Fluctuating RT-PCR Ct Values- A Case Series

Abstract

Real-time reverse transcriptase polymerase chain reaction (r RT-PCR) has been the main diagnostic tool for SARS-CoV-2 infection since the early stages of the COVID-19 pandemic and a positive test enables the clinicians and public health professionals to quickly isolate the patient and prevent spread of the disease. The presence of viral RNA confirms SARS CoV-2 and the Cycle threshold (Ct) values may give a rough estimate of viral load. Theoretically, the Ct value is inversely proportional to the amount of genetic material (RNA) in the starting sample and lower Ct values is generally associated with high viral load. Some experts assume that high viral load is directly correlated with increased infectiousness and severity of disease and suggest using Ct value or calculating viral load in decision-making. As per the policy, dated 14th June 2020, National Health Strategic Command Group in Qatar recommends using RT-PCR Ct value as a key determinant for decision on admission, discharge and isolation. The objective of this case series is to show that Ct values vary as the course of infection progresses, hence cannot be used as a reliable marker to take clinical decisions or even public health actions such as quarantine/ isolation. All six confirmed COVID-19 cases showed fluctuating RT-PCR Ct values throughout the course of illness. The Ct value was higher in the beginning of the course of infection, depicting low viral load and later in the course the Ct value dropped indicating higher viral load. The Ct value decreased as symptoms developed or worsened. There is a high probability that patients in early symptomatic stage may show a high Ct value which may subsequently change and thus management will change. In such cases, the high Ct values will give a false sense of security and thus have an impact on the containment of spread of infection to others. Hence, it is not recommended to rely on numerical Ct values for determining infectiousness of COVID-19 patients and deciding patient management protocols since the Ct value an indirect marker of viral load, changes over the course of infection.