|Year : 2019 | Volume
| Issue : 1 | Page : 345-351
Plasma levels of von Willebrand factor in maintenance hemodialysis patients: its relation to vascular access thrombosis
Hassan Abd El-Hady1, Mahmoud A Kora1, Khaled M. A. El-Zorkany1, Belal A Montaser2, Amira M. E. Yousuf3
1 Department of Internal Medicine, Faculty of Medicine, Menoufia University, Shebeen El-Kom, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Menoufia University, Shebeen El-Kom, Egypt
3 Department of Nephrology, Benha Teaching Hospital, Banha, Egypt
|Date of Submission||25-Jun-2017|
|Date of Acceptance||13-Aug-2017|
|Date of Web Publication||17-Apr-2019|
Amira M. E. Yousuf
Shebeen El-Kom, Menoufia, 32511
Source of Support: None, Conflict of Interest: None
The aim of this study was to assess von Willebrand factor (VWF) plasma levels in patients under maintenance hemodialysis (HD) to determine its role in the occurrence of vascular access thrombosis (VAT) in such patients.
HD process is associated with increasing thrombotic trend especially owing to platelets and clotting factor activation. Vascular access complications increase morbidity and contribute to 20–25% of all hospitalizations in HD patients, of which ~ 85% of these cases are because of thrombosis. VWF is an important component of the hemostatic system and a hypercoagulability state biomarker.
Patients and methods
This case–control study was conducted on 60 patients on HD for more than 6 months classified into two groups: group I (GI) included 30 patients with VAT, whereas group II (GII) included 30 patients without VAT. Moreover, 20 healthy individuals served as a control group. History taking, clinical examination, and investigations (complete blood count, kidney function tests, liver function tests, lipid profile, fasting blood sugar, postprandial blood sugar, and serum VWF) for all cases were done.
Mean VWF serum level was found to be higher in HD groups (GI 1361.47 ± 270.38 and GII 950 ± 138.12) than control group (351.5 ± 34.8), with highly statistical significance. A cutoff level of VWF at 1277 ng/ml is accurate (46.67%) for ocurrance of VAT in GI patients, with sensitivity of 93.33%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93.8%.
High VWF levels related to development of VAT.
Keywords: hemodialysis, vascular access thrombosis, von Willebrand factor
|How to cite this article:|
El-Hady HA, Kora MA, El-Zorkany KM, Montaser BA, Yousuf AM. Plasma levels of von Willebrand factor in maintenance hemodialysis patients: its relation to vascular access thrombosis. Menoufia Med J 2019;32:345-51
|How to cite this URL:|
El-Hady HA, Kora MA, El-Zorkany KM, Montaser BA, Yousuf AM. Plasma levels of von Willebrand factor in maintenance hemodialysis patients: its relation to vascular access thrombosis. Menoufia Med J [serial online] 2019 [cited 2019 Aug 25];32:345-51. Available from: http://www.mmj.eg.net/text.asp?2019/32/1/345/256111
| Introduction|| |
Hemodialysis (HD) process is associated with increasing thrombotic trend especially owing to platelets and clotting factors activation . Thrombotic episodes in HD patients are mainly related to a reduction in vascular access blood flow owing to fibromuscular and intimal hyperplasia, which may result in vascular access stenosis. The blood flow reduction causes blood stasis and favors hypercoagulability, hypotension, and hypovolemia, predisposing to a prothrombotic environment .
Von Willebrand factor (VWF) is an important component of the hemostatic system and a hypercoagulability state biomarker . The VWF is a multimeric glycoprotein composed of identical subunits of 270 kDa each containing 2050 amino acids synthesized by endothelial cells and megakaryocytes. The synthesis occurs initially in the endoplasmic reticulum, where there is the formation of pre-VWF dimers linked at the carboxy terminal disulfide.
These predimers migrate to the Golgi complex, where other disulfide bonds at the amino terminus link two dimmers together to form multimers resulting in ultralarge multimers of the VWF, which are stored in endothelial cells and platelets. VWF dimers are secreted into the plasma and the subendothelium, whereas ultralarge VWF are stored within the Weibel–Palade bodies of endothelial cells and their release to plasma is limited to sites of endothelial damage . VWF directly contributes to thrombus formation by mediating platelet adhesion to subendothelial collagen and, indirectly, by being the carrier of FVIII and by preventing its plasmatic clearance . Several clinical conditions are associated with increase of VWF secretion by endothelium, contributing to thrombus formation. This may explain the association of elevated levels of FVIII and VWF with thromboembolism, atherosclerosis, and preeclampsia .
Although it is still not clear the mechanism that results in the imbalance of VWF plasma levels in HD patients, this probably contributes to the hypercoagulability state seen in these patients, who have increased risk of thrombosis .
The aim of this study was to assess VWF plasma levels in patients under maintenance HD to determine its role in the occurrence of vascular access thrombosis (VAT) in such patients.
| Patients and Methods|| |
This case–control study was conducted on 60 patients with end-stage renal disease (ESRD) under regular HD for more than 6 months in Hemodialysis Units of Benha and Shebeen El-Kom Teaching Hospitals, Egypt, and 20 healthy individuals who served as a control, during the period from August 2015 to April 2016. An informed consent was taken from all included participants and from the medical ethical committee of the hospitals.
Patients were classified into three groups:
Group I (GI) included 30 (15 males and 15 females) patients with ESRD on regular HD with VAT, which was defined by the absence of blood flow and the impossibility to use the access for dialysis. Group II (GII) included 30 (15 males and 15 females) patients with ESRD on regular HD without VAT. Group III included 20 healthy participants who were clinically free and volunteered to participate in the study.
The inclusion criteria were adult patients with end-stage renal disease on maintenance HD. Exclusion criteria were patients with CKD stages (1–4), acute infection, connective tissue disease, malignancy, chronic liver disease, thyroid gland dysfunction, recent myocardial infarction, recent trauma, and oral anticoagulants.
Careful history was taken including personal history, present history specifically stressing (for patients) on the duration of hd treatment, type of vascular access, dry body weight and average weight gain between dialysis sessions, other organ dysfunctions, drug history, and history of occurance of vat or other thrombotic events. in addition, complete general and local examination was done with special emphasis on examination of vascular access: inspection – examination of the site of the arteriovenous (av) access, the remaining part of arm, shoulder, breast, neck, and face. palpation and auscultation – pulse: normally, an av access demonstrates a soft pulse that is easily compressed by the application of gentle pressure. thrill – the thrill of an av access is a 'buzz' that can be felt by the examining fingers. the thrill can be continuous or discontinuous. normally, there is a continuous nature to the thrill except at the arterial anastomosis where the thrill normally is discontinuous. auscultation – it is performed to assess the quality of the bruit in the av access) .
Routine investigation included complete blood count; kidney function comprising blood urea, serum creatinine, and serum uric acid; urea reduction ratio; Kt/V; estimated glomerular filtration rate by MDRD equation; liver function test using bilirubin; transaminases (aspartate transaminase and alanine transaminase); alkaline phosphatase; serum albumin; prothrombin time (PT); lipid profile using total cholesterol, triglyceride (TG), low-density lipoprotein (LDL), and high-density lipoprotein (HDL); blood sugar using fasting blood sugar (FBS) and 2 h postprandial blood sugar; and pelvic-abdominal ultrasound).
Measurement of serum VWF using VWF antigen was performed by enzyme-linked immunosorbent assay, using the VWF Kit IMUBIND (WKEA Med Supplies Corp., California, USA) for all patients and controls.
Blood samples were collected under aseptic conditions from HD vascular access before dialysis procedure at the first dialysis session of the week and before heparin administration.
Overall, 4 ml of blood was delivered in a plastic tube with EDTA (catalogue no. 367654; Becton Dickinson, San Jose, CA, USA) for complete blood count.
Another 4 ml of blood was collected in a clean dry tube.
Blood was left to clot at 37°C. Serum was then separated after centrifugation at 3000 rpm for 10 min and kept for biochemical analysis (kidney and liver functions, blood sugar, and lipid profile).
Serum VWF levels were determined for all patients and controls by using validated enzyme-linked immunosorbent assay method via the VWF Kit IMUBIND (WKEA Med Supplies Corp.).
Overall, 4 ml of blood was collected in a clean dry tube. Plasma was collected using one-tenth volume of 0.1 mol/l sodium citrate as an anticoagulant. Blood samples from healthy volunteers were collected from arm veins in sodium citrate and processed in the same way as described before.
Normal human plasma VWF concentration has been reported ranging approximately from 0.3 to 1.57 IU/ml .
All data were collected, tabulated, and statistically analyzed using personal computer using Stata/SE, version 11.2 for Windows (Stata Corporation, College Station, Texas, USA).
The collected data were summarized in terms of mean ± SD and range for quantitative data and frequency and percentage for qualitative data. Comparisons between different study groups using the χ2-test and Fisher exact test were done to compare proportions as appropriate. Pearson's correlation coefficient (r) and Spearman's correlation coefficient (ρ) were used to test for the correlation between VWF and estimated parameters as appropriate. Receiver operating characteristics analysis was carried out to evaluate the diagnostic performance of VWF levels for VAT screening among studied patients. Stepwise logistic regression analysis for VAT in studied patients conditioned on VWF, potential risk factors, and laboratory data was carried out to detect important predictors of VAT, and the results were presented as odds ratio and 95% confidence interval. After the calculation of each of the test statistics, the corresponding distribution tables were consulted to get the P value [Figure 1].
|Figure 1: Receiver operating characteristics (ROC) analysis of the von Willebrand factor for the prediction of vascular access thrombosis in group I patients.|
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| Results|| |
This study included three groups. The first group consisted of 30 patients on HD with VAT, whose mean age was 53.73 ± 8.07 years and had been on dialysis for different years, with mean of 5.97 ± 2.02 (range: 2–11 years). The second group consisted of 30 patients on HD without VAT, whose mean age was 46.07 ± 8.11 years and had been on dialysis for different years, with mean of 4.83 ± 1.44 (range: 3–9 years). All HD patients underwent dialysis three times per week with different duration of each session ranging from 3 to 4 h. Finally, the control group represented 20 healthy individuals, with mean age of 42.45 ± 5.44 years. The difference between groups was significant regarding age (P < 0.001), dialysis duration (P = 0.01), and blood pressure (P = 0.004). The mean systolic blood pressure was higher in HD groups (GI 130.67 ± 12.01 and GII 122 ± 10.63). Regarding laboratory characteristics, the results indicated that there is significant difference regarding mean LDL (mg/dl) (Z = 3.53, P < 0.001); mean cholesterol (mg/dl) (f = 7.95, P < 0.001); 2 h postprandial (PP) (mg/dl) (Z = 2.71, P = 0.007); FBS (mg/dl) (t = 2.38, P = 0.02); TGs (mg/dl) (t = 2.07, P = 0.04), which were higher in GI; and blood urea (mg/dl) (t = 2.72, P = 0.009), which was higher in GII. There is no significant difference regarding Kt/V, urea reduction ratio, estimated glomerular filtration rate, hemoglobin, serum creatinine, HDL, serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase, albumin, and PT [Table 1].
|Table 1: Clinical and laboratory characteristics of the studied patients|
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There was highly significant increase in VWF levels in patients in GI and GII compared with controls (GIII) (P < 0.001) [Table 2].
VWF in studied patients according to type of vascular access showed a highly significant increase in GI patients with VAT compared with GII patients (ng/ml) (t = 7.23, P < 0.001) [Table 3].
|Table 3: Von Willebrand factor in studied groups according to type of vascular access|
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VWF in G1 according to frequency of VAT showed significant increase in patients with frequent thrombosis of three times per week (P = 0.04) [Table 4].
|Table 4: Von Willebrand factor in group 1 according to frequency of vascular access thrombosis|
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The correlation coefficient (r) between serum VWF and clinical and laboratory data of the studied patient groups showed significant negative correlation in GI regarding predialysis SBP (mmHg) (r=−0.42, P = 0.02) and SGOT (U/l) (r=−0.41, P = 0.02), significant positive correlation in GI regarding blood urea (mg/dl) (r = 0.39, P = 0.03) and HDL (mg/dl) (ρ = 0.48, P = 0.007), significant positive correlation in GII withLDL (mg/dl) (ρ = 0.36, P = 0.047), and significant negative correlation in GII with PT (s) (r = −0.45, P = 0.01). No significant correlation in GI and GII regarding age, HD duration, predialysis diastolic blood pressure, hemoglobin, serum creatinine, LDL, cholesterol, TGs, serum glutamic pyruvic transaminase, and albumin [Table 5].
|Table 5: Correlation coefficient (r) between serum von Willebrand factor and clinical and laboratory data of the studied patient's groups|
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Logistic regression analysis for prediction of VAT in G1 patients showed that VWF and TGs each were significant independent factors (P = 0.001 and 0.03, respectively) for detection of VAT in studied patients [Table 6].
|Table 6: Logistic regression analysis for prediction of independent factor of vascular access thrombosis in studied patients|
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The cutoff level of VWF at 1277 ng/ml is accurate (96.67%) for occurrence of VAT in GI patients, with sensitivity of 93.33%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93.8% [Table 7].
|Table 7: Accuracy of von Willebrand factor for occurance of vascular access thrombosis in group I patients|
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| Discussion|| |
Vascular access complications increase morbidity and contribute to 20–25% of all hospitalizations in HD patients, of which ~85% of these cases are because of thrombosis. Therefore, it is extremely relevant to fully understand the factors that synergizes with this hypercoagulability state in HD patients for thrombus formation .
In the present study, the difference between studied groups was significant regarding age and dialysis duration (P < 0.001 and P = 0.01, respectively).
Increasing the mean age of patients with ESRD reflects the improvement of health care; however, we are still away from the developed countries, as mean age in USA was 61.1 years  and in UK was 65.9 years .
There was significant difference between patients regarding systolic blood pressure (P = 0.004); the mean systolic blood pressure was higher in HD groups (GI 130.67 ± 12.01 mm Hg and GII 122 ± 10.63 mmHg). This result matched with Salem , who found that 72% of HD patients have elevated blood pressure.
Studies by El-Wakil et al. , El-Shehaby et al. , and USRDS  found that hypertension was present in most of patients with ESRD explained by the fact that there is a strong relationship between hypertension and ESRD.
The mean blood urea levels were significantly higher in our HD patients (GI 134.23 ± 15.36 mg/dl and GII 150.97 ± 30.00 mg/dl), with P = 0.009. The study by Amin et al.  also detected that predialysis serum urea level was significantly higher than normal range (20–40 mg/dl). Most of the patients (53%) had serum urea level between 200 and 300 mg/dl.
In the current study, we noticed significant difference regarding blood sugar (P values in FBS and 2 h PP were 0.02 and 0.007, respectively).
Lipid profile in studied dialysis patients showed significant higher serum cholesterol, TGs, and LDL in GI than GII patients.
In a study by De Marchi et al.  for comparison between patients with and without fistula dysfunction showed that patients who experienced fistula dysfunction had a more severe hyperlipidemia as indicated by higher values of cholesterol and TGs and lower values of HDL.
A newer study by Abumwais and Idris  showed that HD patients have a statistically significant higher TGs and very LDL levels and low HDL levels compared with normal healthy controls. There were no statistically significant differences in total cholesterol or LDL levels.
Maheshwari et al.  reported that the serum TG levels were found to be significantly higher in HD patients as compared with control group, whereas HDL was found to be low in HD patients. Total cholesterol, LDL, very LDL, and chylomicrons were not significantly different between the patient and control groups.
VWF in the studied patients and controls showed highly significant increase of VWF levels in GI and GII patients compared with controls (P < 0.001).
VWF in studied patients according to type of vascular access showed a highly significant increase in GI patients with VAT compared with GII patients (P < 0.001). VWF in GI according to frequency of VAT showed significant increase in patients with frequent thrombosis of three times per week (P = 0.04).
Previous studies also detected elevated levels of VWF antigen in HD patients, but there was difference in the relation between this elevation and development of VAT.
Same finding was observed in a study by Sioulis et al.  which reported that patients with ESRD receiving HD treatment have elevated levels of VWF. In the study, VWF levels were significantly higher in HD patients compared with control group. Of equal importance was the observation that patients presenting thrombotic complications during the period of follow-up had significantly elevated VWF levels compared with HD patients who did not present any thrombotic complication.
A study by Rios et al.  showed that the levels of VWF were increased in HD patients, as compared with healthy control patients. However, no significant differences were detected in levels of this marker, comparing patients with and without VAT, suggesting that HD triggers a hypercoagulability state, regardless of the development of VAT.
Rios et al.  have mentioned higher FVIII activity and VWF plasma levels in HD patients compared with healthy patients, showing that these patients are at risk of thrombotic events.
In the present study, a significant positive correlation was found between serum VWF, blood urea (P = 0.03), and HDL (P = 0.007) in GI; significant negative correlation with predialysis SBP (mmHg) in GI (P = 0.02) and SGOT (U/l) (P = 0.02), significant positive correlation in GII withLDL (mg/dl) (P = 0.047), and significant negative correlation in GII with PT (s) (P = 0.01).
Sioulis et al.  showed that age and elevated levels of VWF were found to be the only factors related to the thrombotic episodes, shown in 20 patients of this study.
In our study, logistic regression analysis was performed to determine the independent factor of VAT in HD patients and found that VWF and TGs (mg/dl) were significantly correlated with occurance of VAT in studied patients (P = 0.001 and 0.03, respectively).
Malyszko and Mysliwviec  showed that elevated levels of VWF, in combination with other independent risk factors, as hypertension, diabetes, age, smoking, HD duration, and type of heparin used seem to contribute in the appearance of thrombotic events.
Borawski et al.  reported on logistic regression that elevated VWF Ag level was directly associated with use of enoxaparin. On linear regression analysis, VWF Ag correlated positively with age and fibrinogen and inversely with albumin and predialysis blood pressure.
For detecting the accuracy of VWF in occurance of VAT in GI patients of the current study, it was noticed that the optimal cutoff point of VWF at 1277 ng/ml is accurate (96.67%) for ocurrance of VAT in GI patients with sensitivity of 93.33%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93.8%.
| Conclusion|| |
VWF is elevated in the studied HD patients with VAT, and its diagnostic accuracy is 96.67% for the presence of VAT at a cutoff level 1277 ng/ml, with 100% specificity and 93.33% sensitivity.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]