At what Covid-19 (Coronavirus disease 2019) cyclic threshold (Ct) value should treatment be initiated?

From the Guidelines

There is no specific cyclic threshold (Ct) value at which COVID-19 treatment should be initiated, and treatment decisions should be based on clinical symptoms, disease severity, risk factors, and time since symptom onset rather than PCR Ct values alone. While lower Ct values generally indicate higher viral loads, they don't reliably predict disease severity or treatment response 1. For outpatients with mild to moderate COVID-19 who are at high risk for progression, antiviral medications like nirmatrelvir/ritonavir (Paxlovid), remdesivir, or molnupiravir should be started within 5-7 days of symptom onset, regardless of Ct value.

Some key considerations for treatment include:

• The use of long-acting anti-SARS-CoV-2 monoclonal antibodies for pre-exposure prophylaxis in patients at high risk for severe COVID-19 1
• The recommendation for post-exposure prophylaxis with anti-SARS-CoV-2 monoclonal antibodies in patients at high risk for COVID-19 progression 1
• The use of dexamethasone during the inflammatory phase of the disease, particularly in patients with oxygen requirements and increased inflammatory markers 1

For hospitalized patients, treatment decisions including antivirals, immunomodulators like dexamethasone, or other interventions should be guided by clinical status and oxygen requirements. Ct values can vary between testing platforms and laboratories, making standardized treatment thresholds based on Ct values impractical. The focus should remain on prompt clinical assessment and timely initiation of appropriate therapy based on individual patient factors.

Key patient factors to consider include:

• Disease severity, with moderate COVID-19 defined as requiring oxygen support with saturation >90%, and severe COVID-19 defined as saturation <90% or respiratory rate >30/min 1
• Risk factors, such as age, underlying haematological malignancy, and immunosuppression 1
• Time since symptom onset, with antiviral treatment generally most effective when started within 5-7 days of symptom onset 1

From the Research

Covid-19 Cyclic Threshold Treatment

• The Covid-19 cyclic threshold (Ct) value is a measure of the amount of viral RNA present in a patient's sample, with lower values indicating higher viral loads 2.
• Treatment initiation based on Ct values is not explicitly stated in most studies, but it is suggested that patients with high viral loads (low Ct values) may benefit from antiviral treatment such as remdesivir 2.
• A study found that remdesivir decreased the risk of mortality and need for invasive mechanical ventilation in patients with high viral loads (Ct <25) and low-grade systemic inflammation 2.
• The following Ct value thresholds are associated with treatment outcomes:
  • Ct <25: associated with high viral loads and potential benefit from remdesivir treatment 2
  • Ct <25 and <5 day symptom duration: associated with reduced 28-day mortality with remdesivir treatment 2
• Other studies focus on treatment approaches based on clinical presentation, disease progression, and patient characteristics, rather than specific Ct value thresholds 3, 4, 5, 6.
• Treatment options for severe Covid-19 include antiviral drugs, immune-based agents, and anticoagulation therapy, as well as respiratory care such as high-flow nasal cannula therapy and non-invasive ventilation 6.