Long-term effect of COVID-19 infection on kidney function among COVID-19 patients followed in post-COVID-19 recovery clinics in British Columbia, Canada

Background: We investigated the effect of Post-Acute COVID Syndrome or "long-COVID" on kidney function among patients followed in post-COVID recovery clinics (PCRC) in British Columbia, Canada.

Methods: Long-COVID patients referred to PCRC between July 2020 to April 2022, aged ≥18 years who had an estimated glomerular filtration rate (eGFR) value recorded at 3 months from the coronavirus disease 2019 (COVID-19) diagnosis (index) date were included. Those requiring renal replacement therapy prior to index date were excluded. Primary outcome was change in eGFR and urine albumin-creatinine ratio (UACR) after COVID-19 infection. The proportion of patients in each of the six eGFR categories (<30, 30-44, 45-59, 60-89, 90-120 and >120 mL/min/1.73 m2) and three UACR categories (<3, 3-30 and >30 mg/mmol) in all of the study time points were calculated. Linear mixed model was used to investigate change in eGFR over time.

Results: The study sample included 2212 long-COVID patients. Median age was 56 years, 51% were male. Half (∼47%-50%) of the study sample had normal eGFR (≥90 mL/min/1.73 m2) from COVID-19 diagnosis to 12 months post-COVID and <5% of patients had an eGFR <30 mL/min/1.73 m2. There was an estimated 2.96 mL/min/1.73 m2 decrease in eGFR within 1 year after COVID-19 infection that was equivalent to 3.39% reduction from the baseline. Decline in eGFR was highest in patients hospitalized for COVID-19 (6.72%) followed by diabetic patients (6.15%). More than 40% of patients were at risk of CKD.

Conclusions: People with long-COVID experienced a substantial decline in eGFR within 1 year from the infection date. The prevalence of proteinuria appeared to be high. Close monitoring of kidney function is prudent among patients with persistent COVID-19 symptoms.