 Apart from acute kiddney injury AKI, critically ill patients with sepsis or trauma can also exhibit glomerular hyperfiltration 2-4. Glomerular hyperfiltration is not easily recognized, because the decrease in serum creatinine is a late manifestation and generally interpreted as normal renal function. Glomerular hyperfiltration may have clinical consequences, because it leads to augmented renal clearance of water soluble drugs. This is especially relevant for antibiotics, because augmented clearance can lead to underdosing and therapeutic failure 5-9. Patients with glomerular hyperfiltration are generally younger patients with less severe disease 3 and often exhibit a hyperdynamic circulation. The mechanism of glomerular hyperfiltration is poorly understood. High catecholamine release with increased renal blood flow could play a role. Direct measurement of renal blood flow is not available in daily clinical practice. 