For these reasons, in the clinical setting, it is often necessary to initiate or adjust antimicrobial therapy on an unsure ground and the relevant therapy may in some situations be delayed for important hours or even days. Specific and rapid markers of bacterial infection have been sought for use in the ICU. Mortality in critically ill patients increases gravely when Procalcitonin levels increase from day to day (own submitted, though yet unpublished data). Low PCT levels have been shown to effectively rule out sepsis.