Table 1 Baseline characteristics of the study population (N = 4,843).

From: Urine 6-Bromotryptophan: Associations with Genetic Variants and Incident End-Stage Kidney Disease

Characteristic

Overall

Category of urine 6-bromotryoptophana

Undetectable

Low

High

P-valueb

N

4843

2068

1392

1383

 

6-bromotryptophan, mean (SD)

0.96 (0.56)

NA

0.55 (0.17)

1.37 (0.51)

 

Leading CKD cause acc. to treating nephrologist, % (n)c

    

0.001

Vascular nephropathy

23 (1107)

21 (443)

23 (321)

25 (343)

 

Primary glomerulopathy

19 (912)

18 (381)

19 (268)

19 (263)

 

Diabetic nephropathy

15 (704)

16 (340)

16 (217)

11 (147)

 

Systemic disease

8 (387)

8 (175)

7 (102)

8 (110)

 

Male sex, % (n)

60 (2917)

54 (1108)

61 (856)

69 (953)

<0.001

Age, years, mean (SD)

60.1 (12)

60.6 (11.42)

60.5 (11.89)

58.8 (12.85)

0.001

Smoking, % (n)

    

<0.001

Non-smoker

41 (1967)

39 (805)

40 (558)

44 (604)

 

Former smoker

43 (2102)

44 (900)

43 (597)

44 (605)

 

Current smoker

16 (774)

18 (363)

17 (237)

13 (174)

 

Education, % (n)

    

0.020

Higher

17 (806)

15 (314)

17 (240)

18 (252)

 

Middle

28 (1343)

27 (551)

28 (396)

29 (396)

 

Lower

54 (2595)

56 (1168)

52 (726)

51 (701)

 

Other

2 (99)

2 (35)

2 (30)

2 (34)

 

Body mass index, kg/m², mean (SD)d

29.8 (5.9)

29.7 (6.03)

29.7 (5.8)

29.9 (5.82)

0.718

Waist-to-hip ratio, median (IQR)

0.94 (0.88–1)

0.93 (0.87–0.99)

0.94 (0.89–1)

0.95 (0.89–1.01)

<0.001

Blood pressure, systolic, mmHg, mean (SD)

139.4 (20.3)

138.6 (20.91)

139.1 (20.02)

140.9 (19.59)

0.006

Blood pressure, diastolic, mmHg, mean (SD)

79.3 (11.74)

77.8 (11.76)

79.1 (11.49)

81.7 (11.59)

<0.001

Diabetes mellitus, % (n)

35 (1705)

40 (826)

36 (505)

27 (374)

<0.001

Hypertension, % (n)

96 (4664)

97 (2012)

97 (1353)

94 (1299)

<0.001

Coronary heart disease, % (n)

20 (967)

23 (469)

19 (258)

17 (240)

<0.001

Serum albumin, g/dL, mean (SD)d

3.84 (0.44)

3.83 (0.44)

3.81 (0.49)

3.87 (0.40)

0.009

Serum C-reactive protein, mg/L, median (IQR)

2.3 (1.01–4.92)

2.2 (1–4.81)

2.3 (0.98–4.94)

2.3 (1.06–5.1)

0.398

HDL-C, mg/dL, mean (SD)

52 (18.14)

53.4 (19.64)

51.6 (17.07)

50.2 (16.63)

<0.001

LDL-C, mg/dL, mean (SD)

118.3 (43.51)

116.2 (43.47)

119.8 (45.69)

119.7 (41.18)

<0.001

Serum triglycerides, mg/dL, median (IQR)d

167.9 (117.54–238.76)

167.6 (116.02–250.66)

170.7 (119.04–235.96)

164.2 (117.64–230.51)

0.226

eGFR, mL/min/1.73 m², mean (SD)

49.4 (18.24)

45 (16.53)

48.7 (16.83)

56.7 (19.71)

<0.001

UACR, mg/g, median (IQR)

50.5 (9.55–384.17)

58.1 (12.26–498.97)

53.3 (8.71–405.42)

37.2 (6.6–265.69)

<0.001

Blood pressure medication: by renin-angiotensin system, % (n)

81 (3924)

82 (1701)

83 (1152)

77 (1071)

<0.001

* ACE inhibitors

47 (2292)

48 (983)

49 (680)

45 (629)

 

* ARB

42 (2021)

44 (919)

42 (582)

38 (520)

 

* ACE and ARB

8 (389)

10 (201)

8 (110)

6 (78)

 

* ACE or ARB

73 (3535)

73 (1500)

75 (1042)

72 (993)

 

Diuretic use, % (n)

60 (2926)

71 (1466)

58 (813)

47 (647)

<0.001

* Potassium-sparing

10 (477)

11 (228)

10 (134)

8 (115)

 

* Thiazide

26 (1281)

26 (533)

29 (407)

25 (341)

 

* Aldosterone antagonist

8 (383)

9 (194)

8 (106)

6 (83)

 

* Loop diuretics

38 (1838)

54 (1122)

30 (421)

21 (295)

 

Death event, % (n)e

7 (325)

8 (167)

6 (78)

6 (80)

 

Major causes of death, % (n)f

     

Due to forgoing of dialysis

0 (9)

0 (4)

0 (2)

0 (3)

 

Cardiovascular disease

(e.g. myocardial infarction)

2 (108)

3 (60)

2 (25)

2 (23)

 

Cerebrovascular disease

(e.g. stroke)

0 (14)

0 (6)

0 (4)

0 (4)

 

Infection

1 (64)

2 (39)

1 (11)

1 (14)

 

ESKD event, % (n)e

4 (216)

6 (127)

4(55)

2 (34)

 
  1. Abbreviations. HDL-C, high density lipoprotein cholesterol; LDL-C, low density lipoprotein cholesterol; eGFR, estimated glomerular filtration rate; UACR, urine albumin-to-creatinine ratio; ACE, angiotensin converting enzyme; ARB, angiotensin receptor blocker; ESKD, end-stage kidney disease; IQR, interquartile range (25th and 75th percentiles); * Subcategories; aSubcategories according to levels of urine 6-bromotryptophan: undetectable levels; low, range: 0.135 to < 0.84 (median); high, range: 0.84 (median) to 5.31; bStatistical comparison of groups for categorical variables (Pearson’s Chi-squared test) and for continuous variables (Kruskal-Wallis rank sum test); cMajor leading causes of CKD as reported by the treating nephrologist (N > 300); dVariables with missing values: body mass index N = 41, serum albumin N = 1, serum triglycerides N = 2 (overall < 1%); eFollow-up time was restricted to the period from study entry to 1,500 days (4.11 years); fCauses of death with at least 50 events, except for death due to forgoing of dialysis.
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