One hundred and fifteen HD patients provided written inform consent. 87 patients were excluded due to i) did not meet the criteria for AVF stenosis (n = 39), ii) used other vascular accesses (n = 48). The remaining 28 patients completed all baseline assessments and were enrolled in the study. Five patients were excluded due to not completed all vascular access measurements. Therefore, 23 patients were enrolled in the final analysis. (Fig. 1)
Twenty-three patients, who had clinical suspicion for AVF stenosis, were recruited. The characteristics of the patients and their AVFs are summarized in Table 1. The median time of dialysis duration was 5.5 years. Fourteen (60%) of the fistulas were located in the forearm (radiocephalic), and nine (40%) were located in the upper arm (brachiocephalic). Fifteen fistulas (65%) revealed physical signs suspicious for AVF stenosis. 35% of the patients showed significant increased venous pressure during dialysis time but could not detect by physical examination.
Table 1
Baseline demographic data.
Number of patients, n | 23 |
Sex male/female, n | 16/7 |
Age(years), mean (range) | 63.45 ( 46–80) |
Duration of HD (median years, range) | 5.5 (2–21) |
Underlying disease • Hypertension, n(%) • Coronary artery disease, n(%) • Diabetes, n(%) | 22 (95%) 13 (56.5%) 8 (34%) |
Caused of ESRD Diabetes, n (%) Hypertension, n (%) Glomerular diseases, n (%) Other, n (%) | 8 (34%) 7 (30.4%) 7 (30.4%) 1 (4.3%) |
Single pool Kt/V mean ± SD | 2.17 ± 0.50 |
Venous pressure (mmHg, mean ± SD) | 218 ± 20.49 |
The median access flows were 805, 828, and 604 mL/min by ultrasound dilution, urea dilution, and Doppler ultrasonography methods, respectively. Fistulography revealed AVF stenosis in eighteen patients, twelve of whom had significant stenosis (greater than 50%). The locations of the stenosis lesions were eight at the inflow site, six at the outflow site, and four patients had stenosis at both sites. The median access flows in the non-significant stenosis group and the significant stenosis group were shown in Table 2. In significant stenosis group, the ROC showed an area under the curve (AUC) of access flow was 0.53 (95% CI, 0.26 to 0.85) from ultrasound dilution, 0.63 (95% CI, 0.32 to 0.93) for urea dilution, and 0.93 (95% CI, 0.81 to 1.00) for Doppler ultrasound (Fig. 2). Doppler ultrasound is a highly accurate method for detection of AVF stenosis compared to the other non-invasive methods with statistical significance (P < 0.01 for both ultrasound dilution and urea dilution techniques). Sensitivity and specificity for detection of AVF stenosis by Doppler ultrasound were 80% and 100% (Table 3).
Table 2
Access flow measurement by non-invasive methods
Methods | Access flow (mL/min) (median with range) |
Ultrasound dilution | Urea dilution | Doppler ultrasound |
Non-significant Stenosis (≤ 50%) | 805 (748–1295) | 828 (575–1,267) | 604 (519–799) |
Significant stenosis (> 50%) | 625 (360–850) | 615 (385.32–966) | 590 (399–604) |
Table 3
Diagnostic performance of non-invasive methods for AVF stenosis
Methods | AUC | Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) |
Ultrasound dilution | 0.55 (95% CI,0.26–0.85) | 73 | 40 | 78 | 33 |
Urea dilution | 0.63 (95% CI, 0.32–0.93) | 73 | 80 | 92 | 57 |
Doppler ultrasound | 0.93 (95% CI, 0.81-1.00) | 80 | 100 | 100 | 80 |
At ROC curve analysis, the method with the best discriminatory capacity for diagnosis of non-significant AVF stenosis was Doppler ultrasound with an AUC of 0.93 (95% CI, 0.82 to 1.00).
The other methods demonstrated an AUC of 0.74 (95% CI, 0.52 to 0.97) for ultrasound dilution, and 0.82 (95% CI, 0.63 to 1.00) for urea dilution in detecting significant stenosis.
Doppler ultrasound is a high accuracy method for detection of AVF stenosis compared with other non-invasive methods with statistically significant (P < 0.01 for both ultrasound dilution and urea dilution). Sensitivity and specificity for the diagnosis of AVF stenosis more than 50% by Doppler ultrasound were 100%, and 82%, respectively. Sensitivity and specificity by other methods are shown in Table 4.
Table 4
Diagnostic performance of non-invasive methods for significant stenosis of AVF
Methods | AUC | Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) |
Ultrasound dilution | 0.74 (95% CI,0.52–0.97) | 89 | 46 | 57 | 83 |
Urea dilution | 0.82 (95% CI, 0.63-1.00) | 89 | 64 | 80 | 67 |
Doppler ultrasound | 0.93 (95% CI, 0.82-1.00) | 100 | 82 | 69 | 100 |
This study, physical examination had 80% sensitivity and 80% specificity for the diagnosis of AVF stenosis. Combining physical examination with non-invasive methods had improved their accuracy for diagnosis of AVF stenosis. The combinations of a positive physical examination with ultrasound dilution and urea dilution improved the sensitivity to 80% and 93%, respectively.
There were no differences between the two raters (Nephrologist and Radiologist) in terms of access flow measurement by Doppler ultrasound, the corresponding coefficient of variation (CV %) was 4.73, 4.53 respectively. However, for the dilution method, which was operated by hemodialysis staff nurses, we found %CV of 8%.