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Ct value may predict the severity and outcome of Covid-19

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Dr Veena Aggarwal, Consultant Womens’ Health, CMD and Editor-in-Chief, IJCP Group & Medtalks Trustee, Dr KK’s Heart Care Foundation of India    29 September 2021

Baseline cycle threshold (Ct) value may be a useful prognostic indicator for hospitalized Covid patients, suggests a new study published in the journal PLoS One.

The retrospective study included 461 patients who had been hospitalized with acute Covid-19 within four days of development of symptoms and positive RT PCR test for SARS-CoV-2 using a nasopharyngeal sample. The participants were recruited between 4th April and 5th June, 2020. The baseline cycle threshold (Ct) values were also determined.

Results showed that the prognosis in all those patients who had a high viral load at baseline was poor. They were more likely to need oxygen supplementation via nasal cannula, non-rebreather mask, or high-flow nasal cannula. The probability of intubation and mechanical ventilation was also higher in these patients. They were also likely to require hemodynamic support. The duration from symptom onset to PCR testing was 3 days in patients with high and intermediate initial viral loads, while this duration was 5 days in patients who had a low initial viral load. The inflammatory markers - lactate dehydrogenase (LDH), C-reactive protein (CRP) and ferritin - were likely to be higher at baseline in patients with a high initial viral load. However, no between-group differences were observed in the levels of troponin or chest X-ray findings. Patients who had an initial intermediate viral load had greater risk of mortality during their hospital stay, but were not likely to need intubation.

The number of new cases with a high initial viral load over time declined with mortality also decreasing during the study corresponding to the reducing severity of the pandemic. The number of samples with high and intermediate viral loads gradually declined and an increase in the number of positive samples with low viral load was noted. By the end of the study, the majority of the specimens showed low viral load.

This study has demonstrated an association of the initial viral load, as estimated by the Ct value, with the risk for intubation and in-hospital mortality. Hence, the baseline Ct value may help to identify patients who are likely to have adverse prognosis. In addition, the study authors suggest that Ct values may also help predict the course of the pandemic when evaluated at a population level. 

Reference

  1. El Zein S, et al. SARS-CoV-2 infection: Initial viral load (iVL) predicts severity of illness/outcome, and declining trend of iVL in hospitalized patients corresponds with slowing of the pandemic. PLoS One. 2021 Sep 16;16(9):e0255981. doi: 10.1371/journal.pone.0255981.

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