Table 1 Characteristics of the included patients between the testing set and the training set groups

Age, years, Mean ± SD

78.44 ± 7.76

78.97 ± 7.47

78.16 ± 7.91

t = 1.24

Gender, n (%)

χ² = 1.105

 Female

296 (47.82)

110 (50.69)

186 (46.27)

 Male

323 (52.18)

107 (49.31)

216 (53.73)

Marital status, n (%)

χ² = 1.536

 Divorced

34 (5.49)

15 (6.91)

19 (4.73)

 Married

298 (48.14)

105 (48.39)

193 (48.01)

 Separated

3 (0.48)

1 (0.46)

2 (0.50)

 Single

111 (17.93)

39 (17.97)

72 (17.91)

 Widowed

173 (27.95)

57 (26.27)

116 (28.86)

Ethnicity, n (%)

χ² = 7.042

 Asian

29 (4.68)

12 (5.53)

17 (4.23)

 Black

62 (10.02)

19 (8.76)

43 (10.70)

 Hispanic

15 (2.42)

7 (3.23)

8 (1.99)

 Other

14 (2.26)

9 (4.15)

5 (1.24)

 White

499 (80.61)

170 (78.34)

329 (81.84)

Respiratory rate, times/min, Mean ± SD

22.61 ± 6.94

22.41 ± 7.13

22.71 ± 6.84

t = − 0.52

Temperature, °C, Mean ± SD

36.80 ± 1.00

36.79 ± 0.99

36.80 ± 1.01

t = − 0.19

Heart rate, beats/min, Mean ± SD

95.65 ± 20.71

93.55 ± 20.03

96.79 ± 21.01

t = − 1.86

SBP, mmHg, Mean ± SD

121.75 ± 24.48

120.47 ± 26.35

122.45 ± 23.42

t = − 0.93

DBP, mmHg, Mean ± SD

61.67 ± 17.38

60.40 ± 17.73

62.36 ± 17.17

t = − 1.34

MAP, mmHg, M (Q₁, Q₃)

76.00 (67.00, 88.00)

74.00 (65.00, 88.00)

77.00 (67.67, 88.00)

Z = − 1.035

SpO2, % Mean ± SD

95.85 ± 6.33

95.69 ± 7.55

95.94 ± 5.57

t = − 0.43

WBC, K/Ul, M (Q₁, Q₃)

12.30 (8.70, 17.50)

12.90 (8.80,18.30)

12.00 (8.50,17.10)

Z = 1.510

RBC, m/uL, Mean ± SD

3.84 ± 0.72

3.79 ± 0.73

3.87 ± 0.71

t = − 1.17

Sodium, mEq/L, Mean ± SD

138.02 ± 6.19

137.95 ± 6.49

138.05 ± 6.03

t = − 0.19

Potassium, mEq/L, Mean ± SD

4.52 ± 0.89

4.54 ± 0.83

4.51 ± 0.93

t = 0.39

Phosphate, mg/dL, M (Q₁, Q₃)

3.50 (2.90, 4.30)

3.50 (3.00, 4.50)

3.40 (2.80, 4.20)

Z = 1.840

Calcium, mg/dL, Mean ± SD

8.46 ± 0.91

8.53 ± 0.83

8.42 ± 0.95

t = 1.46

pH, Mean ± SD

7.36 ± 0.11

7.36 ± 0.11

7.37 ± 0.11

t = − 1.07

Lactate, mmol/L, M (Q₁, Q₃)

2.00 (1.50, 2.90)

1.90 (1.40, 2.90)

2.00 (1.50, 2.90)

Z = − 0.634

INR, M (Q₁, Q₃)

1.20 (1.10, 1.60)

1.20 (1.10, 1.60)

1.30 (1.10, 1.60)

Z = − 0.195

MCV, μm³, Mean ± SD

91.10 ± 7.26

91.26 ± 7.64

91.01 ± 7.05

t = 0.41

magnesium, mg/dL, Mean ± SD

1.94 ± 0.39

1.96 ± 0.42

1.93 ± 0.37

t = 1.09

BUN, mg/dL, M (Q₁, Q₃)

29.00 (20.00, 43.00)

29.00 (20.00, 46.00)

29.00 (20.00, 43.00)

Z = 0.464

Creatine kinase, IU/L, M (Q₁, Q₃)

76.00 (38.00, 161.00)

63.00 (34.00, 137.00)

80.50 (40.00, 181.00)

Z = − 2.829

Hematocrit, %, Mean ± SD

34.79 ± 6.13

34.40 ± 6.12

35.00 ± 6.14

t = − 1.16

PO2, M (Q₁, Q₃)

84.00 (63.00, 133.00)

81.00 (62.00, 135.00)

85.50 (63.00, 129.00)

Z = − 0.492

Hemoglobin, g/dL, Mean ± SD

11.45 ± 2.07

11.30 ± 2.05

11.54 ± 2.08

t = − 1.38

PCO2, M (Q₁, Q₃)

42.00 (35.00, 52.00)

43.00 (35.00, 54.00)

42.00 (34.00, 51.00)

Z = 0.699

RDW, %, Mean ± SD

15.47 ± 2.19

15.55 ± 2.24

15.43 ± 2.16

t = 0.64

COPD, n (%)

χ² = 0.000

 No

479 (77.38)

168 (77.42)

311 (77.36)

 Yes

140 (22.62)

49 (22.58)

91 (22.64)

Lung cancer, n (%)

χ² = 3.392

 No

592 (95.64)

212 (97.70)

380 (94.53)

 Yes

27 (4.36)

5 (2.30)

22 (5.47)

AF, n (%)

χ² = 0.395

 No

350 (56.54)

119 (54.84)

231 (57.46)

 Yes

269 (43.46)

98 (45.16)

171 (42.54)

Liver cirrhosis, n (%)

χ² = 0.910

 No

604 (97.58)

210 (96.77)

394 (98.01)

 Yes

15 (2.42)

7 (3.23)

8 (1.99)

CHF, n (%)

χ² = 0.149

 No

293 (47.33)

105 (48.39)

188 (46.77)

 Yes

326 (52.67)

112 (51.61)

214 (53.23)

Heart disease, n (%)

χ² = 2.605

 No

514 (83.04)

173 (79.72)

341 (84.83)

 Yes

105 (16.96)

44 (20.28)

61 (15.17)

DM, n (%)

χ² = 0.001

 No

474 (76.58)

166 (76.50)

308 (76.62)

 Yes

145 (23.42)

51 (23.50)

94 (23.38)

Respiratory failure, n (%)

χ² = 0.801

 No

243 (39.26)

80 (36.87)

163 (40.55)

 Yes

376 (60.74)

137 (63.13)

239 (59.45)

Hyperlipidemia, n (%)

χ² = 0.018

 No

393 (63.49)

137 (63.13)

256 (63.68)

 Yes

226 (36.51)

80 (36.87)

146 (36.32)

Renal failure, n (%)

χ² = 0.110

 No

268 (43.30)

92 (42.40)

176 (43.78)

 Yes

351 (56.70)

125 (57.60)

226 (56.22)

Malignant cancer, n (%)

χ² = 0.009

 No

395 (63.81)

139 (64.06)

256 (63.68)

 Yes

224 (36.19)

78 (35.94)

146 (36.32)

SAPSII, Mean ± SD

44.65 ± 13.24

44.78 ± 13.09

44.58 ± 13.34

t = 0.18

SOFA, M (Q₁, Q₃)

5.00 (3.00, 7.00)

5.00 (3.00, 7.00)

5.00 (3.00,7.00)

Z = 1.165

Septic shock, n (%)

χ² = 0.492

 No

500 (80.78)

172 (79.26)

328 (81.59)

 Yes

119 (19.22)

45 (20.74)

74 (18.41)

Ventilation, n (%)

χ² = 0.153

 No

269 (43.46)

92 (42.40)

177 (44.03)

 Yes

350 (56.54)

125 (57.60)

225 (55.97)

Vesopressor, n (%)

χ² = 0.889

 No

583 (94.18)

207 (95.39)

376 (93.53)

 Yes

36 (5.82)

10 (4.61)

26 (6.47)

Streptococcus pneumoniae, n (%)

χ² = 1.083

 No

597 (96.45)

207 (95.39)

390 (97.01)

 Yes

22 (3.55)

10 (4.61)

12 (2.99)

Klebsiella pneumoniae, n (%)

χ² = 0.019

 No

583 (94.18)

204 (94.01)

379 (94.28)

 Yes

36 (5.82)

13 (5.99)

23 (5.72)

Virus, n (%)

χ² = 1.020

 No

602 (97.25)

213 (98.16)

389 (96.77)

 Yes

17 (2.75)

4 (1.84)

13 (3.23)

Emphysema, n (%)

χ² = 0.219

 No

593 (95.80)

209 (96.31)

384 (95.52)

 Yes

26 (4.20)

8 (3.69)

18 (4.48)

Pneumothorax, n (%)

χ² = 0.008

 No

608 (98.22)

213 (98.16)

395 (98.26)

 Yes

11 (1.78)

4 (1.84)

7 (1.74)

Effusion, n (%)

χ² = 0.350

 No

544 (87.88)

193 (88.94)

351 (87.31)

 Yes

75 (12.12)

24 (11.06)

51 (12.69)

Yeast, n (%)

χ² = 0.479

 No

414 (66.88)

149 (68.66)

265 (65.92)

 Yes

205 (33.12)

68 (31.34)

137 (34.08)

Staphylococcus, n (%)

χ² = 1.446

 No

432 (69.79)

158 (72.81)

274 (68.16)

 Yes

187 (30.21)

59 (27.19)

128 (31.84)

EColi, n (%)

χ² = 7.523

 No

583 (94.18)

212 (97.70)

371 (92.29)

 Yes

36 (5.82)

5 (2.30)

31 (7.71)

Other bacteria, n (%)

χ² = 0.017

 No

447 (72.21)

156 (71.89)

291 (72.39)

 Yes

172 (27.79)

61 (28.11)

111 (27.61)

Another streptococcus, n (%)

χ² = 0.831

 No

586 (94.67)

203 (93.55)

383 (95.27)

 Yes

33 (5.33)

14 (6.45)

19 (4.73)

Candida, n (%)

χ² = 1.499

 No

587 (94.83)

209 (96.31)

378 (94.03)

 Yes

32 (5.17)

8 (3.69)

24 (5.97)

Acinetobacter, n (%)

–

 No

613 (99.03)

215 (99.08)

398 (99.00)

 Yes

6 (0.97)

2 (0.92)

4 (1.00)

Clostridium, n (%)

χ² = 0.744

 No

596 (96.28)

207 (95.39)

389 (96.77)

 Yes

23 (3.72)

10 (4.61)

13 (3.23)

Citrobacter, n (%)

–

 No

617 (99.68)

216 (99.54)

401 (99.75)

 Yes

2 (0.32)

1 (0.46)

1 (0.25)

Enterococcus, n (%)

χ² = 0.088

 No

562 (90.79)

196 (90.32)

366 (91.04)

 Yes

57 (9.21)

21 (9.68)

36 (8.96)

PCP, n (%)

χ² = 1.730

 No

617 (99.68)

217 (100.00)

400 (99.50)

 Yes

2 (0.32)

0 (0.00)

2 (0.50)

Fungus, n (%)

–

 No

615 (99.35)

215 (99.08)

400 (99.50)

 Yes

4 (0.65)

2 (0.92)

2 (0.50)

CURB-65, Mean ± SD

2.55 ± 0.81

2.60 ± 0.82

2.52 ± 0.80

t = 1.17

PSI, Mean ± SD

136.63 ± 27.27

136.91 ± 28.73

136.48 ± 26.49

t = 0.19

NLR, M (Q₁, Q₃)

10.40 (5.99, 18.52)

10.71 (6.20, 17.40)

9.92 (5.97, 19.98)

Z = − 0.037

PLR, M (Q₁, Q₃)

2.78 (1.70, 4.61)

2.90 (1.77, 4.30)

2.75 (1.69, 4.74)

Z = 0.112

SOAR, M (Q₁, Q₃)

2.00 (1.00, 2.00)

2.00 (1.00, 2.00)

2.00 (1.00, 2.00)

Z = − 0.671

HPR, M (Q₁, Q₃)

0.04 (0.03, 0.06)

0.04 (0.03, 0.06)

0.05 (0.03, 0.06)

Z = − 2.377

Elixhauser comorbidity score, M (Q₁, Q₃)

20.00 (12.00, 29.00)

21.00 (14.00, 29.00)

20.00 (12.00, 29.00)

Z = 0.767

PNI, Mean ± SD

31.63 ± 8.01

31.58 ± 6.04

31.65 ± 8.90

t = − 0.13

RDW/BUN ratio, Mean ± SD

5.29 ± 1.54

5.25 ± 1.45

5.32 ± 1.59

t = − 0.50

dNLR, Mean ± SD

− 1.01 ± 0.07

− 1.01 ± 0.01

− 1.01 ± 0.09

t = − 0.15

BUN/ALB ratio, M (Q₁, Q₃)

9.71 (6.28, 14.44)

10.00 (6.32, 14.62)

9.63 (6.21, 14.40)

Z = 0.392

ALB, Mean ± SD

3.07 ± 0.62

3.09 ± 0.60

3.06 ± 0.64

t = 0.61

Anion gap, Mean ± SD

63.03 ± 9.69

63.22 ± 10.35

62.93 ± 9.32

t = 0.36

ICU LOS, M (Q₁, Q₃)

3.20 (1.73, 7.58)

3.13 (1.77, 7.58)

3.25 (1.72, 7.43)

Z = − 0.409

In hospital mortality, n (%)

χ² = 0.104

 No

464 (74.96)

161 (74.19)

303 (75.37)

 Yes

155 (25.04)

56 (25.81)

99 (24.63)