Renal Resistive Index (RRI) is a measurement of the resistance of the renal blood flow. A value higher than 0.70 is a marker of increased resistance and is correlated with kidney injury and its severity. Additionally, it may be associated with the mortality rate in the post‐surgery population. In COVID‐19 subjects, we found that high RRI has been associated with high levels of serum C‐reactive protein, a marker of systemic inflammatory reaction syndrome. Finally, we propose RRI not only as a marker of kidney injury, but also as a tool to evaluate the course of critical illness.