The International Prostate Symptom Score (IPSS) can be utilized to measure the severity of lower urinary tract symptoms.

It is a validated, reproducible scoring system to assess disease severity and response to therapy.
The IPSS is made up of 7 questions related to voiding symptoms. A score of 0 to 7 indicates mild symptoms, 8 to 19 indicates moderate symptoms and 20 to 35 indicates severe symptoms.
It is not a reliable diagnostic tool for lower urinary tract symptoms (LUTS) suggestive of BPH, but can be used to quantitatively measure LUTS after a diagnosis is made.

The IPSS isn’t adequate for ruling in or ruling out the diagnosis of bladder outlet obstruction. In the JAMA Rational Clinical Exam paper by D’Silva et al, a cut-off of ≥20 increased the likelihood of bladder outlet obstruction (positive LR, 1.5; 95% CI, 1.1-2.0), whereas scores of less than 20 had an LR that included 1.0 in the 95% CI (negative LR, 0.82; 95% CI, 0.67-1.00).