Two Easily Available Lab Markers to Identify Patients at Risk of Severe COVID-19 [COVID-19 Updates]

This post will probably be most helpful to physicians or other front-line health care professionals who are treating COVID-19 patients and have the ability to order lab tests.

Please note that I myself am not a physician or a health care professional. I'm just bringing you the research.

Recent research suggests that two readily available lab tests can predict who is at risk of a severe and potentially fatal COVID-19 outcome with stunning accuracy.

The first is a research letter published in the Nature journal Signal Transduction and Targeted Therapy. They found that low lymphocyte percentage strongly predicts whether someone with a severe case recovers or dies. They focus on the lymphocyte count at two time points:

  • 10-12 days after symptoms arose, someone with a lymphocyte count below 20% would become a severe case and someone with a lymphocyte count above 20% would not.
  • On days 17-19 after symptoms arose, someone with a lymphocyte count below 5% would wind up in ICU and have a strong chance of dying within 12 days; someone with a count between 5-20%, by contrast, would recover.

However, if you look at Figure 1A, another point emerges: on the first day of symptoms, the mean lymphocyte count of people who never developed into a severe case was just over 25%, with very little variation. Those who wound up in ICU had a mean of 15%, with little variation. Those who wound up with severe cases that were cured also had a mean close to 15%, but (as represented by the error bar in the graph) there was a lot of variation in that group.

While the day one lymphocyte count cannot categorize people neatly like the days 10-12 count or the days 17-19 count, we can say that a day one lymphocyte count of 25% virtually guarantees someone will not wind up in critical care, while a day one count of 15% or lower means they will have a severe case and may become critically ill.

While this is only based on 70 patients and larger studies would be needed to confirm how well this holds up in large populations, it suggests that measuring the lymphocyte count on the first day of symptoms could be a very useful predictor of whether someone will need serious treatment and whether they have a chance of needing critical care, and that the days 10-12 and 17-19 counts can be used to categorize patients with greater accuracy.

The second study used 36 patients and was published on Saturday as a preprint, which means it hasn't yet been peer-reviewed. The vast majority of influential information circulating on COVID-19 comes from preprints simply because the situation is evolving so rapidly and it takes so long to get something peer-reviewed.

This study found that interleukin-6 (IL-6) is an extremely effective predictor of whether someone will require ventilation.

Typical levels of IL-6 in a healthy person are 5-7 pg/mL or lower.

Figure 1 from this paper shows how IL-6 can be used both at first admission to the hospital, and, when measured over time, at peak level, to predict who will need mechanical ventilation. Upon first admission, a threshold of 15 pg/mL or higher would capture everyone who would eventually need ventilation, while also including many patients who would not. A threshold of 50 pg/mL would eliminate 95% of those who would not need ventilation, while only losing 23% of those that would.

IL-6 is even more useful if measured regularly. 93% of those who would go on to need ventilation had a peak IL-6 above 80 pg/mL, while only 4% of those who did not need ventilation had a peak IL-6 that high.

Everyone who went on to need ventilation had a peak IL-6 above 50 pg/mL, while only 17% of those who did not need ventilation had a peak IL-6 that high.

This suggests that IL-6 at hospital admission could help triage patients by predicting their need for ventilation, and that serial IL-6 measurements could be used to track the change in that likelihood over time. Again, larger studies will be needed to confirm how well this marker holds up in large populations.

Taken together, initial and serial measurements of lymphocyte counts and IL-6 are likely to be very useful for triaging patients and predicting outcomes.

Stay safe,

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I am not a medical doctor and this is not medical advice. I have a PhD in Nutritional Sciences and my expertise is in conducting and interpreting research related to my field. Please consult your physician before doing anything for prevention or treatment of COVID-19, and please seek the help of a physician immediately if you believe you may have COVID-19.


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