PLATELET LEUKOCYTE AGGREGATES AS A PRO-THROMBOTIC RISK FACTOR IN PATIENTS WITH INFLAMMATORY BOWEL DISEASE

Document Type : Original Article

Authors

1 Department of Internal Medicine, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

2 Department of Clinical Pathology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Abstract

Background: Patients with inflammatory bowel disease (IBD) are at an increased risk for venous thromboembolism (VTE). VTE events carry significant morbidity and mortality, and have been associated with worse outcomes in patients with IBD. Studies have suggested that the hypercoagulable nature of the disease stems from a complex interplay of systems that include the coagulation cascade, endothelium, immune system, and platelets. Additionally, clinical factors that increase the likelihood of a VTE event among IBD patients include pregnancy, active disease, more extensive disease, hospitalization, and IBD-related surgeries.
Objective: To assess the platelet-leukocyte aggregation in patients with IBD and its relation to disease activity.
Patients and Methods: This was a prospective cohort study conducted on 40 IBD Patients and 20 control cases who were admitted to Al-Hussein University Hospital, and some selected from outpatient clinic, during the period from 15th of April, 2020 to 31st of March, 2021. All participants underwent to clinical examination, laboratory findings, colonoscopy, histopathology and flowcytometric findings were recorded from patients.
Results: There was a statistical significant difference (p-value < 0.001) between studied groups as regard hemoglobin level, white blood cells and platelets count. Statistical significant difference (p-value < 0.05) was found between studied groups as regard erythrocytic sedimentation rate and statistical significant difference (p-value < 0.001) between studied groups as regard C reactive protein and Fecal calprotectin. Also, there was a statistical significant difference (p-value < 0.001) between studied groups as regard ulcer, ileitis and edematous mucosa. Statistical significant difference (p-value < 0.001) was found between studied groups as regard platelet leukocyte aggregates.
Conclusion: In patients with active inflammatory bowel disease (IBD), there was a significant high level of platelet leukocyte aggregates (PLAs), which might be explanation phenomena of increased risk for thrombosis.

Keywords

Main Subjects


PLATELET LEUKOCYTE AGGREGATES AS A PRO-THROMBOTIC RISK FACTOR IN PATIENTS WITH INFLAMMATORY BOWEL DISEASE

By

Ahmed Khalil Farag1, Mahmoud Abd El-Rashed Allam1, Ahmed Fathy Abd El-Azeez2 and Gamal Ali Badr1

Department of Internal Medicine1 and Clinical Pathology2, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Corresponding author: Ahmed Khalil Farag,

E-mail: akhalil2611687@gmail.com, Mobile: 01092931013

ABSTRACT

Background: Patients with inflammatory bowel disease (IBD) are at an increased risk for venous thromboembolism (VTE). VTE events carry significant morbidity and mortality, and have been associated with worse outcomes in patients with IBD. Studies have suggested that the hypercoagulable nature of the disease stems from a complex interplay of systems that include the coagulation cascade, endothelium, immune system, and platelets. Additionally, clinical factors that increase the likelihood of a VTE event among IBD patients include pregnancy, active disease, more extensive disease, hospitalization, and IBD-related surgeries.

Objective: To assess the platelet-leukocyte aggregation in patients with IBD and its relation to disease activity.

Patients and Methods: This was a prospective cohort study conducted on 40 IBD Patients and 20 control cases who were admitted to Al-Hussein University Hospital, and some selected from outpatient clinic, during the period from 15th of April, 2020 to 31st of March, 2021. All participants underwent to clinical examination, laboratory findings, colonoscopy, histopathology and flowcytometric findings were recorded from patients.

Results: There was a statistical significant difference (p-value < 0.001) between studied groups as regard hemoglobin level, white blood cells and platelets count. Statistical significant difference (p-value < 0.05) was found between studied groups as regard erythrocytic sedimentation rate and statistical significant difference (p-value < 0.001) between studied groups as regard C reactive protein and Fecal calprotectin. Also, there was a statistical significant difference (p-value < 0.001) between studied groups as regard ulcer, ileitis and edematous mucosa. Statistical significant difference (p-value < 0.001) was found between studied groups as regard platelet leukocyte aggregates.

Conclusion: In patients with active inflammatory bowel disease (IBD), there was a significant high level of platelet leukocyte aggregates (PLAs), which might be explanation phenomena of increased risk for thrombosis.

Keywords: IBD, PLAs, VTE.

 

 

INTRODUCTION

     Venous thromboembolism (VTE) is one of the well-studied extra intestinal manifestations of IBD, which includes deep vein thrombosis and pulmonary embolism. The higher risk of VTE in IBD patients is related to multiple factors. One major factor would be systemic inflammation, which causes a hypercoagulable state due to the activation of the coagulation cascade and platelet aggregation (Saibeni et al., 2010). IBD patients were found to have a 2- to 3-fold risk of VTE compared to non-IBD patients; increasing up to 8-fold during an IBD flares (Wallaert et al., 2012). VTE in IBD patients is associated with higher mortality, morbidity and in-hospital cost compared to non-IBD patients. Hospital stay and hospital charges were double in IBD patients who developed VTE compared to non-VTE IBD patients (Yuhara et al., 2013). Inflammatory bowel disease (IBD) is a chronic disease that affects the gastrointestinal tract and also has extra intestinal manifestations. IBD has 2 major disease entities: crohn’s disease (CD) and ulcerative colitis (UC) (Ananthakrishnan et al., 2018).

PATIENTS AND METHODS

     This prospective cohort study has been carried out at Al-Hussein University Hospital over a period of eleven months, from April-2020 to March 2021, and conducted on 40 IBD Patients and 20 control cases. Before starting the study, approval from the Ethics Committee, Faculty of Medicine, Al-Azhar University, Cairo, Egypt, was obtained. Additionally, an informed consent was obtained from every subject before recruitment for use of their medical reports. The inclusion criteria included, age range from 20-50 years, IBD patients confirmed with colonoscopy and histopathology. There were exclusion criteria that included patients with history suggesting hypercoagulable state, deep venous thrombosis (DVT). All patients were subjected to detailed medical history for name, age, sex, alcohol, occupational and drug history and history of other comorbid conditions), Laboratory investigations included complete blood count (CBC), liver function tests (alanine amino transferase (ALT), aspartate amino transferase (AST) and serum albumin), renal function tests (serum creatinine and blood urea), ESR, CRP, fecal calprotectin. Assesment of disease severity according to Montreal classification in ulcerative colitis and Chron´s disease activity index, colonoscopy and histopathology. Platelet leukocyte aggregates (by detecting cluster of differentiation (CD) 41 as a pan platelet marker and CD45 as a pan leukocyte marker by flowcytometry).

Statistical analyses: Data were analyzed using Statistical Package for the Social Science (SPSS) version 24.  Quantitative data were expressed as mean ± standard deviation (SD). Qualitative data were expressed as frequency and percentage.

The following tests were done:

•     Independent-samples t-test of significance was used when comparing between two means.

•     Mann Whitney U test was used when comparing between two means (for abnormal distributed data).

•     Chi-square test was used when comparing between non-parametric data.

•     A one-way analysis of variance (ANOVA) was used on comparing between more than two means.

•     Post Hoc test was used for multiple comparisons between different variables.

 


RESULTS

 

 

     Regarding description of demographic data, the median age of studied patients was 33.5 (28.3 – 40) and the median age of studied control cases was 33 (23.8 - 39.8). There were 18 diseased males (45%) and 22 diseased females (55%) and 12 control males (60%) and 8 control females (40%) in all studied patients. There were 4 diabetic (10%) and 5 hypertensive (13%) in studied patients and 1 diabetic (5%) and 2 hypertensive (10%) in control cases. There was no statistical significant difference (p-value > 0.05) between studied groups as regard age and sex, and no statistical significant difference (p-value > 0.05) between studied groups as regard to chronic diseases as diabetes mellitus (DM) and hypertension (HTN) (Table 1).


 

Table (1):  Comparison between studied groups as regard demographic data

Groups

Variables

Group A

(N = 40)

Group B

(N = 20)

P-value

Age (years)

Median

33.5

33

0.649

IQR

28.3 - 40

23.8 - 39.8

Sex

Male

18

45%

12

60%

0.273

Female

22

55%

8

40%

DM

No

36

90%

19

95%

0.509

Yes

4

10%

1

5%

HTN

No

35

88%

18

90%

0.776

 

Yes

5

13%

2

10%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     According to laboratory profiles, results showed that, the mean of all studied patients was 10 ± 1.6 (g/dl) regarding Hb level and the mean of all studied control cases was 12.5 ± 1.7 (g/dl). Also, results showed that WBCs, PLTs, ESR, CRP, fecal calprotectin, the median of all studied patients was 10.4 (8.7 - 12.9), 440 (362 - 493.8), 31 (18 – 50), 12 (6 – 15), 200 (120.5 - 357.5), respectively. Also, results showed that WBCs, PLTs, ESR, CRP, fecal calprotectin, the median of all studied control cases was 7.3 (5.5 - 8.9), 313.5 (235.8 - 345.8), 20 (15.3 - 30.8), 6 (4.25 - 8.75), 24.5 (15.3 - 35.3), respectively. There was a statistical significant difference (p-value < 0.001) between studied groups as regard Hb level, WBCs and PLTs count. Also there was a statistically significant difference (p-value < 0.05) between studied groups as regard ESR, and a statistical significant difference (p-value < 0.001) between studied groups as regard CRP and fecal calprotectin (Table 2).

 

 

Table (2):  Comparison between studied groups as regard to laboratory profile

Groups

Variables

Group A

(N = 40)

Group B

(N = 20)

P-value

Hb (g/dl)

Mean

10.0

12.5

< 0.001

±SD

1.6

1.7

WBCs (x 10³/mm³)

Median

10.4

7.3

< 0.001

IQR

8.7 - 12.9

5.5 - 8.9

PLTs (x 10³/mm³)

Median

440

313.5

< 0.001

IQR

362 - 493.8

235.8 - 345.8

ESR (mm/h)

Median

31

20

< 0.002

IQR

18 - 50

15.3 - 30.8

CRP (mg/L)

Median

12

6

< 0.001

IQR

6 - 15

4.25 - 8.75

F.C.P

Median

200

24.5

< 0.001

IQR

120.5 - 357.5

15.3 - 35.3

 

 

     There was a statistical significant difference (p-value < 0.001) between studied groups as regard ulcer, ileitis and edematous mucosa. Also, there was no statistical significant difference (p-value > 0.05) between studied groups as regard mass, polyp and stricture (Table 3).

 

 

Table (3):  Comparison between studied groups as regard colonoscopy

Groups

Variables

Group A(N = 40)

Group B(N = 12)

P-value

Ileitis

No

12

30%

12

100%

< 0.001

Yes

28

70%

0

0%

Ulcer

No

9

22.5%

12

100%

< 0.001

Yes

31

77.5%

0

0%

Mass

No

39

97.5%

12

100%

0.51

Yes

1

2.5%

0

0%

Polyp

No

35

87.5%

12

100%

0.327

Yes

5

12.5%

0

0%

Edematus mucosa

No

14

35%

12

100%

< 0.001

Yes

26

65%

0

0%

Stricture

No

35

87.5%

12

100%

0.327

Yes

5

12.5%

0

0%

 

     Regarding platelet leukocyte aggregates, the mean of all patients was 3649±267.2, and the mean of all control cases was 519±43.1. There was a statistical significant difference between studied groups as regard PLAs (Table 4).

 

 

Table (4):  Comparison between studied groups as regard platelet leukocyte aggregates (PLAs)

Groups

Variables

Group A

(N = 40)

Group B

(N = 20)

P-value

PLAs

Mean

3649.0

519.0

< 0.001

±SD

267.2

43.1

 

 

     There was a statistical significant difference (p-value < 0.001) of platelet leukocyte aggregates (PLAs) as regard disease activity in group A (Activity assessed according to montreal classification in ulcerative colitis and Crohn’s disease activity index in C.D) (Table 5).

 

 

Table (5):  Comparison of platelet leukocyte aggregates (PLAs) as regard disease activity in patients (group A)

Activity in

group A

variables

Mild (N=40)

Moderate (N=40)

Severe

(N = 40)

C.R

(N = 20)

P-value

PLAs

Mean

3500.5

3673.4

3989.8

3422.0

< 0.001

±SD

258.2

179.9

39.5

133.9

 

 

     There was a statistically significant difference between mild active and moderate active patients of group A. Statistical significant difference between mild active and severe active patients of group A. No statistical significant difference between mild active and clinical remission patients of group A. Statistically significant difference between moderate active and severe active patients of group A. Statistically significant difference between moderate active and clinical remission patients of group A. Statistical significant difference between severe active and clinical remission patients of group A (Table 6)

 

 

Table (6):  Post-Hoc test for multiple comparisons between different activity categories as regard PLAs

 

LSD

p-value

Mild

Moderate

-172.9

0.024

Severe

-489.3

< 0.001

Clinical remission

78.5

0.438

Moderate

Mild

172.9

0.024

Severe

-316.4

0.001

Clinical remission

251.4

0.016

Severe

Mild

489.3

< 0.001

Moderate

316.4

0.001

Clinical remission

567.8

< 0.001

Clinical remission

Mild

-78.5

0.438

Moderate

-251.4

0.016

Severe

-567.8

< 0.001

 

 

DISCUSSION

     The results of current study showed a statistical significant difference between studied groups as regard Hb level, WBCs and Plt count. Also, results showed statistical significant difference between studied groups as regard ESR and statistical significant difference between studied groups as regard CRP and fecal calprotectin. In support to these results, Larsen et al. (2010) found that the thrombocytosis in colitis is also accompanied by significant leukocytosis which suggests that the responses may reflect enhanced hematopoiesis. Also, these results ran with Iskandar and Ciorba (2012) who found that WBCs may be an indicator of an exacerbation of inflammation in the course of UC. Also, ESR and CRP may be an indicator of an exacerbation of inflammation in the course of IBD. Also, these results ran with Matsuoka et al.(2018) who found that white blood cell count , platelet count, CRP and ESR are the most commonly used inflammatory indices in clinical practice for determining IBD activity. Also, Du et al. (2018) found that fecal biomarkers (including fecal calprotectin) reflect not only colonic disease but also the upper GIT and small bowel disease activity.

     The results of current study showed statistical significant difference between studied groups as regard ulcer, ileitis and edematous mucosa. These results ran with Weng et al. (2018) who found that 71% of UC patients with a VTE had pancolitis, and that all CD patients with a VTE had ileocolonic involvement.

     The results of current study showed a statistical significant difference between studied groups as regard PLAs.

Results showed statistical significant difference of PLAs as regard disease activity in all studied patients. PLAs were high in severe activity patients followed by moderate activity patients followed by mild activity patients and clinical remission patients. These results ran with Yoshida et al. (2010) who found that the more response of neutrophils in forming aggregates with platelets is consistent with neutrophil activation as an important component of the pathophysiology of IBD. Navaneethan et al. (2010) found that clinical evidence indicates that abnormalities in both coagulation and platelet function may account for the higher incidence of thromboembolic events detected in patients with IBD. Also, Schrottmaier et al. (2015) found that there were associations between PLAs and pro inflammatory effects in numerous pathological conditions, including cardiovascular disease, rheumatoid arthritis and inflammatory bowel disease.

CONCLUSION

     In patients with active inflammatory bowel disease (IBD), there were significant high levels of platelet leukocyte aggregates (PLAs) which might be an explanation phenomenon of increased risk for thrombosis.

REFERENCES

  1. Ananthakrishnan A. N., Bernstein C. N., Iliopoulos D., Macpherson  A., Neurath M. F., Ali R. A. R. and Fiocchi C. (2018): Environmental triggers in IBD: a review of progress and evidence. Nature Reviews Gastroenterology & Hepatology, 15(1), review of population-based studies. Lancet, 390: 2769-2778.
  2. Du L, Foshaug R, N. P., Scanu A. M. and Huang VW (2018): Within-stool and within day sample variability of fecal calprotectin in patients with inflammatory bowel disease: A prospective observational study. J Clin Gastroenterol., 52: 235– 40.
  3. Iskandar HB. and Ciorba MA (2012): Biomarkers in inflammatory bowel disease: current practices and recent advances. Transl Res., 159:313-325.
  4. Larsen S, Bendtzen K. and Nielsen OH. (2010): Extraintestinal manifestations of inflammatory bowel disease: epidemiology, diagnosis, and management. Ann Med., 42:97–114.
  5. Matsuoka K., Kobayashi T., Ueno F., Matsui T., Hirai F., Inoue N. and Kunisaki R. (2018): Evidence-based clinical practice guidelines for inflammatory bowel disease. Journal of Gastroenterology, 53(3), 305-353.
  6. Navaneethan U and Shen B (2010): Hepatopancreatobiliary manifestations and complications associated with inflammatory bowel disease. Inflamm Bowel Dis. Sep., 16(9):1598-619.
  7. Saibeni S, Saladino V, Sachar DB, Sands BE. and Chantarangkul V. (2010): Increased thrombin generation in inflammatory bowel diseases. Thromb Res., 125:278–282.
  8. Schrottmaier WC, Gerrits AJ, Flamini O, Pucciarelli S and Leven EA (2015): Aspirin and P2Y12 Inhibitors in plateletmediated activation of neutrophils and monocytes. Thromb Haemost., 114(3):478–489.
  9. Wallaert JB, De Martino RR, Marsicovetere PS, Laiakis E. C., Fornace A. J. and Amundson S. A (2012): Venous thromboembolism after surgery for inflammatory bowel disease: are there modifiable risk factors? Data from ACS NSQIP. Dis Colon Rectum., 55:1138–1144.
  10. Weng MT, Park SH, Matsuoka K, Tung CC, Lee JY, Chang CH, Yang SK, Watanabe M, Wong JM. and Wei SC. (2018): Incidence and Risk Factor Analysis of Thromboembolic Events in East Asian Patients With Inflammatory Bowel Disease, a Multinational Collaborative Study. Inflamm Bowel Dis., 24: 1791- 1800.
  11. Yoshida H, Russell J, Yilmaz CE, Granger DN and Senchenkova EY (2010): Interleukin-1beta mediates the extra-intestinal thrombosis associated with experimental colitis. Am J Pathol., 177:2774–2781.
  12. Yuhara H, Steinmaus C, Vakas M, Kolios G and Corley D. (2013): Meta-analysis:the risk of venous thromboembolism in patients with inflammatory bowel disease. Aliment Pharmacol Ther., 37:953–962.


تكتل كرات الدم البيضاء مع الصفائح الدموية كعامل خطورة للتجلط في مرضى القولون الإلتهابي

أحمد خليل فرج*، محمود عبدالرشيد علام*، أحمد فتحي عبدالعزيز**،

جمال علي بدر*

قسمى الأمراض الباطنة* والباثولوجيا الاكلينيكية**، كلية الطب، جامعة الأزهر

E-mail: akhalil2611687@gmail.com

خلفية البحث: المرضي الذين يعانون من مرض الأمعاء الملتهبة في خطر متزايد للتجلط الوريدي. وتحمل الأحداث الوريدية إعتلالاً ووفيات كبيرة، وارتبطت بنتائج أسوأ في المرضي الذين يعانون من مرض الأمعاء الملتهبة. وقد أشارت الدراسات الي أن طبيعة المرض القابله للتحلل الزائد تنبع من تفاعل معقد بين الانظمة التي تشمل تسلسل التخثر، والاندوثيليوم، والجهاز المناعي، والصفائح الدموية. وبالاضافة الي ذلك، فإن العوامل السريرية التي تزيد من إحتمالية حدوث التجلط الوريدي بين مرضى أمراض الأمعاء الالتهابية تشمل الحمل، والمرض النشط، والمرض الأكثر إتساعاً، والحجز بالمستشفي، والعمليات الجراحية المتصلة بالأمعاء الالتهابية.

الهدف من البحث: تقييم تكتل كرات الدم البيضاء مع الصفائح الدموية في المرضي الذين يعانون من مرض الأمعاء الملتهبة وعلاقته بنشاط المرض.

المرضى وطرق البحث: هذه دراسة جماعية أجريت على 40 حالة من مرضي الأمعاء الملتهبة بالإضافة إلى 20 حالة سليمة تم إدخالهم إلى مستشفى الحسين الجامعي، وبعضهم تم إختيارهم من العيادة الخارجية خلال الفترة من 15 أبريل 2020 إلى 31 مارس 2021. وسجلت من المرضى نتائج الفحص السريري، والنتائج المختبرية، والتنظير القولوني، والتنظير الهيستوباثولوجي، والقياس بجهاز فلوسيتوميتر.

نتائج البحث: كان هناك فارق كبير إحصائياً عالياً بين المجموعات المدروسة فيما يتعلق بنسبة الهيموجلوبين وعدد كرات الدم البيضاء والصفائح الدموية. وقد وجد فارق كبير إحصائياً بين المجموعات التي خضعت للدراسة فيما يتعلق بسرعة الترسيب. وهناك أيضاً فارق كبير إحصائياً بين المجموعات المدروسة فيما يتعلق بدلائل الإلتهابات ودلائل الإلتهاب البرازي. وقد وجد فارق كبير إحصائياً بين المجموعات المدروسة فيما يتعلق بمجموعات تكتل كرات الدم البيضاء مع الصفائح الدموية.

الاستنتاج: هناك مستويات عالية كبيرة من كرات الدم البيضاء المتكتله مع الصفائح الدموية في المرضى الذين يعانون من مرض الأمعاء الملتهبة النشطة والتي قد تكون بمثابة تفسير لظواهر زيادة خطر الإصابة بالتجلط.

الكلمات الدالة: مرض الأمعاء الملتهبة، تكتل كرات الدم البيضاء مع الصفائح الدموية، التجلط الوريدي.

  1. REFERENCES

    1. Ananthakrishnan A. N., Bernstein C. N., Iliopoulos D., Macpherson  A., Neurath M. F., Ali R. A. R. and Fiocchi C. (2018): Environmental triggers in IBD: a review of progress and evidence. Nature Reviews Gastroenterology & Hepatology, 15(1), review of population-based studies. Lancet, 390: 2769-2778.
    2. Du L, Foshaug R, N. P., Scanu A. M. and Huang VW (2018): Within-stool and within day sample variability of fecal calprotectin in patients with inflammatory bowel disease: A prospective observational study. J Clin Gastroenterol., 52: 235– 40.
    3. Iskandar HB. and Ciorba MA (2012): Biomarkers in inflammatory bowel disease: current practices and recent advances. Transl Res., 159:313-325.
    4. Larsen S, Bendtzen K. and Nielsen OH. (2010): Extraintestinal manifestations of inflammatory bowel disease: epidemiology, diagnosis, and management. Ann Med., 42:97–114.
    5. Matsuoka K., Kobayashi T., Ueno F., Matsui T., Hirai F., Inoue N. and Kunisaki R. (2018): Evidence-based clinical practice guidelines for inflammatory bowel disease. Journal of Gastroenterology, 53(3), 305-353.
    6. Navaneethan U and Shen B (2010): Hepatopancreatobiliary manifestations and complications associated with inflammatory bowel disease. Inflamm Bowel Dis. Sep., 16(9):1598-619.
    7. Saibeni S, Saladino V, Sachar DB, Sands BE. and Chantarangkul V. (2010): Increased thrombin generation in inflammatory bowel diseases. Thromb Res., 125:278–282.
    8. Schrottmaier WC, Gerrits AJ, Flamini O, Pucciarelli S and Leven EA (2015): Aspirin and P2Y12 Inhibitors in plateletmediated activation of neutrophils and monocytes. Thromb Haemost., 114(3):478–489.
    9. Wallaert JB, De Martino RR, Marsicovetere PS, Laiakis E. C., Fornace A. J. and Amundson S. A (2012): Venous thromboembolism after surgery for inflammatory bowel disease: are there modifiable risk factors? Data from ACS NSQIP. Dis Colon Rectum., 55:1138–1144.
    10. Weng MT, Park SH, Matsuoka K, Tung CC, Lee JY, Chang CH, Yang SK, Watanabe M, Wong JM. and Wei SC. (2018): Incidence and Risk Factor Analysis of Thromboembolic Events in East Asian Patients With Inflammatory Bowel Disease, a Multinational Collaborative Study. Inflamm Bowel Dis., 24: 1791- 1800.
    11. Yoshida H, Russell J, Yilmaz CE, Granger DN and Senchenkova EY (2010): Interleukin-1beta mediates the extra-intestinal thrombosis associated with experimental colitis. Am J Pathol., 177:2774–2781.
    12. Yuhara H, Steinmaus C, Vakas M, Kolios G and Corley D. (2013): Meta-analysis:the risk of venous thromboembolism in patients with inflammatory bowel disease. Aliment Pharmacol Ther., 37:953–962.