Examining the relationship between inflammatory biomarkers during COVID‐19 hospitalization and subsequent long‐COVID symptoms: A longitudinal and retrospective study

INTRODUCTION: Long‐COVID is a heterogeneous condition with a litany of physical and neuropsychiatric presentations and its pathophysiology remains unclear. Little is known about the association between inflammatory biomarkers, such as interleukin‐6 (IL‐6) and C‐reactive protein (CRP) in the acute phase, and persistent symptoms after hospitalization in COVID‐19 patients. METHODS: IL‐6, CRP, troponin‐T, and ferritin were analyzed at admission for all patients with COVID‐19 between September 1, 2020 to January 10, 2021. Survivors were followed up 3‐months following hospital discharge and were asked to report persistent symptoms they experienced. Admission data were retrospectively collected. Independent t‐tests and Mann–Whitney U tests were performed. RESULTS: In a sample of 144 patients (62.5% male, mean Age 62 years [SD = 13.6]) followed up 3 months after hospital discharge, the commonest symptoms reported were fatigue (54.2%), breathlessness (52.8%), and sleep disturbance (37.5%). In this sample, admission levels of IL‐6, CRP and ferritin were elevated. However, those reporting myalgia, low mood, and anxiety at follow‐up had lower admission levels of IL‐6 (34.9 vs. 52.0 pg/mL, p = .043), CRP (83 vs. 105 mg/L, p = .048), and ferritin (357 vs. 568 ug/L, p = .01) respectively, compared with those who did not report these symptoms. Multivariate regression analysis showed that these associations were confounded by gender, as female patients had significantly lower levels of IL‐6 and ferritin on admission (29.5 vs. 56.1, p = .03 and 421.5 vs. 589, p = .001, respectively) and were more likely to report myalgia, low mood and anxiety, when compared to males. CONCLUSIONS: Our data demonstrate that female patients present more often with lower levels of inflammatory biomarkers on admission which are subsequently associated with long‐term post‐COVID symptoms, such as myalgia and anxiety, in those discharged from hospital with severe COVID‐19. Further research is needed into the role of serum biomarkers in post‐COVID prognostication.