TY - JOUR T1 - Clinician guide to COVID-19 diagnostics JF - Archives of disease in childhood - Education & practice edition JO - Arch Dis Child Educ Pract Ed DO - 10.1136/archdischild-2020-321272 SP - edpract-2020-321272 AU - Mildred A Iro AU - Helen Umpleby AU - Emanuela Pelosi Y1 - 2021/03/18 UR - http://ep.bmj.com/content/early/2021/03/18/archdischild-2020-321272.abstract N2 - The novel SARS-CoV-2 virus responsible for COVID-19 has resulted in a worldwide pandemic. To curtail the ongoing pandemic, emphasis has been placed on enhanced testing. Consequently, there has been an exponential rise in the number of diagnostic platforms that are available. This review gives an overview of the diagnostic methods for COVID-19, highlighting key considerations needed when interpreting the test results.The aims of SARS-CoV-2 testing are to (1) diagnose acute infection in symptomatic patients, (2) screen for and diagnose asymptomatic infection and (3) identify past infection. The detection assays used include nucleic acid amplification tests (NAATs), antigen-based tests and antibody (serological) tests.NAATs are aimed at identifying the presence of SARS-CoV-2 ribonucleic acid (RNA) in a sample. Reverse transcription polymerase chain reaction (RT-PCR) is the gold standard NAAT used for the diagnosis of COVID-19. In RT-PCR, repeated, automated cycles of heating and cooling (thermocycling) are used to amplify specific targets, that is, segments of the virus’ genome. The targets for SARS-CoV-2 include open reading frame 1ab/RdRp, envelope, nucleocapsid (N) and spike (S) genes (figure 1). The amount of virus in a sample is then quantified in real time using fluorescently labelled probes. A test is positive if the fluorescence goes above a certain threshold level. The number of thermocycles required to get over this threshold is termed the cycle threshold (Ct) value. The lower the Ct value, the higher the quantity of viral genetic material in the sample; this is used as a proxy for viral load and infectivity. A 3.3-point increase in Ct value is equivalent to a 10-fold decrease in the quantity of viral genetic material. Roughly speaking, a Ct value of <35 (across all targets) indicates active infection and strongly correlates with cultivable virus,1 whereas a Ct value of >35 is considered a low-level positive … ER -