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Tuesday, September 27, 2022

Can a PCR Test Be False Positive?

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There is widespread concern about the potential for mistakes in diagnosis during the ongoing COVID-19 epidemic, with PCR and the more rapid antibody-based tests both being under review. Understanding the nature of various sorts of errors is necessary for estimating the potential severity of these mistakes during a pandemic. 

The reliability of a newly developed and implemented test, such as the one being used to detect the present coronavirus, cannot be determined with absolute certainty in advance. The high number of random variables in the actual world might increase the error rate of a test that was produced under ideal laboratory settings. 

PCR amplification processes are very selective for the target sequence. In other words, you can’t amplify something that doesn’t exist. While it’s true that a minimal amount of virus can be discovered, this in no way indicates that the virus isn’t there or that you aren’t infectious.  

You could think the initial test was a false positive if you retook it and got a negative result since you didn’t have any viral nucleic acids in the sample this time around. Accuracy of a PCR test is determined by two factors: sensitivity, or the proportion of infected persons that are detected, or the percentage of healthy people who are ruled out. 

According to this evaluation, the sensitivity of many PCR tests is 100%. The FDA suggests comparing the findings of the proposed test to an existing high-sensitivity PCR test by evaluating 30 positive clinical samples and 30 individual negative samples. 

Can a PCR Test Be False Positive?

Yes, from cross-contamination! Although PCR testing is the most effective method currently available for identifying COVID-19, four common circumstances are experienced in procedure:  

  • A true positive test result for COVID 
  • A false positive result: When someone who does not have COVID receives a positive result from a test. 
  • A negative test result: When a patient who really has the virus are a false negative. 
  • A true negative result: When someone really do not have a COVID and tests a true negative result. 

First and fourth are the ideal outcomes of the testing process, whereas the second and third are examples of mistakes. There is evidence to suggest that computer-generated readouts can be inaccurate; nevertheless, the addition of human judgment can correct cycle threshold-based positive misinterpretations. 

According to Layfield, further errors include the possibility of sample well cross-contamination within the analyzer (a positive sample might flow over into a negative sample, for example) or the insertion of the incorrect sample into the incorrect well. 

Vice head of microbiology committee and Cleveland Clinic attending physician Daniel Rhoads, MD, has said that when using PCR, it’s not uncommon to get a false negative result and the sensitivity of PCR for identifying COVID-19 is really approximately 80%. Therefore, it is estimated that 20% of people with COVID will test negative. 


According to the results of this systematic review, up to 58% of COVID-19 patients may have initial false-negative PCR results, highlighting the need to implement a correct diagnostic strategy and lessening the disease burden. To reduce the false-negative result, US Travel and COVID Testing Lab are delivering the best PCR test in Huntsville. 

The studies illustrate that modest quantities of viral RNA in the late stages of illness, after infection has disappeared, can contribute to false-negative results, together with observer error. Clinicians need to be aware that COVID-19 patients in the latter stages of infection may have negative PCR test findings.  

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