Control samples in lab results
Control samples are known substances used in laboratory analyses to ensure the accuracy and reliability of test results. They are essential for quality control, helping to identify and eliminate inaccuracies that could lead to false positives or false negatives in test outcomes. Control samples, also referred to as controls or known samples, facilitate the verification of laboratory results across different facilities, ensuring consistency and reliability in scientific findings.
In forensic laboratories, various control samples are utilized to confirm the presence of specific substances, such as known drugs or DNA profiles, which are critical for legal proceedings. Reliable sources, like the Forensic Science Service in England, provide these known samples to maintain high-quality standards. Additionally, blank control samples, which are known to contain no target substance, are used to monitor potential contamination in testing processes. If inconsistencies arise between control samples and test results, it signals a need to investigate and rectify potential issues in the laboratory's quality control measures. Understanding the role of control samples is vital for comprehending how laboratories ensure the credibility of their findings in various fields, including forensic science and medical testing.
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Control samples in lab results
DEFINITION: Samples of known substances used to ensure that laboratory analyses produce reliable results.
SIGNIFICANCE: Quality control is an important part of eliminating inaccuracy in laboratory results. Control samples ensure that laboratory results are reliable and can be duplicated in other laboratories following the same quality-control standards.
Control samples (also called controls, known samples, or knowns) provide a level of quality control that can verify laboratory test results. When a control sample is not used, it is possible for a laboratory result to be a false positive (a result that indicates something is true when, in fact, it is false) or a false negative (a result that indicates something is false when, in fact, it is true).
Forensic laboratories may use a variety of control samples to ensure accurate results. For example, they may use known combustibles to verify that particular combustibles are present in cases and known drug samples to verify that particular drugs are present in drug cases. Known (deoxyribonucleic acid) samples are used to compare with unknown DNA samples (for example, in the comparison of a suspect’s DNA with DNA found at a crime scene).
In many cases, forensic laboratories acquire the known samples they use as controls from reliable outside sources. For example, the F Service (FSS) in England, an internationally recognized leader in applied forensic technology, is a widely respected source of reliable control samples for fibers and paints. Crime labs around the world use control samples from such sources to ensure that they are meeting the quality standards necessary for their results to be accepted in courts of law.
Another type of control sample is a blank, or a control sample that is known to contain nothing. In this type of control, the sample is known to not contain the substance for which an investigator is testing. For example, if a known blank and a substance suspected of being an illegal drug are tested, and both tests produce positive results, indicating the presence of the drug, something is wrong with the quality control in the laboratory. It is possible that the equipment is contaminated by previous drug testing and needs to be sterilized, that there is some problem with the questioned sample, or that the control sample has been contaminated in some way.
Bibliography
Best Practices for Specimen Collection and Preservation for Forensic Toxicology. American Academy of Forensic Sciences, 2023.
Evans, Colin.The Casebook of Forensic Detection: How Science Solved One Hundred of the World’s Most Baffling Crimes. Updated ed. New York: Berkley Books, 2007.
Fisher, Barry A. J. Techniques of Crime Scene Investigation. 7th ed. Boca Raton, Fla.: CRC Press, 2004.
Genge, N. E. The Forensic Casebook: The Science of Crime Scene Investigation. New York: Ballantine, 2002.
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 4th ed. Boca Raton, Fla.: CRC Press, 2014.