Table 1 Study population characteristics and distribution of answers of the screening tool among the different groups n (%)

Age

41.8 ± 14.4

60.0 ± 12.5

 < 0.001

41.8 ± 14.4

33.1 ± 12.4

0.010

Age at onset disease

37.5 ± 12.5

55.7 ± 10.9

 < 0.001

37.5 ± 12.5

41.4 ± 12.8

0.146

Sex

0.460

 Male

28 (56.0)

43 (28.7)

28 (56.0)

116 (58.0)

 Female

22 (44.0)

107 (71.3)

22 (44.0)

84 (42.0)

Do you have joint pain?

 < 0.001

 < 0.001

 No

27(54.0)

16(10.7)

27(54.0)

172(86.0)

 Yes

23(46.0)

134(89.3)

23(46.0)

28(14.0)

Do you have joint swelling?

0.104

 < 0.001

 No

27(54.0)

98(65.3)

27(54.0)

197(98.5)

 Yes

23(46.0)

52(34.7)

23(46.0)

3(1.5)

Do you have joint swelling in more than 3 joints?

0.167

0.026

 No

44(88.0)

121(80.7)

44(88.0)

193(96.5)

 Yes

6(12.0)

29(19.3)

6(12.0)

7(3.5)

Are your legs affected ?

0.267

0.393

 No

43(86.0)

121(80.7)

43(86.0)

166(83.0)

 Yes

7(14.0)

29(19.3)

7(14.0)

34(17.0)

Do you have back pain?

 < 0.001

 < 0.001

 No

8(16.0)

77(51.3)

8(16.0)

159(79.5)

 Yes

42(84.0)

73(48.7)

42(84.0)

41(20.5)

Do you have stiffness in back lasting for > 30?

 < 0.001

 < 0.001

 No

7(14.0)

143(95.3)

7(14.0)

199(99.5)

 Yes

43(86.0)

7(4.7)

43(86.0)

1(0.5)

Do you have back pain a wakening you the 2^nd half of the night?

 < 0.001

 < 0.001

 No

11(22.0)

147(98.0)

11(22.0)

192(96.0)

 Yes

39(78.0)

3(2.0)

39(78.0)

8(4.0)

Does physical exercise improve your back pain?

 < 0.001

 < 0.001

 No

12(24.0)

146(97.3)

12(24.0)

182(91.0)

 Yes

38(76.0)

4(2.7)

38(76.0)

18(9.0)

Does NSAIDs improve your back pain?

 < 0.001

 < 0.001

 No

7(14.0)

132(88.0)

7(14.0)

173(86.5)

 Yes

43(86.0)

18(12.0)

43(86.0)

27(13.5)

Do you have anterior chest pain?

0.062

0.557

 No

48(96.0)

150(100.0)

48(96.0)

190(95.0)

 Yes

2(4.0)

0(0.0)

2(4.0)

10(5.0)

Do you have buttock pain?

 < 0.001

 < 0.001

 No

21(42.0)

149(99.3)

21(42.0)

192(96.0)

 Yes

29(58.0)

1(0.7)

29(58.0)

8(4.0)

Do you have red eyes now/in past?

 < 0.001

0.007

 No

36(72.0)

150(100.0)

36(72.0)

176(88.0)

 Yes

14(28.0)

0(0.0)

14(28.0)

24(12.0)

Do you have heel pain?

 < 0.001

 < 0.001

 No

30(60.0)

147(98.0)

30(60.0)

190(95.0)

 Yes

20(40.0)

3(2.0)

20(40.0)

10(5.0)

Do you hav&e chronic diarrhea?

0.062

0.180

 No

48(96.0)

150(100.0)

48(96.0)

198(99.0)

 Yes

2(4.0)

0(0.0)

2(4.0)

2(1.0)

Do you have urethritis ?

 < 0.001

 < 0.001

 No

41(82.0)

150(100.0)

41(82.0)

199(99.5)

 Yes

9(18.0)

0(0.0)

9(18.0)

1(0.5)

Do you have psoriasis ?

0.250

0.200

 No

49(98.0)

150(100.0)

49(98.0)

200(100.0)

 Yes

1(2.0)

0(0.0)

1(2.0)

0(0.0)

Does one of your family members have AS?

-

0.800

 No

50(100.0)

150(100.0)

50(100.0)

199(99.5)

 Yes

0(0.0)

0(0.0)

0(0.0)

1(0.5)

Does one of your family members have psoriasis/uveitis/ chronic diarrhea?

-

0.800

 No

50(100.0)

150(100.0)

50(100.0)

199(99.5)

 Yes

0(0.0)

0(0.0)

0(0.0)

1(0.5)

Do you have nodules ?

0.750

0.407

 No

50(100.0)

149(99.3)

50(100.0)

196(98.0)

 Yes

0(0.0)

1(0.7)

0(0.0)

4(2.0)

Do you have dactylitis ?

0.014

0.016

 No

46(92.0)

149(99.3)

46(92.0)

198(99.0)

 Yes

4(8.0)

1(0.7)

4(8.0)

2(1.0)