviewed before conclusions are drawn.