Post-acute COVID-19 syndrome and kidney diseases: what do we know?

COVID-19, a disease caused by a novel coronavirus (SARS-CoV-2), is a major global threat that has turned into a pandemic. Despite the emergence of multiple vaccination alternatives and developing therapeutic options, dramatic short- and long-term clinical outcomes have been recorded with more than 250 million infected people and over 5 million deaths as of November 2021. COVID-19 presents various respiratory, cardiovascular, neuropsychiatric, musculoskeletal and kidney features during the acute phase; nevertheless, renal involvement in the post-infection period has recently been emphasized. The present review aims to evaluate the growing literature on kidney involvement in the SARS-CoV-2 infection along with clinical features reported both in the acute phase of the infection and in the post-acute COVID-19 period by assessing potential pathophysiological frameworks explaining such conditions. Chronic kidney disease and development of acute kidney injury (AKI) in the course of initial hospitalization are associated with high mortality and morbidity rates. Moreover, growing evidence suggests a decline in renal function in the 6-to-12-month follow-up period even in patients without any signs of AKI during the acute phase. Despite such concerns there are no guidelines regulating the follow-up period or therapeutic alternatives for such patient population. In conclusion, the burden of COVID-19 on the kidney is yet to be determined. Future prospective large scale studies are needed with long follow-up periods assessing kidney involvement via multiple parameters such as biopsy studies, urinalysis, measurement of serum creatinine and cystatin C, directly measured glomerular filtration rate, and assessment of tubular function via urinary β²-microglobulin measurements.