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Can a blood test produce the wrong results?

One question lawyers, scientists, and others who are involved in the legal system face is about the accuracy of various methods used to collect and analyze evidence. From DNA to blood tests, hair comparisons, and fingerprints, the various techniques used by police and forensic investigators are complex, and while they may be powerful, they are not error-free. No matter how well-refined these processes become, the fact is that no method of evidence collection and analysis can be infallible because there is always the possibility for human error in the process.

False positives and false negatives

The first thing to understand about any kind of scientific test is that there are times when you get inaccurate results, both positively and negatively. These are called false positives and false negatives, and there can be a variety of reasons why they happen, including:

  • Equipment is miscalibrated
  • Mistakes in the procedure
  • Unintentional contamination of samples
  • Skipped steps in the process
  • Mislabeled samples

In addition to those issues, various tests can have other reasons for false positives, such as the ability of certain diseases to leave chemical markers in the blood. Under most circumstances, when individuals seek medical testing for their own health and treatment of disease, the tests are run multiple times to confirm results, particularly if there is a positive result for something that might be serious.

When it comes to testing for evidentiary purposes, labs do not always have transparent processes that are easy to critique, but there are ways to discover whether blood test results are inaccurate, and experienced attorneys will be able to help you understand when and how you can fight results you believe to be inaccurate so they do not affect a pending case.

How common are false results in blood tests?

As tempting as it might be to believe that blood tests and other scientific measurements can be infallible, the fact is that false positives and false negatives can be quite common. There's no way to know for sure how common, but by looking at how often biotech companies and labs admit to mistakes, even systemic mistakes that can affect large numbers of people, it becomes clear that this is an issue that needs more investigation. While it can be argued that state labs are held to higher standards than commercial testing companies, the fact is that this is not consistent and true across all jurisdictions.


If you have been charged with a crime and you believe it is related to inaccurate blood test results, you need to talk to an attorney right away. A qualified criminal defense attorney can advise you about your rights.

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