What Are the Causes of Bad DNA Test Results?

As the number of medical tests involving DNA analysis has grown, the accuracy of these tests has taken on an increased role in decisions people make about their lives and health. Specialists use DNA tests to confirm a diagnosis for some diseases, diagnose others before patients even show symptoms and predict risk factors for others, including some cancers. Prospective parents can learn whether they carry harmful genes that could be passed down to their future children, and women can have their babies screened for genetic diseases before they are born. It is even possible to predict a patient's response to certain prescriptions using DNA sequencing tests.



While useful on all these fronts, DNA testing is complex, and laboratories vary in their track records for accurate results. A number of factors can contribute to bad DNA test results.

Contamination

• DNA samples can become contaminated at any time before or during analysis, even before they arrive at the lab. Possible contaminants include DNA from other people, from other samples or from microbes. Other biochemical compounds can remain in samples when they are not purified well, or leftover chemicals can contaminate reactants not properly prepared. These impurities can weaken the analytical reactions or degrade the DNA in the samples. In prenatal testing, the mother's DNA sometimes contaminates samples.

Degradation

• Besides contaminants, other factors in the mishandling of samples can degrade, or break down, DNA. If a technician allows a sample to get too warm or stores it in a badly prepared chemical solution, the structure of the DNA can change. Thawing and refreezing the sample a number of times can cause it to break into pieces, making it impossible to determine its genetic sequence correctly.

Misidentified Samples

• Sometimes either the lab or the health care provider requesting the test simply switches one patient's sample with another patient's, and the individuals affected receive each other's results.

Misinterpreted Data

• The end result of a DNA test is a visual presentation of data that a prson must be interpreted by a person, or partly interpreted by a person and partly by a computer program. Some lab employees are more experienced in this or better trained than others, so human error does occur. The computer software can occasionally process data incorrectly.

Clerical Errors

• Clerical mistakes can occur before or after a techniciant runs the analytical test. Health care providers sometimes make errors or leave important information out in the referring paperwork or instructions. This can influence either the way the test is run or the interpretation of the results. The results report from the lab can contain transcription mistakes that misrepresent the real results.

Other Factors

• Bad test results can also occur in a number of other ways. The equipment used to run the tests can malfunction, especially if it is older. Technicians sometimes fail to follow the exact protocols they are supposed to or fail to keep quality control procedures in place. Some labs have misunderstood instructions and analyzed the wrong genes.