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Relation between Ct values in RT-PCR and clinical presentation of COVID-19 patients
Relation between Ct values in RT-PCR and clinical presentation of COVID-19 patients
Luis E. Fernández-Garza 1 
, Hugo A. Barrera-Saldaña 2
1 Departamento de Medicina Interna, Hospital General de Zona con Medicina Familia No. 2, Instituto Mexicano del Seguro Social, Monterrey, Nuevo León, México; 2 Vitagénesis S.A. e Innbiogem S.C., Laboratorio Nacional de Servicios Especializados de Investigación, Desarrollo e Innovación (LANSEIDI) para Fármacos Químicos y Biotecnológicos, Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI). Monterrey, Nuevo León, México
*Correspondence: Hugo A. Barrera-Saldaña. Email: hbarrera@columbia.com
Abstract
Background: The utility of reporting cycle threshold (Ct) values in COVID-19 testing remains debatable. Objective: To investigate the relationship between viral load and the clinical presentation of COVID-19. Material and methods: An observational retrospective study of COVID-19 patients whose samples were processed with a kit targeting the N and E genes. A Ct value < 40 was considered positive. Results: 657 resulted positive, with a mean age of 36 years and a male predominance (72.6%). 60.1% presented with symptoms, the most prevalent were headache (68.6%), cough (58%), myalgia (45.6%), and fever (44.3%). Asymptomatic patients had higher Ct values for both genes than symptomatic patients. In symptomatic patients, Ct values for the N gene were lower in those with headache, cough, and fever, but higher in those with anosmia/ageusia. Similar patterns were observed with the E gene. Conclusions: Elevated Ct values were associated with asymptomatic patients, whereas low values (high viral loads) correlated with the presence of fever. These data suggest that routine reporting of Ct values may serve as a useful indicator of initial clinical severity.
Keywords: Ct values. COVID-19 symptoms. Viral load. SARS-CoV-2.
