DNA testing is a widely used and generally reliable tool for confirming family relationships and aiding forensic investigations. While highly accurate, results can sometimes appear inaccurate or misleading. These instances stem from specific factors within the complex testing process, not fundamental scientific flaws.
Errors in Sample Handling
Errors can arise before a DNA sample even reaches the laboratory. Sample contamination, where foreign DNA mixes with the intended sample during collection or transport, is a common issue. This can lead to mixed DNA profiles, making accurate analysis challenging. Poor crime scene management or inadequate equipment sanitation can introduce external DNA.
Mislabeling or sample mix-ups, due to human error during collection or initial intake, are another potential error. If a sample is incorrectly attributed, analysis will not correspond to the correct person. This can result in a sample from one individual being analyzed and reported as if it belongs to another.
Improper storage or transport delays can degrade DNA, making it difficult to obtain a clear genetic profile. DNA degrades from exposure to moisture, temperature, and sunlight, hindering analysis. Low DNA quantity can also lead to inconclusive results.
Laboratory Processing Mistakes
Even when samples arrive at the laboratory in good condition, errors can occur during the complex analytical process. Reagent or equipment malfunctions are one source of potential inaccuracies; faulty chemicals or improperly calibrated machinery can lead to incorrect amplification, detection, or analysis of DNA markers. For instance, issues with the polymerase chain reaction (PCR) technique, used to amplify DNA, can result from slight mistakes or inappropriate conditions like temperature.
Human error by laboratory technicians can also compromise results through actions such as incorrect pipetting, improper dilutions, or procedural deviations. Cross-contamination within the lab, where DNA from one sample inadvertently transfers to another, is another concern that can lead to erroneous outcomes. Such errors can be difficult to detect during routine bench work.
The absence or failure of strict quality control protocols, such as positive and negative controls, can allow errors to go undetected. Quality control procedures are essential for maintaining reliability and ensuring that any technical issues or contamination are identified. Additionally, data entry errors, which occur when raw data is manually entered or transferred, can introduce inaccuracies into the final report, affecting the interpretation of results.
Challenges in Data Interpretation
Beyond direct errors in sample handling or laboratory processing, challenges in interpreting DNA data can lead to conclusions that seem “wrong” to a layperson. DNA matches are often expressed as statistical probabilities rather than absolute certainties, such as a 99.9% probability of paternity. Misinterpreting these statistics as 100% certainty can create misconceptions about the absoluteness of the result.
Complex genetic scenarios also present interpretive challenges. Spontaneous genetic mutations, though rare, can occur and might lead to a perceived mismatch that does not indicate non-parentage. Conditions like chimerism or mosaicism, where an individual possesses more than one distinct cell line or DNA profile, can further complicate test results.
DNA from close biological relatives, such as full siblings or identical twins, can be highly similar, making differentiation challenging. Identical twins, for example, cannot be distinguished by standard DNA tests. This can lead to unexpected matches or difficulties in establishing precise relationships, particularly in ancestry testing or in populations with a high degree of relatedness. The comprehensiveness and diversity of reference databases used in ancestry predictions or forensic matching also influence the accuracy and detail of results, as limitations in these databases can affect the ability to find a match or predict origins.
Verifying Questionable Results
If an individual suspects their DNA test results might be inaccurate, several actionable steps can be taken. A first step involves carefully reviewing the test report for any disclaimers, statistical explanations, or notes regarding sample quality or potential limitations. Understanding the specific metrics and language used in the report can provide important context.
Contacting the testing company or laboratory directly is also advisable to seek clarification on the results or inquire about their quality assurance processes. Reputable companies often have customer support or scientific teams available to address concerns and explain findings in detail. They may be able to re-examine the data or provide additional insights.
For critical results, such as those related to paternity or forensic cases, considering a second opinion or retest from a different accredited laboratory can offer independent verification. This can help confirm or refute the initial findings and provide greater confidence in the outcome. If the results are complex or unexpected, particularly in medical or ancestry contexts, seeking guidance from a genetic counselor can be beneficial. These professionals are trained to interpret complex genetic findings and explain their implications in an accessible manner.