What are PCR tests?

PCR (polymerase chain reaction) is a fast and highly accurate way to diagnose certain infectious diseases and genetic changes. Tests example work by detecting the DNA or RNA of a pathogen (disease-causing organism) or abnormal cells in a sample in a lab.

• DNA is genetic material that contains instructions and information for all living things.

• RNA is another type of genetic material. It contains information copied from DNA and involved in making proteins.

Most viruses and other pathogens contain DNA or RNA.

Unlike many other tests, PCR diagnostic tests develop signs of disease in the earliest stages of infection. Other test results may miss early signs of illness because there are not enough viruses, bacteria, or other pathogens in the sample, or your body has not had enough time to generate an antibody response. Antibodies (rapid lateral flow test) are proteins made by your immune system to attack foreign substances such as viruses and bacteria. PCR tests can detect disease when there are very few pathogens in your body.

During a PCR test, a small amount of genetic material in a sample is copied several times in a laboratory. The copying process is known as amplification. If pathogens are present in the sample, amplification will make them much easier to see.

How are they used?

PCR tests are used to:

• for the diagnosis of certain infectious diseases

• to determine the genetic changes that can cause the disease

• to find a small number of cancer cells that can be missed with other types of tests.

How do service work?

PCR tests work:

• Taking a sample of blood, saliva, mucus, or tissue

• The sample will contain your own DNA and possibly the DNA of a pathogen or cancer cell.

• The sample is placed in a special machine. An enzyme called polymerase is added to the sample. This forces the sample to make copies.

• The copying process is repeated several times. In about an hour, billions of copies are created. If a virus or pathogen is present, it will be indicated on the machine.

Some viruses, including COVID-19, are made up of RNA, not DNA. For these viruses, RNA must be converted to DNA before copying. This process is called reverse transcription PCR (rtPCR).

PCR and rtPCR check for the pathogen. Another type of PCR known as quantitative PCR (qPCR) measures the number of pathogens in a sample, qPCR can be done concurrently with PCR or rtPCR.

What happens during a PCR test?

There are different ways to obtain a sample for a PCR test. Common methods include blood tests and nasal swabs. During a blood test, a healthcare professional will take a blood sample from a vein in your arm using a small needle. After the needle is inserted, a small amount of blood will be collected in a test tube or vial. You may feel a slight tingling sensation when the needle enters or exits. This usually takes less than five minutes.

A nasal swab can be taken from the front of the nostrils (anterior nasal passages). It can also be taken from the back of the nostrils in a procedure known as a nasal middle turbinate (NMT) swab, or from the nasopharynx, upper nose, and throat.

The COVID-19 RT-PCR Test is also designed to qualitatively detect SARS-CoV-2 nucleic acid in pooled samples using a matrix pooling strategy (i.e., Pooling Strategies) containing up to five separate upper respiratory tract swabs. (swabs from the nasopharynx, middle turbinate, anterior nose or oropharynx collected using separate vials containing the transport medium) per pool and 25 samples per matrix. Anterior nasal swab samples are collected in separate vials containing the transport medium, either under the supervision of a healthcare professional or independently using a home collection pcr test kit(home test kit) approved for use in this test.

A negative pooled test result should not be considered conclusive. If the patient’s clinical signs and symptoms are not consistent with a negative result, or if the results are necessary for patient management, then the patient should be considered for individual testing. Samples included in pools where a positive sample cannot be identified by the matrix should be individually tested before reporting the result. Low viral load samples may not be detected in sample pools due to the reduced sensitivity of pooled testing.

Results are intended to identify SARS-CoV-2 RNA. SARS-CoV-2 RNA is usually found in respiratory specimens during the acute phase of infection. Positive results indicate the presence of SARS-CoV-2 RNA; Clinical correlation with patient history and other diagnostic information is required to determine infection status. Positive results do not rule out bacterial infection or coinfection with other viruses. The detected agent cannot be a definite cause of the disease.

Negative results do not preclude infection with SARS-CoV-2 and should not be used as the sole basis for management decisions. Negative results should be combined with clinical observations, medical history and epidemiological information.

The COVID-19 PCR test is a real-time reverse transcription polymerase chain reaction (rRT-PCR) test. The test can be run in singleplex format (three separate assays for each of the three SARS-CoV-2 targets) or combined into one reaction (containing all 3 SARS-CoV-2 targets) and set up the amplification. In a single-plex format, the test uses three sets of primers and probes to detect three regions in the SARS-CoV-2 nucleocapsid (N) gene and one set of primers and probes to detect human RNase P (RP) in a clinical specimen.

When combined into a single reaction, the test uses two sets of primers and probes to detect two regions in the SARS-CoV-2 N gene and one set of primers and probes to detect RP. RNA isolated from upper and lower airway samples (e.g., nasal, nasopharyngeal or oropharyngeal swabs, sputum, lower airway aspirates, bronchoalveolar lavage, and nasopharyngeal lavage / aspirate or nasal aspirate) is back-transcribed into Flex7 cDNA and then amplified from Applied Biosystems (QS7) instrument with software version 1.3

During the amplification process, the probe is annealed with a specific target sequence located between the forward and reverse primers. During the extension phase of the PCR cycle, the 5′-nuclease activity of Taq polymerase disrupts the bound probe, causing the reporter dye to separate from the quencher dye, generating a fluorescent signal. The fluorescence intensity is monitored in each PCR cycle using QS7.

When checking the front nostrils, you will start by tilting your head back. Then you or the provider:

• Gently insert the swab into the nostril.

• Rotate the swab and leave it on for 10-15 seconds.

• Remove the swab and insert it into the other nostril.

• Take a swab from the second nostril using the same technique.

During your NMT swab, you will begin by tilting your head back. Then you or your ISP:

• Gently insert the swab into the lower part of the nostril, pushing down on it until you feel it stop.

• Rotate the swab for 15 seconds.

• Remove the swab and insert it into the other nostril.

• Take a swab from the second nostril using the same technique.

Are there risks to a PCR test?

The risk of getting a blood test is very low. You may have mild pain or bruising where the needle was inserted, but most symptoms go away quickly.

A nasal swab can tickle your throat or make you cough. A nasopharyngeal swab can be uncomfortable and cause coughing or vomiting. All of these effects are temporary.

What else do I need to know about PCR tests?

PCR tests are considered the best and most effective method for detecting many infectious diseases, including COVID-19 and Ebola. And because they can often make a diagnosis before symptoms of infection appear, PCR tests play a critical role in preventing the spread of disease.