Figures 1a and b show plasma concentrations of the four biomarkers in the patients admitted to ICU and separated into four categories. For all biomarkers differences were seen between the clinical categories as determined by Kruskal-Wallis ANOVA (p < 0.0001). The highest concentrations were measured in sepsis. For all four biomarkers the concentrations in sepsis were highly and significantly different from the other patient categories, except for plasma concentrations of HBP in the miscellaneous group which were similar to the concentrations in sepsis. The lowest concentrations were found in patients with trauma. The discrimination between sepsis and trauma was evaluated by ROC-analysis and showed equal AUCs of HNL Total and PCT whereas the AUCs of HNL Dimer and P-HBP were significantly smaller as compared to the AUC of P-HNL Total, p = 0.01 and p = 0.04, respectively (Fig. 2).
In Table 1 we show the relation of admission concentrations in all patients and sepsis patients separately to outcome in terms of the SOFA score (Sequential Organ Failure Assessment), the KDIGO score (The Kidney Disease: Improving Global Outcomes) and 30 days survival.
Table 1
The four biomarkers in relation to SOFA and KDIGO-scores and to survival. We show the results for the entire cohort and for sepsis only.
Biomarker All patients | SOFA score <8 or > 7 | p-value | KDIGO (Kruskal-Wallis) | 30 days survival, yes/no | |
HNL Total n = 243 | 48 vs 138 µg/L | P < 0.0001 | P < 0.0001 | 53 vs 107 µg/L | P < 0.0001 |
HNL Dimer n = 246 | 10.2 vs 16.8 µg/L | P < 0.0001 | P = 0.001 | 10.8 vs15.2 µg/L | P = 0.02 |
HBP n = 277 | 33 vs 51 µg/L | P < 0.0001 | P < 0.0001 | 34.6 vs 47.7 µg/L | P = 0.0007 |
PCT n = 180 | 0.27 vs 1.49 µg/L | P = 0.0001 | P < 0.0001 | 0.30 vs 0.46 µg/L | Ns |
Biomarker Sepsis | SOFA score < 8 or > 7 | p-value | KDIGO (Kruskal-Wallis) | 30 days survival, yes/no | |
HNL Total n = 69 | 91 vs 189 µg/L | P = 0.01 | P = 0.001 | 102 vs 168 µg/L | Ns |
HNL Dimer n = 64 | 16.2 vs 18.2 µg/L | Ns | Ns | 18.0 vs16.9 µg/L | Ns |
HBP n = 83 | 43 vs 70 µg/L | Ns | P = 0.03 | 47 vs 60 µg/L | Ns |
PCT n = 53 | 1.10 vs 3.57 µg/L | P = 0.008 | P = 0.005 | 1.47 vs 1.22 µg/L | Ns |
In the evaluation of the whole cohort, all four biomarkers were significantly related to SOFA-score and kidney function as evaluated by the KDIGO-score. Except for PCT, the biomarkers also showed significant differences between survivors and non-survivors. In the subgroup of patients with sepsis, HNL-Total and PCT showed significant associations to SOFA-score as well as to KDIGO. The latter was also seen for HBP. The HNL Dimer did not show such relations and none of the biomarkers showed significant differences between survivors and non-survivors in the sepsis cohort.
The relationship between SOFA-score and HNL Total and PCT are further illustrated in Fig. 2. For both biomarkers highly significant log-linear relationships to SOFA-score were seen (HNL-total r = 0.50 and for PCT r = 0.37). Not shown are the highly significant correlations (p < 0.001) between HPB (r = 0.40) and HNL Dimer (r = 0.32) to SOFA-score, respectively. In a multiple regression analysis including the four biomarkers in addition to sex and age, HNL Total independently related to the SOFA score in the whole cohort (p < 0.0001) and in patients with sepsis (p = 0.004).
In Fig. 3 the relationships of HNL Total and PCT to KDIGO are illustrated and show close relationships as was also seen for HPB and HNL Dimer in the whole cohort of patients (results not shown). Relations to KDIGO were also seen for HNL Total and PCT in the cohort of patients with sepsis, but only for HNL Total in miscellaneous and other medical disease, but not in patients with trauma in which only few patients had any signs of kidney failure. In a multiple regression analysis including the four biomarkers in addition to sex and age, HNL Total independently related to KDIGO in the whole cohort (p < 0.0001) and in patients with sepsis (p < 0.0001).
Monitoring of plasma biomarkers in ICU
Plasma samples were collected from all patients on three consecutive days. The results of the biomarkers are shown in Figs. 4a-d. In Fig. 4a the results of PCT are shown. Overall, there were no significant differences on PCT concentrations during these three days. Also shown in the figure are the results of patients with sepsis. By Friedman test, in which only paired samples were calculated on, we saw differences between the three days with slightly higher concentrations day 2, but a reduction in concentrations between day 2 and day 3 (p = 0.008, Wilcoxon´s test). However, when we compared the concentrations at the three days including all results on sepsis patients no significant differences were discerned (P = Ns, Mann-Whitney U-test) (Table 2).
Table 2
The four biomarkers are shown for the entire sepsis cohort. Per cent reductions as compared to admission day are shown. Comparisons between admission day and days 2 and 3, respectively, were calculated by the Mann-Whitney U test and statistical differences indicated by **=p < 0.01, ****=p < 0.00001.
| Admission day | Day 2 | Day 3 |
P-HNL Dimer | 17.3 (IQ 11.5–46) µg/L N = 69 100% | 13.5 (IQ 6.6–22) µg/L N = 62 78% ** | 8.5 (IQ 5.8–15) µg/L N = 33 49%**** |
P-HNL Total | 124 (IQ 70–246) µg/L N = 69 100% | 92 (IQ 54–200) µg/L N = 61 74% | 95 (IQ 49–161) µg/L N = 33 77% |
P-PCT | 1.27 (IQ 0.34–5.7) µg/L N = 59 100% | 1.38 (IQ 0.27–4.6) µg/L N = 55 109% | 1.49 (IQ 0.46–3.4) µg/L N = 31 117% |
P-HBP | 49 (IQ 33–99) µg/L N = 83 100% | 55 (IQ 31–108) µg/L N = 76 112% | 55 (26–88) µg/L N = 48 112% |
The plasma concentrations of HBP are shown for the whole cohort and for the sepsis cohort separately in Fig. 4b and Table 2. No changes in plasma concentrations in either group were seen during the three days follow-up.
Figure 4c shows the concentrations of HNL Total during the three days. Overall, no differences in plasma concentrations were seen. However, by Friedman test we saw a highly significant change in the sepsis group (P = 0.0006) with a reduction at day 2 (p = 0.0009, Wilcoxon´s test) as compared to day 1 and a further reduction at day 3 (p = 0.0006, Wilcoxon´s test). The reductions were 74% (day 2) and 77% (day 3) of the concentrations at admission day (Table 2).
Figure 4d shows the results of plasma concentrations of HNL Dimer. For the whole cohort (median 11.9 µg/L, IQ range 6.3–22 µg/L, n = 246) significant reductions were seen at days 2 (median 8.9 µg/L, IQ range 5.2–15.5 µg/L, n = 205) and 3 (median 7.5 µg/L, IQ range 5.4–12.9 µg/L, n = 102) (p < 0.0001, Wilcoxon´s test). In the sepsis group the changes in plasma concentrations from admission day to days 2 and 3 were highly significant (P < 0.00001, Friedman test). By paired tests between admission day (median 17.6 mg/ IQ range 14.2–25.9 µg/L, n = 58) and day 2 (median 13.7 mg/ IQ range 8.8–16.9 µg/L, n = 58) the changes were highly significant (p < 0.0001, Wilcoxon´s test) which was also the case for the changes between days 2 and 3 (p = 0.0009, Wilcoxon´s test). By the inclusion of all HNL Dimer results in the sepsis group a similar pattern emerged with a 49% reduction in the plasma concentrations at day 3 (Table 2). The changes in HNL Dimer after antibiotics treatment in relation to 30 mortality were evaluated in the whole ICU cohort and in sepsis separately. For the whole cohort the HNL Dimer concentrations at admission day among those who survived 30 days were 11.9 µg/L (IQ 6.2-23 µg/L) and at day 2, 8.4 µg/L (IQ 5.0-14.3 µg/L), n = 156, p < 0.0001 (Wilcoxon´s test for paired results). For those who died during the 30 days of observation the HNL Dimer concentrations at admission day were 13.6 µg/L (IQ 7.2-22 µg/L) and at day 2, 12.0 µg/L (IQ 6.8–21 µg/L), n = 42, p = Ns (Wilcoxon´s test for paired results). For the sepsis cohort the HNL Dimer concentrations at admission day among those who survived 30 days were 17.2 µg/L (IQ 7.7-48 µg/L) and at day 2, 13.7 µg/L (IQ 6.7–22 µg/L), n = 47, p < 0.0001 (Wilcoxon´s test for paired results). For those who died during the 30 days of observation the HNL Dimer concentrations at admission day were 15.3µg/L (IQ 11.8-27 µg/L) and at day 2, 13.1 µg/L (IQ 6.4-9 µg/L), n = 8, p = Ns (Wilcoxon´s test for paired results).
The differences between P-HNL Dimer and P-PCT during sepsis follow-up are further illustrated in Fig. 5. In the figure we show the highly significant reduction of P-HNL Dimer at day 2 after admission to the ICU in contrast to the non-significant changes in P-PCT. It is also seen in the figure that in the six patients with the very high P-HNL Dimer concentrations i.e. > 80 µg/L at admission day the reduction in concentrations was between 5-10-fold at day 2.