While levels of both biomarkers were initially elevated in patients with severe COVID-19; GFAP levels subsequently declined and NfL levels continued to increase in subsequent follow up. Further, a direct correlation between rise in plasma NfL levels and disease severity was observed.
Patients with moderate disease (that is patients who were admitted to hospital but not in need of ventilator support) also had raised plasma GFAP levels.The authors indicate that these rises have been greater than those seen in pre COVID Intensive Care studies and suggest that COVID-19 is causing brain injury.
Serum NfL levels as a predictor of disease severity
A study from Verona, Italy by Mariotto et al., (2020) found that 57% of the patient group had increased levels of serum NfL compared with the control group. Only patients without antecedent comorbidities, which could independently alter NfL levels, were included in this study.
Also, increased NfL serum levels were significantly associated with longer and more severe disease with patients being more likely to be admitted to Intensive Care Units and to undergo orotracheal intubation (p<0.01). However, the study was unable to find any statistically relevant association between neurological symptoms and serum NfL levels.
In conclusion, the papers identify NfL and GFAP as potential biomarkers for neurological damage in COVID-19. While larger studies with long term follow up are required, both biomarkers could be very useful in proving the effectiveness of therapeutics in COVID-19 clinical trials.