title: A method for estimating within-patient variability in maximal urinary flow rate adjusted for voided volume.
abstract: OBJECTIVE
  To investigate whether volume adjustment can be used to reduce the within-patient variability of the maximal urinary flow rate (Qmax) without affecting the variability between patients.
  
  
  METHODS
  We analyzed 2049 urinary flow curves of 208 men with lower urinary tract symptoms suggestive of bladder outlet obstruction and studied the relation between Qmax and voided volume (VV) in individual patients using multilevel regression analysis.
  
  
  RESULTS
  In agreement with most previous studies, we found a hyperbolic relation between the VV and Qmax. Although hyperbolic on average, the slope of the regression line relating the VV to Qmax differed substantially across individual patients. In some patients, Qmax even tended to be lower with an increased VV.
  
  
  CONCLUSIONS
  The reproducibility of Qmax is poor, in part because of its dependence on the VV. The current methods to adjust Qmax for VV, such as the Siroky nomogram, minimize between-patient dependency, whereas our findings emphasize the importance of within-patient variability. A common approach to adjust Qmax for VV, however, is not feasible, because the relation of Qmax to VV differs substantially across patients. The only valid, although impractical option, remains to record a large number of urinary flow curves for each patient.
authors.affiliation: Department of Urology, University Medical Center, Nijmegen, The, Nijmegen, Netherlands.
authors.forename: Gabe S
authors.initials: GS
authors.lastname: Sonke
authors.forename: Chris
authors.initials: C
authors.lastname: Robertson
authors.forename: André L M
authors.initials: AL
authors.lastname: Verbeek
authors.forename: Wim P J
authors.initials: WP
authors.lastname: Witjes
authors.forename: Jean J M C H
authors.initials: JJ
authors.lastname: de la Rosette
authors.forename: Lambertus A
authors.initials: LA
authors.lastname: Kiemeney
mesh_terms: D003950:Diagnostic Techniques, Urological / Q000592:standards*; D006801:Humans; D008297:Male; D012044:Regression Analysis; D015203:Reproducibility of Results; D014563:Urodynamics / Q000502:physiology*; D014570:Urologic Diseases / Q000503:physiopathology