PCR - Polymerase Chain Reaction

Polymerase Chain Reaction is a technique to amplify small segments of DNA for molecular and genetic analysis. These amplified DNA can be used by laboratory procedures. The entire cycling process of PCR is automated and can be completed in just a few hours - guided by a temperature altering system known as thermocycler.

The polymerase chain reaction (PCR) test can measure the presence of viral nucleic acids in the patient’s blood even when there is no detectable antibody. Numerous copies of a gene are made by separating the 2 strands of DNA containing the gene segment, marking its location, using DNA polymerase to make multiple copies. PCR test is used to evaluate false negative results to the ELISA and Western blot tests.The PCR test can detect the presence or absence of antigens by determining whether cells have the genes for the antigens.

PCR test is becoming first choice of techniques for the detection of many bacteria/virus - from Anthrax to SARS-CoV-2. PCR technique is a major tool in the ongoing fight against the Covid-19 pandemic. It helped to positively match the specific coronavirus present in the lung tissue, blood and feces of infected animals to the exposure virus.
Even most mapping techniques in the Human Genome Project (HGP) relied on PCR.

Reverse Transcription Polymerase Chain Reaction (RT-PCR): Reverse Transcription Polymerase Chain Reaction is a method of polymerase chain reaction amplification of nucleic acid sequences that uses RNA as the template for transcribing the corresponding DNA using reverse transcriptase. It (RTPCR) relies on chemical analysis of the substance in the body that transmits genetic information (RNA) to:

• Evaluate the effectiveness of cancer therapies
  
• Identify mutations consistent with the presence of Ewing’s sarcoma
  
• Reveal cancer that recurs after treatment has been completed
  

HIV test in Infants

Babies born to mothers infected with HIV may or may not get infected with the virus. But the babies carry their mother's antibodies for HIV for several months. A doctor may find it very difficult to make definitive diagnosis of HIV infection in babies who lack symptoms until after 15 months of age. In recent times, PCR (polymerase chain reaction) assays or HIV culture techniques are employed to identify about one-third of infants who are truly HIV infected. With the current techniques, 90 percent of the HIV infected infants are identifiable by two months of age and 95 percent by three months of age. In fact PCR can detect minute quantities of the virus in an infant's blood.

Pre-test and Post-test counseling sessions are key to HIV testing. Counseling plays a very important role in getting a person to do HIV antibody test. Only a trained counselor can alleviate the fears in the individual and help prepare for getting test results. HIV infection often causes no symptoms in early stages. HIV antibodies also do not reach detectable levels in the blood for one to three months following the infection. Therefore people exposed to the virus should get an HIV test as soon as they are likely to develop antibodies to the virus within 6 weeks to 12 months after possible exposure to the virus.