The Interpretability of the Neurogenic Bladder Symptom Score

OBJECTIVE: To define mild, moderate and severe symptom categories of the neurogenic bladder symptom score (NBSS) and NBSS-short form (SF), and to calculate the minimal clinically important difference (MCID) of the NBSS-SF. METHODS: We used existing datasets from the original NBSS validation study (n = 230 patients with spinal cord injury (SCI), multiple sclerosis, and spina bifida), and a large cross-sectional study of people with SCI (n = 1479) who completed the NBSS. We used the previously validated mild-moderate-severe categories of the ICIQ-UI, IPSS, and the SCI-QOL Bladder complications scale to define patients with mild, moderate or severe symptoms, and mapped these to the NBSS scores for the related NBSS domains of incontinence, storage/voiding, and consequences, respectively. We validated these NBSS score categories using four data sets, and by examining the global bladder problem rating. An anchor-based MCID of the NBSS-SF was determined. RESULTS: Using the median/interquartile range of the associated NBSS domain score of people who were in the moderate category of the ICIQ-UI, IPSS, and the SCI-QOL Bladder complications, we calculated the severity categories for the NBSS total score: 0-32 (mild), 33-48 (moderate), and 49-74 (severe). These score categories produced significantly different NBSS scores in 29/32 comparisons in four different study populations. The global bladder problem had good agreement with each domain's categorical scale. Finally, the group-level MCID of the NBSS-SF total score was calculated as an improvement of 1.8. CONCLUSIONS: We have determined interpretability ranges for the NBSS and NBSS-SF. This can help interpret patient and clinical study results.