Our results indicate that PCT concentrations are associated with the severity of MODS as assessed by the SOFA score. These results are in general agreement with studies in which PCT levels were compared with the severity of sepsis by sepsis-related score systems. The similar observations made by sepsis-related score systems of the inflammatory response and MODS-weighted score systems can be explained by similar pathophysiological alterations occurring during advanced states of sepsis and MODS. Increasing PCT concentrations were previously reported by Zeni et al  and Oberhoffer et al  during more severe stages of sepsis (severe sepsis and septic shock) as defined by the ACCP/SCCM criteria [7,20]. Also, other authors observed high concentrations of PCT during septic shock, and comparable low concentrations during SIRS or less severe systemic inflammation. In a study by Al-Nawas et al , very low PCT concentrations were measured during SIRS, but high concentrations when septic shock was diagnosed. Similar results were published by Gramm et al  and by other authors [1,9].
None of these authors, however, analyzed the severity of multiple organ dysfunction rather than the severity of sepsis and systemic inflammation and there are no data available as to the relation of PCT concentrations and the severity of multiple organ dysfunction during systemic inflammation. By using the SOFA score, we thus focused particularly on the extent of multiorgan dysfunction rather than the severity or type of inflammatory response or infection. This approach is closer to clinical conditions, since in severely ill patients the presence or absence of a significant infection cannot always be specified .
With increasing categories of the SOFA score, reflecting the severity of MODS, higher PCT concentrations were observed. However, PCT should not serve as a surrogate marker for the severity of MODS, since the correlation of PCT concentrations and score values is weak.
These findings have an impact on the interpretation and design of comparative clinical studies using PCT. When PCT levels are to be compared between different groups of patients, eg for purposes of differential diagnosis, assessment of the severity of the disease and of systemic inflammation, including the severity of MODS, is mandatory. When patients were not stratified clearly enough for severity of MODS and systemic inflammation in clinical studies, imbalances between groups as to the severity of MODS or sepsis may significantly influence the significance of different PCT concentrations between the respective groups. We therefore suggest that in future studies score systems evaluating not only the severity of systemic inflammation, but also of MODS should be assessed along with PCT concentrations. This way, imbalances between groups as to severity of inflammation or MODS can be minimized.
PCT has several advantages in severely ill patients compared with CRP. The most striking one, demonstrated in this study, is the enormous range of PCT reactivity resulting in a marked increase in PCT plasma levels, especially during severe stages of MODS and systemic inflammation. On the other hand, PCT concentrations are quite low when only a moderate organ dysfunction or a weak systemic inflammatory response is present. In contrast, CRP levels are often found to be already increased to maximal concentrations in patients with low SOFA scores. Thus, CRP cannot provide information as to further increases in organ dysfunction and the inflammatory progress, respectively, since it is already increased to its maximum values during a less severe stage of disease. Further advantages of PCT are its more rapid kinetics; PCT reacts faster than CRP both during an increase or decrease of inflammation. Although data were not presented, a more rapid increase of PCT was observed also in this study . This observation was already described by several authors and thus is not focused on within this study, eg after experimental administration of lipopolysaccharide  or accidental application of a microbial contaminated infusion , where PCT increased within 6h after the initial stimulus and CRP did not significantly increase before 12h after onset of induction. Also, under clinical conditions, a more rapid increase of PCT compared with CPR was described after the onset of severe inflammation . Moreover, the decline of PCT concentrations occurs more rapidly than that of CRP [2,23]. In this study, a rapid decline of PCT levels in patients who recovered and survived was also observed (Fig 3), whereas CRP increased for several days even after recovery and discharge of the patient from the intensive care unit (Fig 4).
Regarding the prognosis of the disease, the course of PCT after day 4 from the onset of systemic inflammation was able to distinguish survivors from non-survivors. Until day 4, PCT concentrations were not statistically different in the groups. Likewise, the initial height of the PCT concentrations did not correlate with the further course of the disease. The results of this analysis should not be over-interpreted. The number of patients is too small and too heterogeneous for a general conclusion regarding the absolute height of PCT concentrations and estimating the prognosis of the disease by PCT. In a clinical study, Ober-hoffer et al report high PCT levels in patients with poor prognosis already during the onset of the disease . Further studies support the notion that the course of PCT concentrations rather than the absolute height is a mirror of the systemic inflammatory response and plays a major role for prognosis [4,10,18,19]. Also with regard to this aspect, PCT is superior to CRP, since patients with a lethal outcome were not distinguished by CRP at any time in our study. A recently conducted animal study by Nylen et al  suggests that PCT might be a significant lethal factor during sepsis. In this experimental study, PCT significantly increased mortality in a hamster endotoxin shock model, and anti-PCT reactive antiserum was protective as to survival.
In summary, PCT compared with CRP is characterized by its ability to be induced to very high serum concentrations also during advanced stages of MODS and severe systemic inflammation, respectively, whereas CRP is often already in the upper concentration range, even in patients with low severity scores, and exhibits no such further dynamics during the course of MODS and systemic inflammation. PCT more rapidly declines to the normal range during the recovery of the patient compared with CRP, and thus provides more information in patients with MODS and sepsis of various etiology than CRP. The absolute height of PCT concentrations in the initial period of inflammation was found to be less important than the further course of its plasma concentrations. The strong association of high PCT concentrations with both the SOFA and the APACHE II score indicates that not only sepsis-related score systems, but also a MODS-related evaluation of the severity of the diseases should be considered when PCT concentrations of different types of disease were compared.