CST3 and COVID-19: To further enhance the understanding of the renal impacts of COVID-19, particularly in severe cases, it is crucial to consider the differential clearance of creatinine and cystatin C. Creatinine, with a molecular weight of 0.11 kDa, and cystatin C, at 13 kDa, provide insights into changes in glomerular filtration barrier properties, potentially indicative of “shrunken pore syndrome” (SPS).