Longitudinal assessment of glomerular and tubular kidney function after COVID-19: a prospective cohort study.

BACKGROUND: COVID-19 is a multi-organ disease affecting the kidneys, but the extent of persistent kidney injury and the utility of novel biomarkers remain unclear. We investigated patients with COVID-19 regarding initial impairment and recovery of glomerular and tubular function during 6 months. METHODS: We conducted a prospective cohort study comprising 77 hospitalized and 141 non-hospitalized patients with COVID-19 in Sweden. Plasma samples collected during the acute phase and at 3- and 6-month follow-up were analyzed for glomerular markers creatinine and cystatin C to estimate glomerular filtration rate (eGFR). Tubular markers included kidney injury molecule-1, osteoactivin, trefoil factor 3, and vascular endothelial growth factor-A. RESULTS: Hospitalized versus non-hospitalized patients demonstrated lower eGFRcystatin C across time-points, while eGFRcreatinine was less specific. Kidney injury molecule-1 and vascular endothelial growth factor-A were persistently higher in hospitalized patients. Osteoactivin was lower at the acute phase and higher at 3- and 6 months follow-up in hospitalized patients. Recovery from the acute phase to 6 months was observed in both groups, although the biomarker levels were consistently worse for hospitalized patients. CONCLUSION: Glomerular and tubular kidney functions remained more impaired in hospitalized COVID-19 patients compared to non-hospitalized for 6 months. We recommend eGFRcystatin C for evaluation of glomerular function during COVID-19. The tubular injury markers kidney injury molecule-1 and vascular endothelial growth factor-A were markedly elevated in hospitalized patients, consistent with more sustained interstitial inflammation. This finding suggests that these patients may require closer clinical monitoring.