A total of 1747 acute medical patients were included. Median age was 70 (IQR: 57–79) and 51.4% were men. Table 1 shows baseline characteristics for all patients and for patients stratified by baseline suPAR < 4, ≥ 4 - ≤6 and suPAR > 6 ng/ml. Almost half of the patients (48.3%) had a suPAR below 4 ng/ml. suPAR increases with age whereas sex did not change significantly across the groups (Table 1). Patients that presented with comorbidities (Diabetes 1 or 2 (DM), cardiovascular disease (CVD), neurological disease (NEU) or pulmonary disease (PULM) had generally elevated suPAR levels (Table 1).
Table 1
|
All
|
suPAR < 4
|
suPAR 4–6
|
suPAR > 6
|
P value
|
N (%)
|
1747
|
804 (46.0)
|
514 (29.4)
|
429 (24.6)
|
|
Age median (IQR)
|
70 (57–79)
|
62 (44–73)
|
74 (65–83)
|
76 (67–85)
|
< 0.001
|
Sex (= male %)
|
897 (51.4)
|
436 (55.2)
|
250 (48.6)
|
211 (49.2)
|
0.08
|
suPAR ng/ml (IQR)
|
4.1 (3.3-6.0)
|
3.2 (2.9–3.6)
|
4.7 (4.3–5.3)
|
8.5 (7.1–11.3)
|
< 0.001
|
CRP ug/ml (IQR)
|
3 (3–17)
|
3 (3–4)
|
4 (3–18)
|
20 (5–72)
|
< 0.001
|
Lymphocyte count 103/ul (IQR)
|
7.5 (6.0-9.8)
|
7.3 (5.9–8.8)
|
7.7 (5.9–9.8)
|
8.55 (6.3–12.1)
|
< 0.001
|
Creatinine (IQR) nmol/ml
|
77 (64–96)
|
70 (61–83)
|
79.5 (65–97)
|
101 (74–139)
|
< 0.001
|
Comorbidities
|
|
Diabetes N (%)
|
365 (20.9)
|
109 (13.6)
|
121 (23.5)
|
135 (31.5)
|
< 0.001
|
Cardiovascular disease N (%)
|
1151 (65.9)
|
416 (51.7)
|
387 (75.3)
|
348 (81.1)
|
< 0.001
|
Neurological disorder N (%)
|
516 (29.5)
|
209 (26.0)
|
156 (30.4)
|
151 (35.2)
|
0.003
|
Pulmonary disease N (%)
|
388 (22.2)
|
155 (19.3)
|
126 (24.5)
|
107 (24.9)
|
0.024
|
Readmission and suPAR
In all 379 (21.7%) of the patients had been admitted to the hospital within 30-days prior to the study inclusion. Patients that had a prior admission had higher suPAR levels at baseline (29.6% among patients with suPAR above 6 ng/ml versus 16.3% of patients with suPAR below 4 ng/ml, p < 0.001, Table 2). In contrast to this, there was no significant difference in 30-day readmission following baseline suPAR measurement (23.9 % among patients with suPAR above 6 ng/ml versus 19.0% of patients with suPAR below 4 ng/ml, p = 0.14) (Table 2).
Table 2
Outcomes and outcomes in relation to suPAR cut-offs
|
All
|
suPAR < 4 ng/ml
|
suPAR 4–6
|
suPAR > 6 ng/ml
|
P value
|
N
|
1747
|
804
|
514
|
429
|
|
Discharge < 24 H N (%)
|
785 (44.9)
|
462 (57.5)
|
215 (41.8)
|
108 (25.2)
|
< 0.001
|
30 Day pre-admitted N (%)
|
379 (21.7)
|
131 (16.3)
|
121 (23.5)
|
127 (29.6)
|
< 0.001
|
Readmission 30 Days N (%)
|
368 (21.1)
|
153 (19.0)
|
114 (22.2)
|
101 (23.5)
|
0.14
|
Mortality 7 Days N (%)
|
34 (1.95)
|
3 (0.37)
|
9 (1.75)
|
22 (5.13)
|
< 0.001
|
Mortality 30 Days N (%)
|
81 (4.64)
|
6 (0.75)
|
25 (4.9)
|
50 (11.7)
|
< 0.001
|
Mortality 90 Days N (%)
|
138 (7.90)
|
8 (1.0)
|
43 (8.4)
|
87 (20.3)
|
< 0.001
|
Association with suPAR and 30 and 90-day mortality
During 30-day follow-up, 81 (4.6%) patients died and this number increased to 138 (7.9%) after 90 days. Patients with suPAR below 4 ng/ml had lower risk of mortality, both with regard to 30- and 90-day mortality (both p < 0.001, Table 2). With regard to 90-day mortality, we observed a 20-fold higher mortality in patients with suPAR above 6 ng/ml (87 died out 429, 20.3%), compared to below 4 ng/ml (8 died out of 804 patients, 1.0%) (Table 2).
Prediction of 90-day mortality using ROC AUC analysis
We investigated the predictive value of suPAR using ROC analysis and calculated the Area under the Curve (AUC). As shown in Fig. 1, age, CRP and suPAR all were associated with 90-day mortality, with AUC’s (95%CI) of 0.77 (0.74–0.81), 0.75 (0.71–0.79) and 0.80 (0.77–0.83), respectively.
Adjusted Cox regression analysis
To determine whether the association between suPAR and mortality was independent of age, sex, and CRP levels, multivariate regression analysis was carried out including log2 suPAR (per 100% increase (doubling) in suPAR). For every doubling in suPAR, the Odds ratio for 90-day mortality increased with 1.96 (95% confidence intervals: 1.42–2.70) showing that suPAR independent of age sex and CRP was associated with 90-day mortality. Compared to having suPAR below 4 ng/ml, patients with suPAR above 6 ng/ml had a sex- and age-adjusted Odds ratio of 13.2 (95%CI: 6.6–30.3). Patients with suPAR equal to or between 4 and 6 ng/ml had an increased Odds ratio of 2.4 (95%CI: 1.6–3.7) compared to patients with suPAR below 4 ng/ml.
Sensitivity, specificity, NPV and PPV for suPAR cut-offs and 30- and 90-day mortality
Of the 804 patients with suPAR below 4 ng/ml, 6 died (0.7%) within 30-days of admission resulting in a negative predictive value of 99.3%. Among patients with suPAR above 6 ng/ml (N = 429), 50 patients died within 30 days (11.7%), corresponding to a positive predictive value of 11.6% and a specificity of 77.4%. With regard to 90-day mortality, 8 out of 804 (1.0%) with suPAR below 4 ng/ml died resulting in a NPV of 99.0% and a sensitivity of 94.6%. In patients with suPAR above 6 ng/ml, a PPV of 20.1% and a specificity of 78.7% was observed. Tables 3 and 4 shows sensitivity, specificity and NPV and PPV for 30- and 90-day mortality at the suPAR cut-off of 4 ng/ml and suPAR cut-off at 6 ng/ml, respectively.
Table 3
NPV, PPV, sensitivity and specificity at cut-off 4 ng/ml. NPV: Negative predictive value; PPV: Positive Predictive value
|
All
|
suPAR < 4 ng/ml
|
suPAR = > 4 ng/ml
|
NPV %
|
PPV %
|
Sensitivity %
|
Specificity %
|
N
|
1747
|
804
|
943
|
|
|
|
|
Mortality 30 Days
N (%)
|
81 (4.6)
|
6 (0.75)
|
75 (8.0)
|
99.3
|
7.95
|
92.6
|
47.9
|
Mortality 90 Days
N (%)
|
138 (7.9)
|
8 (1.0)
|
130 (13.8)
|
99.0
|
13.8
|
94.2
|
49.5
|
Table 4
NPV, PPV, sensitivity and specificity at cut-off 6 ng/ml. NPV: Negative predictive value; PPV:Positive Predictive value
|
All
|
suPAR < = 6 ng/ml
|
suPAR > 6 ng/ml
|
NPV %
|
PPV %
|
Sensitivity %
|
Specificity %
|
N
|
1747
|
1318
|
429
|
|
|
|
|
Mortality 30 Days
N (%)
|
81 (4.6)
|
31 (2.4)
|
50 (11.7)
|
97.6
|
11.7
|
61,7
|
77,3
|
Mortality 90 Days
N (%)
|
138 (7.9)
|
51 (3.9)
|
87 (20.3)
|
96.3
|
20.3
|
63.0
|
78,7
|