What is the appropriate workup for an adult patient presenting with nocturnal urination?

Workup of Nocturnal Urination

Begin with a 72-hour bladder diary to quantify nocturia severity and distinguish between nocturnal polyuria, reduced bladder capacity, and global polyuria—this is the single most important diagnostic tool that will guide all subsequent management decisions. 1

Initial Assessment

Establish Impact and Severity

• Document the number of nocturnal voids and overnight urine volume to determine if this meets diagnostic criteria for nocturia (≥1 void per night) and assess functional impairment the following day 1
• Assess quality of life impact using validated questionnaires to determine treatment thresholds 1, 2

Medical History Review: The "SCREeN" Framework

Systematically evaluate for five categories of conditions that commonly cause nocturia 1:

• Sleep disorders: Obstructive sleep apnea (ask about gasping/choking at night, morning headaches, daytime sleepiness), insomnia, restless legs syndrome, parasomnias 1
• Cardiovascular: Hypertension, congestive heart failure (ask about ankle swelling, dyspnea on exertion) 1
• Renal: Chronic kidney disease 1
• Endocrine: Diabetes mellitus, thyroid disorders (hyper or profound hypothyroidism), diabetes insipidus, pregnancy/menopause, testosterone deficiency (ask about excessive thirst) 1
• Neurological: Most neurological diseases are potentially relevant (ask about leg control problems, tremor, gait abnormalities, orthostatic lightheadedness) 1

Medication Review

Identify drugs that may cause or worsen nocturia 1:

• Diuretics (note timing relative to bedtime)
• Calcium channel blockers
• Lithium
• NSAIDs
• Medications causing xerostomia (dry mouth leading to increased fluid intake): anxiolytics, antidepressants (especially tricyclics), antimuscarinics, antihistamines, decongestants, antiparkinsonians, pain medications, antipsychotics 1
• Alcohol and caffeine (diuretic effects) 1

Physical Examination

Perform a focused examination looking for 1:

• Abdominal examination
• Rectal/genitourinary examination (prostate in men, pelvic organ prolapse in women)
• Peripheral edema (suggests cardiac or renal disease)
• Signs of reduced salivation or scleroderma (xerostomia)
• Lower limb weakness, gait abnormalities, speech disturbance, tremor (neurological disease)
• Assessment of cognitive function and ability to dress independently (impacts treatment goals) 1

Baseline Laboratory Investigations

Obtain the following tests for all patients 1:

• Urinalysis to rule out UTI and hematuria 1
• Blood tests: Electrolytes/renal function, thyroid function, calcium, HbA1c 1
• Urine albumin:creatinine ratio 1
• Blood pressure assessment 1
• Pregnancy test where applicable 1

Critical Diagnostic Tool: 72-Hour Bladder Diary

This frequency-volume chart is essential to differentiate 1, 3:

• Nocturnal polyuria: >33% of 24-hour urine output occurs at night (normal or large volume voids) 1, 4, 5
• Global polyuria: Total 24-hour output >3 liters 1, 5
• Reduced bladder capacity: Small volume voids throughout day and night 1

Optional Additional Testing (At Clinician Discretion)

Post-Void Residual

Measure PVR in patients with 1:

• Obstructive symptoms
• History of incontinence or prostatic surgery
• Neurologic diagnoses
• Not necessary for uncomplicated patients receiving first-line behavioral interventions 1

Urine Culture

Consider when urinalysis may be unreliable 1

Advanced Investigations (When Initial Workup Suggests Specific Conditions)

For Suspected Sleep Disorders

• In-depth questionnaires (e.g., STOP-BANG for OSA) 1
• Overnight oximetry (referral to respiratory or ENT sleep clinic) 1
• Ferritin level for restless legs syndrome (supplementation if <75 ng/ml) 1

For Suspected Cardiovascular Disease

• Electrocardiogram 1
• Brain natriuretic peptide; echocardiogram if positive 1

For Renal Disease

• Renal ultrasound (per local CKD guidelines) 1

For Suspected Endocrine Disorders

• Morning urine osmolarity after overnight fluid avoidance (>600 mosm/L rules out diabetes insipidus; indicated for patients urinating >2.5 L per 24 hours despite fluid restriction attempts) 1
• Parathyroid hormone if hypercalcemia detected 1

For Neurological Disease

• Lying/standing blood pressure (within 1st minute and at 3 minutes; fall of 20 mmHg systolic or 10 mmHg diastolic indicates orthostatic hypotension suggesting autonomic failure) 1

Common Pitfalls to Avoid

• Do not assume a medical condition causes nocturia without establishing a clinical link (e.g., successful treatment of the condition leading to simultaneous reduction in nocturia) 1
• Do not proceed with urodynamics or cystoscopy in initial evaluation unless specific indications exist (hematuria not from infection, neurological disease, treatment failure) 1
• Distinguish nocturia from enuresis (bedwetting without waking) which requires different evaluation 1
• In patients with predominant nocturia (≥2 voids per night), complete the bladder diary BEFORE initiating empiric treatment to avoid treating the wrong underlying mechanism 1, 3

Red Flags Requiring Specialist Referral

Refer to urology before treatment if 1:

• DRE suspicious for prostate cancer
• Hematuria (after ruling out infection)
• Abnormal PSA
• Pain
• Recurrent infections
• Palpable bladder
• Neurological disease
• New-onset severe LUTS with unusual features (e.g., enuresis without chronic retention) 1