Available data make it highly unlikely that all critically ill patients are depleted in glutamine, as only approximately one third of patients admitted to the ICU have a plasma glutamine concentration < 420 μmol/l. Furthermore, a higher risk of an unfavorable outcome indicated by a high APACHE II score or a high sequential organ failure assessment (SOFA) score is not statistically associated with glutamine depletion. In contrast, glutamine depletion at admission is not associated with risk scoring [4], [5]. However, the risk for a given patient may be increased if a low admission glutamine concentration is present (Figure 1). As pointed out by Rodas et al. this additional risk may be most pronounced for the group of patients with a moderate mortality risk [5]. If patient recruitment in a study focuses on patients with high mortality risk or low mortality risk, the additional risk associated with concomitant glutamine depletion will be less pronounced.