What is the Polymerase Chain Reaction (PCR) COVID-19 test?

From the Guidelines

The PCR COVID test is the gold standard for COVID-19 diagnosis, detecting the genetic material of the SARS-CoV-2 virus in a person's sample with high accuracy. This test is considered the most reliable method for confirming the diagnosis of COVID-19 due to its high specificity and moderate sensitivity 1. The test works by using specific primers that bind only to SARS-CoV-2 genetic sequences, allowing for targeted detection of the virus even when present in small amounts.

Key Points to Consider

• The PCR COVID test typically provides results within 6 to 8 hours, but can be as rapid as 45 minutes 1.
• A positive RT-PCR test for COVID-19 has more weight than a negative test because of the test’s high specificity but moderate sensitivity 1.
• False-negative results may be due to improper sampling, degradation of the viral RNA during shipping/storage, low viral loads, incorrect nucleic acid extraction, presence of amplification inhibitors, and mutation(s) in the RT-PCR target region 1.
• A single negative COVID-19 test should not be used as a rule-out in patients with strongly suggestive symptoms 1.

Clinical Implications

• The PCR COVID test is particularly useful for diagnosing current infections, even in asymptomatic individuals.
• The test's high sensitivity means it can detect the virus before symptoms appear and for several weeks after infection, though a positive result later in infection may not necessarily indicate contagiousness.
• Interpreting the result of a test for COVID-19 depends on two things: the accuracy of the test, and the pretest probability or estimated risk of disease before testing 1.

From the Research

Overview of PCR Covid Test

• The PCR Covid test, also known as real-time polymerase chain reaction (RT-PCR), is a diagnostic test used to detect the presence of SARS-CoV-2, the virus that causes COVID-19 2, 3, 4.
• The test works by amplifying the genetic material of the virus, allowing for the detection of even small amounts of the virus in a sample 3.

Types of Samples Used for PCR Covid Test

• The PCR Covid test can be performed on various types of samples, including:
  • Sputum samples, which have been shown to have the highest sensitivity 2
  • Nasopharyngeal samples, which have a lower sensitivity than sputum samples but are still effective 2
  • Saliva samples, which can be self-collected and have been shown to be effective in detecting the virus 2
  • Oropharyngeal samples, which have been shown to have the lowest sensitivity among the different types of samples 2

Sensitivity and Specificity of PCR Covid Test

• The sensitivity and specificity of the PCR Covid test can vary depending on the type of sample used and the primer sets used in the test 2.
• Studies have shown that the sensitivity of the PCR Covid test can range from 42.1% to 94.8%, while the specificity can range from 65.2% to 100% 2.
• The use of in-house-designed primer sets, such as the iNP RT-qPCR, has been shown to have better sensitivity and specificity than commercial primer sets 2.

Limitations and Challenges of PCR Covid Test

• The PCR Covid test is not without its limitations and challenges, including the potential for false-negative and false-positive results 3, 4.
• The test requires specialized equipment and trained personnel, which can limit its availability in some areas 3.
• The interpretation of the test results can be complex and requires careful consideration of the clinical context and other diagnostic information 4.