Table 3 Associations and difference in diagnostic accuracy between disc height and ‘LBP year’ at different thresholds and ages. Associations are expressed as odds ratios (OR) with 95% confidence intervals (95% CI) obtained from logistic regression analyses adjusted for body mass index. The probability of no difference in Area Under Curves (AUC) between Thresholds 1, 2 and 3 is reported as p-values from chi square tests. More details are given in Additional File 5

All participants (n = 409)

1.44 (0.89;2.35)

2.53 (1.64;3.90)*

2.29 (0.49;10.63)

AUC T1 = AUC T2: 0.004*

AUC T2 = AUC T3: 0.006*

AUC T1 = AUC T3: 0.760

 Men (n = 197)

2.14 (1.02;4.49)*

3.96 (2.11;7.43)*

1.82 (0.20;16.80)

AUC T1 = AUC T2: 0.001*

AUC T2 = AUC T3: 0.000*

AUC T1 = AUC T3: 0.121

 Women (n = 210)

1.09 (0.55;2.14)

1.73 (0.94;3.18)

2.12 (0.24;18.55)

AUC T1 = AUC T2: 0.001*

AUC T2 = AUC T3: 0.004*

AUC T1 = AUC T3: 0.586

 Upper lumbar spine (n = 409)

1.44 (0.88;2.36)

3.68 (1.62;8.38)*

–

AUC T1 = AUC T2: 0.097

 Lower lumbar spine (n = 409)

1.49 (0.94;2.38)

2.31 (1.49;3.57)*

2.00 (0.42;9.42)

AUC T1 = AUC T2: 0.019

AUC T2 = AUC T3: 0.01*

AUC T1 = AUC T3: 0.519

Disc height at 45 Years

Threshold 1: ≥ grade 1

(n = 237) (69.50%)

OR (95% CI)

Threshold 2: ≥ grade 2

(n = 168) (49.27%)

OR (95% CI)

Threshold 3: = grade 3

(n = 14) (4.11%)

OR (95% CI)

AUC comparison (p-value)

All participants (n = 341)

1.05 (0.64;1,74)

0.97 (0.61;1,55)

0.43 (0.15;1.26)

AUC T1 = AUC T2: 0.724

AUC T2 = AUC T3: 0.296

AUC T1 = AUC T3: 0.275

 Men (n = 160)

1.53 (0.73;3.21)

1.17 (0.59;2.29)

1.13 (0.21;6.09)

AUC T1 = AUC T2: 0.725

AUC T2 = AUC T3: 0.954

AUC T1 = AUC T3: 0.795

 Women (n = 181)

0.77 (0.39;1.55)

0.83 (0.43;1.58)

0.16 (0.03;0.87)*

AUC T1 = AUC T2: 0.929

AUC T2 = AUC T3: 0.441

AUC T1 = AUC T3: 0.540

 Upper lumbar spine (n = 341)

1.51 (0.86;2.64)

1.94 (0.93;4.06)

–

AUC T1 = AUC T2: 0.735

 Lower lumbar spine (n = 341)

0.99 (0.62;1.60)

0.96 (0.60;1.54)

0.43 (0.15;1.26)

AUC T1 = AUC T2: 0.896

AUC T2 = AUC T3: 0.284

AUC T1 = AUC T3: 0.302

Disc height at 49 Years

Threshold 1: ≥ grade 1

(n = 238) (84.40%)

OR (95% CI)

Threshold 2: ≥ grade 2

(n = 187) (66.31%)

OR (95% CI)

Threshold 3: = grade 3

(n = 29) (10.28%)

OR (95% CI)

AUC comparison (p-value)

All participants (n = 282)

2.49 (1.28;4.85)*

1.84 (1.08;3.13)*

0.89 (0.38;2.06)

AUC T1 = AUC T2: 0.995

AUC T2 = AUC T3: 0.134

AUC T1 = AUC T3: 0.070

 Men (n = 132)

3.22 (1.27;8.16)*

2.20 (1.04;4.64)*

1.73 (0.51;5.84)

AUC T1 = AUC T2: 0.864

AUC T2 = AUC T3: 0.046*

AUC T1 = AUC T3: 0.019*

 Women (n = 150)

1.69 (0.61;4.68)

1.57 (0.72;3.42)

0.44 (0.13;1.48)

AUC T1 = AUC T2: 0.876

AUC T2 = AUC T3: 0.081

AUC T1 = AUC T3: 0.074

 Upper lumbar spine (n = 282)

3.69 (2.00;6.81)*

4.77 (2.17;10.49)*

–

AUC T1 = AUC T2: 0.448

 Lower lumbar spine (n = 282)

1.74 (0.95;3.17)

1.50 (0.89;2.52)

0.89 (0.38;2.10)

AUC T1 = AUC T2: 0.971

AUC T2 = AUC T3: 0.233

AUC T1 = AUC T3: 0.202