title: Thresholds for significant decrease in hemodialysis access blood flow.
abstract: During hemodialysis access surveillance, referral for evaluation and correction of stenosis is based upon determination that a significant decrease in blood flow (Q) has occurred. However, criteria for determining when a decrease is statistically significant have not yet been established. In this study we established such criteria by analyzing Q variation with the glucose pump test (GPT). We took nine Q measurements in each of 25 patients (18 grafts, 7 fistulas) during three dialysis sessions within a 2-week period (predialysis and during hours 1 and 3). We determined thresholds that define a significant percentage decrease in Q (deltaQ) for various p values. In order to confirm the general applicability of these thresholds, we computed the average within-patient Q variation during the three sessions (computed as a coefficient of variation and referred to as short-term variation). We then determined the relative influences of biological (true) variation and analytical error on short-term variation. We found that deltaQ must be > 33% to be significant at p < 0.05, whereas the threshold is > 17% for p < 0.20. Measuring Q at uniform versus different times during the sessions did not significantly reduce these thresholds. We also found that biological variation was nearly as large as short-term Q variation, whereas analytical error contributed minimally to short-term variation. In conclusion, this study defines thresholds for a significant deltaQ that have wide application in determining access referral for evaluation and correction of stenosis. Selection of a particular threshold should consider the relative importance of avoiding thrombosis versus avoiding unnecessary procedures. If avoiding unnecessary procedures is a priority, then we recommend a threshold of > 33%. These thresholds apply to other methods of measuring Q, provided analytical error is significantly less than biological variation.
authors.affiliation: Division of Nephrology and Hypertension, Department of Medicine, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.
authors.forename: Sunanda J
authors.initials: SJ
authors.lastname: Ram
authors.forename: Raja
authors.initials: R
authors.lastname: Nassar
authors.forename: Rashid
authors.initials: R
authors.lastname: Sharaf
authors.forename: Alberto
authors.initials: A
authors.lastname: Magnasco
authors.forename: Steven A
authors.initials: SA
authors.lastname: Jones
authors.forename: William D
authors.initials: WD
authors.lastname: Paulson
mesh_terms: D001166:Arteriovenous Shunt, Surgical; D001783:Blood Flow Velocity; D001786:Blood Glucose / Q000032:analysis; D001795:Blood Pressure Determination; D005260:Female; D006083:Graft Occlusion, Vascular / Q000097:blood / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D011138:Polytetrafluoroethylene; D006435:Renal Dialysis
chemical_list: D001786:Blood Glucose; D011138:Polytetrafluoroethylene