Nocturia is a common symptom of many conditions and is encountered in patients presenting to services across different medical specialities and health disciplines. The causal pathway of nocturia is multi-factorial and differs between patients. There is currently no symptom-specific clinical algorithm for all-cause diagnosis of nocturia. The aim of this study was to investigate the interrelationships between causes of nocturia in order to inform the development of a comprehensive multidisciplinary assessment metric.

A PubMed search that identified studies reporting relationships between nocturia and a priori aetiological factors was conducted by cross referencing the term "nocturia" with "polyuria, postural hypotension, hypertension, cardiac function, heart failure, depression, anxiety, polypharmacy, sleep disturbance, sleep disorder, apnoea, and lower urinary tract symptoms." Directed acyclic graphs (DAGS) were constructed to visually represent causal assumptions and to identify underlying relationships.

This study confirmed that causality of nocturia can be expressed in a directed acyclic graph, with the key variables being cardiovascular dysfunction, polyuria, sleep disturbance, mental health, metabolic and inflammatory changes, health status and lower urinary tract symptoms. None of the variables were independently a sufficient or necessary direct cause of nocturia and multiple backdoor pathways exist to nocturnal voiding. Polypharmacy, increasing age and BMI all have confounding effects.

There are significant interactions between voiding at night and metabolic, cardiovascular, hormonal, mental health, sleep and inflammatory changes that flag nocturia as a likely marker of co-morbid poor health. Patients should be comprehensively evaluated for all-causes of nocturia since multiple aetiologies commonly co-exist. Neurourol. Urodynam. 36:697-705, 2017. © 2016 Wiley Periodicals, Inc.