Prognostic Value of Serum/Plasma Neurofilament Light Chain for COVID-19 Associated Mortality

Abstract

Given the continued spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), early predictors of coronavirus disease 19 (COVID-19) mortality might improve patients’ outcomes. Increased levels of circulating neurofilament light chain (NfL), a biomarker of neuro-axonal injury, have been observed in patients with severe COVID-19. We investigated whether NfL provides non-redundant clinical value to previously identified predictors of COVID-19 mortality. We measured serum or plasma NfL concentrations in a blinded fashion in 3 cohorts totaling 338 COVID-19 patients. In cohort 1, we found significantly elevated NfL levels only in critically ill COVID-19 patients compared to healthy controls. Longitudinal cohort 2 data showed that NfL is elevated late in the course of the disease, following two other prognostic markers of COVID-19: decrease in absolute lymphocyte count (ALC) and increase in lactate dehydrogenase (LDH). Significant correlations between LDH and ALC abnormalities and subsequent rise of NfL implicate multi-organ failure as a likely cause of neuronal injury at the later stages of COVID-19. Addition of NfL to age and gender in cohort 1 significantly improved the accuracy of mortality prediction and these improvements were validated in cohorts 2 and 3. In conclusion, although substantial increase in serum/plasma NfL reproducibly enhances COVID-19 mortality prediction, NfL has clinically meaningful prognostic value only close to death, which may be too late to alter medical management. When combined with other prognostic biomarkers, rising longitudinal NfL measurements triggered by LDH and ALC abnormalities would identify patients at risk of COVID-19 associated mortality who might still benefit from escalated care.

Figure 1:

Patient selection, objectives, and experiment outlines of 3 independent cohorts. Cohort 1 aims to analyze NfL cross-sectionally across disease diagnosis and severity categories. In cohort 2, objective was to analyze NfL levels in critically ill COVID-19 patients, longitudinally at 3 different time-points (T1, T2, and T3: collected averagely at 5 to 10 days interval, within 30 days of hospitalization). Observed additional prognostic value of NfL with traditional demographic factors (age and gender) from cohorts 1 and 2, was independently validated in cohort 3.

Figure 2:

In cohort 1, (A) NfL, (B) ALC, (C) CRP, and (D) LDH were compared across HC vs. COVID-19 disease severity and multiple sclerosis disease activity subgroups using Kruskal-Wallis ANOVA; **p < 0.005 and ****p < 0.0001. The dotted line on each plot indicates the median of HC.

Figure 3:

In cohort 2, (A) NfL levels at 3 different time points (T1, T2, and T3: collected on average at 5 to 10 day intervals, within 30 days of hospitalization) in critically ill COVID-19 patients were compared (survived versus died) using Kruskal-Wallis ANOVA; ****p < 0.0001. The dotted line indicates the median of the HC. (B) Longitudinal NfL levels in critical COVID-19 patients who died, plotted with respect to number of days before death. Each line represents data from an individual patient. The dotted line represents upper limit in HC (i.e., mean + 3*SD = 20 pg/ml). (C) Correlations between systemic biomarkers’ measurements at earlier time points (T1 and 2) and NfL measurements at later time points (T2 and T3) were assessed using linear regression analysis. R² and p-value are represented on respective correlation plots. The dotted line indicates 95% confidence interval.

Figure 4:

Comparisons of 3 predictive models of COVID-19 associated mortality: continuous NfL measurement, Age plus Gender, and Age plus Gender plus dichotomized NfL in 3 independent cohorts; (A) cohort 1, (B) cohort 2, and (C) cohort 3. The dotted line on each plot represents the optimal cut-off for respective model predictor. The numerical values beside respective subgroups (Survived or Died) on each plot represents the percentage of correctly classified patients.