Gleeson PJ, et al. - In this prospective observational study performed in a mixed medical-surgical intensive care unit (ICU) in Europe, researchers characterized renin in critically ill patients and determined its performance as a marker of tissue-perfusion. They also assessed if its use in critical care practice could be confounded by diurnal variation, continuous renal replacement therapy, and drug-interference. Participants included adults with a baseline estimated glomerular filtration rate >30 mL/min/1.73 m² and anticipated ICU stay > 24 hours. They obtained 112 arterial samples from 20 patients with septic shock (30%), hemorrhagic shock (15%), cardiogenic shock (20%), or no circulatory shock (35%). The ICU mortality rate was 30%. Findings revealed that diurnal variation, continuous renal replacement therapy, or drugs had no significant impact on renin measurement. They also found that renin served as a marker of tissue-perfusion and performed better than lactate as a predictor of ICU mortality.