Rationalization of interpretation of uroflowmetry for a non-caucasian (Indian) population: conceptual development and validation of volume-normalized flow rate index.

Aims: We intended to define volume-normalized flow rates (cQ; VQI) and to construct and validate uroflow (Q)-volume (V) nomograms in our Indian (non-Caucasian) population.

Methods: Prospective observational study.

Participants: Group A, male healthy volunteers 18-45 years without LUTS. Group B, men >18 years with LUTS (IPSS > 7; global QOL > 2). The participants voided in standing on normal-to-strong desire into digital gravimetric uroflowmeter. Data of <50 ml void and intermittent flow was discarded. Reference cQ calculated using (i) Von Garrelts equations (=Q/VV(2)), (ii) cubic equations (=Q/VV(3)). Bladder volume (BV) rather than voided volume (VV) was considered for Q-V relation (BV = VV + PVR). VQI derived from present data were compared with the reference-VQI in terms of differences in area-under-curve of receiver operating characteristics. For comparing sensitivity, specificity and predictive values of study nomograms with Caucasian nomograms (Liverpool and Siroky), data of group-A and -B were plotted on each nomogram and no. of observations above and below the cutoffs (defined as equivalent to -1 SD) manually counted.

Results: Total 542 voids of group-A and 465 of group-B included for final analysis. Q-V relation was best described as [Q ∝ BV(2.4)  ≅ BV(2)]. The derived VQI (=Q/BV(2.4) ≅ Q/BV(2)) fared significantly superior to reference VQI with VV as denominator. Nomograms, constructed on Q ∝ BV(2) , were less sensitive but had higher specificity and positive predictive values compared to Caucasian nomograms.

Conclusions: Volume-normalized flow-rate index with BV as denominator (Q/BV(2)) is has highly discriminative value in screening for voiding dysfunction. Population-specific Q-BV nomograms are more specific and predictive than Caucasian Q-VV nomograms.