COVID-19 viral load could help physicians predict illness severity

COVID-19 viral loads could be a useful indicator of which patients may need higher levels of care, The New York Times reports. 

A sizable body of research articles show those with higher viral loads are more likely to deteriorate and more likely to die compared to those with lower viral loads.

Viral load data is included in results from polymerase chain reaction tests, which are performed in cycles that double the viral genetic material from patients' samples. A low cycle threshold, or Ct, indicates a high viral load in the patient, meaning not many cycles had to be completed to yield a positive result, while a high Ct indicates a low viral load. 

The Times cited a study at New York City-based Weill Cornell Medicine in which researchers found 40 percent of patients with high viral loads, meaning their tests were positive at a Ct of 25 or below, died while in the hospital compared to 15 percent of patients with positive tests at higher Cts and lower viral loads. 

Since viral loads vary throughout the course of illness, some experts are wary of making assessments based on Ct values. The thresholds for a positive result also vary slightly depending on a machine's manufacturer. Others believe the benefits outweigh the concerns. 

"It doesn't change the fact that on average, when you look at the admission test results of these Ct values, they really identify patients at high risk of decompensating and dying," Michael Satlin, MD, lead of the Weill Cornell study, told the Times. 

Earlier this month, Florida mandated clinical labs to start reporting viral load data, according to the Times. The FDA also recently recommended that labs start reporting this information. 


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