Why Pressure Flow Studies are preferred over Peak Flow Rate when diagnosing BOO?

Bladder outflow obstruction (BOO) is the combination of low flow rates in the presence of high voiding pressure. The symptoms of BOO can be vague and therefore, not reliable. For example, the patient may complain of poor stream, but it can due to low voiding pressure due to detrusor instability, neurogenic instability or due to poor bladder contraction. Therefore, to diagnose BOO both the flow rate and the voiding pressure should be measured at the same time.