The Association among Cycle Threshold Value of RT-PCR, Viral Culture in Hospitalized COVID-19 Patients Receiving Corticosteroid Treatment


  • Panuwat Wongkulab Internal Medicine Department, Rajavithi Hospital, College of Medicine, Rangsit University
  • Wannakorn Homsuwan Research and Technology information, Rajavithi Hospital
  • Suchada Suphanpayak Biomolecular Laboratory, Department of Clinical Pathology and Medical Techology, Rajavithi Hospital
  • Chaicharn Deerochanwong Internal Medicine Department, Rajavithi Hospital


SARS-CoV-2shedding, Immunosuppressive drug, RT-PCR, Ct value, Isolation precaution


Background: During the COVID-19 pandemic era, the isolation period is a critical issue for bed management in hospitals. The cut-off time for isolation is controversy in COVID-19 patients receiving steroid treatment because the shedding time might be longer than patients who did not receive. The purpose of this study was to determine the infectivity period of SARS-CoV-2 by detecting cultivable virus. Objectives: The primary endpoint was the correlation between viral culture result and cycle threshold (Ct) value from the RT-PCR test. The secondary aim was the different of Ct values in each group. Methods: The cross-sectional study was conducted in Rajavithi Hospital, Bangkok, Thailand. We collected nasopharyngeal swabs (NPS) from COVID-19 infected patients, having symptoms at least 2 weeks, received steroid treatment as immunomodulator and performed virus culture during August to September 2021. We categorized patients into 3 groups by symptom duration. Results: Nasopharyngeal swabs (NPS) from 27 patients were eligible. 15 (55.6%) were female patients. The age was 64.7gif.latex?\pm15.7 year-old. Their symptom’s duration was 29.7gif.latex?\pm11.6 days. All patients received the dexamethasone or equivalent to 12.4gif.latex?\pm4.4 mg/day, with duration at 18.6gif.latex?\pm8.3 days. Also, 55.5% of patient received the methylprednisolone 404.2gif.latex?\pm154.3 mg/day, with 2.8gif.latex?\pm1.6 days. 23 (85%) patients had symptoms for over 20 days. All patients had SARS-CoV2- viral culture negatively. The value of Ct N gene (p = .27) and Ct ORF1ab gene (p = .17) were not difference among groups. IgM was detected in patients with symptom over 2 weeks. Conclusion: Our study showed the all patients had negative by viral culture. RT-PCR could be detected for more than 4 weeks and the Ct’s value were not difference. All patients had seroconversion since infection more than 2 weeks. Therefore, the duration of illness with seroconversion might be useful for stop isolation.


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How to Cite

Wongkulab P, Homsuwan W, Suphanpayak S, Deerochanwong C. The Association among Cycle Threshold Value of RT-PCR, Viral Culture in Hospitalized COVID-19 Patients Receiving Corticosteroid Treatment. J DMS [Internet]. 2023 Dec. 15 [cited 2024 Apr. 15];48(4):93-9. Available from:



Original Article