![]() Better measurement in PCR tests can mean improved health care, not just in treating COVID-19 but in many other types of medical tests. Our goal is to empower medical providers to make the best-informed diagnoses for their patients. Our model can improve the PCR test process by giving patients and providers more information. ![]() Instead, researchers infer the number from fluorescence measurements using a mathematical model. The number of nucleic acids in a sample is not measured directly. This is crucial for measuring gene expression, which enables scientists to understand biological processes and identify biomarkers for early detection of cancer. For a given genetic sequence, the goal is not only to detect it, but also to calculate how much was in your sample. In health care diagnostics, the fluorescence-based PCR test is regularly used to extract important information from samples. In forensics and food safety analysis, PCR testing is used to detect specific sequences of molecules that contain genetic information, known as nucleic acids (such as human or bacterial). The PCR test became part of everyone’s vocabulary a few years ago, but the technique was widely used before the pandemic and for many applications outside of COVID-19. This would allow people to make more educated decisions about coming in contact with others if they might have COVID-19. The goal of our model is to determine the likelihood that one result out of hundreds or thousands would be inaccurate.Ĭlinically, a lab could implement our model by adding an asterisk to a test result, instead of simply positive or negative, to indicate a possible inconclusive result. Specifically, it can tell us how the measurements would change if a very large number of tests were performed. Our model quantifies uncertainty in measurements, while accounting for imperfect copying of DNA and linking fluorescence to DNA (the more DNA is copied, the more fluorescence increases). ![]() Here at NIST, we developed a new mathematical model to characterize the likelihood of a test result being incorrect. An asymptomatic person with a small viral load may unknowingly spread the virus to others, especially if their PCR test came up negative. That may be because your viral load was low at the time of the first test. If you have had COVID-19, you may have had a negative test result shortly after infection and tested positive later. (Thinking back to the copy machine analogy, a very small mark could get lost in lots of copies.) This may result in a need to take multiple tests or could result in an incorrect positive or negative result. In this case, small errors in transferring portions of your sample between test tubes and tiny imperfections in copying the DNA can lead to significantly different fluorescence measurements. While the PCR-based test is the gold standard for diagnosis of COVID-19, it can be less accurate when the amount of virus in a sample is very small. The measurement of the fluorescence at the end of the test indicates whether the PCR test is positive. If the copying is successful, you can see evidence of fluorescent dye. ![]() The PCR test keeps track of this copying process. If one of the papers is not perfect, it’s going to affect many of your later pages. Think of it like making copies of copies on a copier 40 times. The PCR test multiplies the virus’s genetic code 40 times, sometimes producing millions to billions of copies of the original genetic code.īut the copying process is not perfect. When you look at your sample, you can’t tell whether COVID is present, as the virus’s genetic code is too small to be seen by the naked eye. The most common version of the test is based on a powerful, and widely used, lab technique called the polymerase chain reaction (PCR). The development of the clinical COVID test is a triumph of molecular biology and applied genetics. But, have you ever wondered, after your sample goes off to a lab, exactly how they arrive at a positive or negative result? My colleagues and I are working to make these excellent tests even more informative in ways that could improve diagnosis of COVID and many other diseases.
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