Monocyte Count Predicts Lung Disease Risk in COVID-19 Patients

University of Virginia (UVA) Health researchers have discovered a potential way to predict which patients with severe COVID-19 will likely recover well and which will likely develop long-haul lung problems. The findings, published recently in Frontiers in Immunology, could help clinicians better personalize treatments for individual patients.

UVA’s new research also alleviates concerns that severe COVID-19 could trigger relentless, ongoing lung scarring akin to the chronic lung disease, known as idiopathic pulmonary fibrosis (IPF), the researchers report. That type of continuing lung damage would mean that patients’ ability to breathe would continue to worsen over time.

“We are excited to find that people with long COVID have an immune system that is totally different from people who have lung scarring that doesn’t stop,” said researcher Catherine A. Bonham, MD, a pulmonary and critical care expert who serves as scientific director of UVA Health’s Interstitial Lung Disease Program. “This offers hope that even patients with the worst COVID do not have progressive scarring of the lung that leads to death.”

Investigating long COVID symptoms

Up to 30 percent of patients hospitalized with severe COVID-19 continue to suffer persistent symptoms months after recovering from the virus. Many of these patients develop lung scarring—some early on in their hospitalization, and others within six months of their initial illness, prior research has found. Bonham and collaborators wanted to understand better why this scarring occurs, determine if it is similar to progressive pulmonary fibrosis, and see if there is a way to identify patients at risk.

To do this, the researchers followed 16 UVA Health patients who had survived severe COVID-19. Some 14 had been hospitalized and placed on a ventilator. All continued to have trouble breathing and experienced fatigue and abnormal lung function at their first outpatient checkup.

After six months, the researchers found that the patients could be divided into two groups: One group’s lung health improved, prompting the researchers to label them “early resolvers,” while the other group, dubbed “late resolvers,” continued to combat lung problems and pulmonary fibrosis. 

Looking at blood samples taken before the patients’ recovery began to diverge, the UVA team found that the late resolvers had significantly fewer monocytes circulating in their blood. These white blood cells were abnormally low in patients who continued to combat lung problems compared both to those who recovered and healthy control subjects. 

Further, the decrease in monocytes correlated with the severity of the patients’ ongoing symptoms. This suggests that clinicians may be able to use a simple blood test to identify patients who may develop long COVID—and to improve their care.

Complete blood picture to the rescue

“About half of the patients we examined still had lingering, bothersome symptoms and abnormal tests after six months,” Bonham said. “We were able to detect differences in their blood from the first visit, with fewer blood monocytes mapping to lower lung function.”

The researchers also wanted to determine if severe COVID-19 could cause progressive lung scarring as in idiopathic pulmonary fibrosis. They found that the two conditions had very different effects on immune cells, suggesting that even when the symptoms were similar, the underlying causes were very different. 

This was true even in patients with the most persistent long COVID symptoms. “Idiopathic pulmonary fibrosis is progressive and kills patients within three to five years,” Bonham said. “It was a relief to see that all our COVID-19 patients, even those with long-haul symptoms, were not similar.”

Because of the small number of participants in UVA’s study, and because they were mostly male (for easier comparison with IPF, a disease that affects mostly men), the researchers say larger, multicenter studies are needed to bear out the findings. But they hope these findings will provide clinicians with a useful tool to identify COVID-19 patients at risk for long-haul lung problems and help guide them to recovery.

- This press release was originally published on the UVA Health website