Table 4 NRI and IDI for assessing improvement in model performance after adding AFP-L2, AFP-L3 to predicting Trisomy 21,18.

From: Diagnostic value of maternal alpha-fetoprotein variants in second-trimester biochemical screening for trisomy 21 and 18

New method

Old method

IDI (%)

P value for IDI

NRI (%)

P value for NRI

Trisomy 21

AFP-L2

AFP

9.56

 < 0.001*

26.50

 < 0.001*

AFP-L3

AFP

12.34

 < 0.001*

26.70

 < 0.001*

AFP-L2 + AFP-L3

AFP

8.12

 < 0.001*

40.90

 < 0.001*

AFP + free β-hCG

AFP

14.88

 < 0.001*

37.40

 < 0.001*

AFP + free β-hCG

free β-hCG

9.51

 < 0.001*

10.54

0.008 **

AFP-L2 + free β-hCG

free β-hCG

7.86

 < 0.001*

15.61

 < 0.001*

AFP-L3 + free β-hCG

free β-hCG

12.15

 < 0.001*

17.21

 < 0.001*

AFP-L2 + AFP-L3 + free β-hCG

free β-hCG

7.97

 < 0.001*

27.57

 < 0.001*

AFP-L2 + free β-hCG

AFP-L2

3.67

0.003**

15.98

0.002 **

AFP-L2 + AFP-L3

AFP-L2

− 1.44

0.807

14.40

0.006 **

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2

3.78

0.012**

27.93

 < 0.001*

AFP-L3 + free β-hCG

AFP-L3

5.18

0.005**

17.38

0.002 **

AFP-L2 + AFP-L3

AFP-L3

− 4.22

0.978

14.21

0.005 **

AFP-L2 + AFP-L3 + free β-hCG

AFP-L3

1.00

0.319

27.74

 < 0.001*

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2 + free β-hCG

0.11

0.458

11.95

0.003**

AFP-L2 + AFP-L3 + free β-hCG

AFP-L3 + free β-hCG

− 4.18

1.000

10.35

0.002**

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2 + AFP-L3

5.22

 < 0.001*

13.53

0.002**

Trisomy 18

AFP-L2

AFP

− 8.12

0.998

− 13.84

0.947

AFP-L3

AFP

− 1.52

0.668

− 8.54

0.815

AFP-L2 AFP-L3

AFP

− 12.40

1.000

− 2.26

0.610

AFP + free β-hCG

AFP

17.35

 < 0.001*

31.05

 < 0.001*

AFP + free β-hCG

free β-hCG

18.55

 < 0.001*

0.19

0.478

AFP-L2 + free β-hCG

free β-hCG

17.05

 < 0.001*

2.10

0.150

AFP-L3 + free β-hCG

free β-hCG

9.81

 < 0.001*

− 1.57

0.786

AFP-L2 + AFP-L3 + free β-hCG

free β-hCG

− 0.75

0.707

0.71

0.366

AFP-L2 + free β-hCG

AFP-L2

23.97

 < 0.001*

46.80

 < 0.001*

AFP-L2 + AFP-L3

AFP-L2

− 4.28

0.954

11.58

0.072

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2

6.17

0.005**

45.42

 < 0.001*

AFP-L3 + free β-hCG

AFP-L3

10.12

0.001**

37.83

 < 0.001*

AFP-L2 + AFP-L3

AFP-L3

− 10.88

0.999

6.28

0.220

AFP-L2 + AFP-L3 + free β-hCG

AFP-L3

− 0.44

0.551

40.11

 < 0.001*

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2 + free β-hCG

− 17.81

1.000

− 1.39

0.688

AFP-L2 + AFP-L3 + free β-hCG

AFP-L3 + free β-hCG

− 10.56

1.000

2.28

0.001**

AFP-L2 + AFP-L3 + free β-hCG

AFP-L2 + AFP-L3

10.44

 < 0.001*

33.84

 < 0.001*

  1. AFP, alpha-fetoprotein; free β-hCG, free beta subunit of human chorionic gonadotropin; AFP-L2, α-fetoprotein heterogeneity L2; AFP-L3, α-fetoprotein heterogeneity L3; IDI, Integrated Discrimination Improvement; NRI, Net Reclassification Improvement. *P < 0.001, **P < 0.05.
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