What could be causing my frequent urination with small voids of 150ml, given that I don't have diabetes or a urinary tract infection (UTI) and I'm currently taking escitalopram (Lexapro)?

Frequent Urination with Small Voids: Likely Causes and Evaluation

Your frequent urination with small 150ml voids most likely represents reduced functional bladder capacity from either medication effect (escitalopram can rarely cause urinary retention leading to overflow frequency), overactive bladder syndrome, or an anatomical problem reducing bladder storage—and you need post-void residual measurement immediately to distinguish between these mechanisms. 1, 2

Immediate Diagnostic Priority: Rule Out Urinary Retention

Your 150ml voided volumes are concerning for incomplete bladder emptying with overflow frequency rather than true frequent urination. 1

• Measure post-void residual (PVR) volume urgently using bladder ultrasound—this single test distinguishes between reduced bladder capacity versus urinary retention with overflow. 1
• PVR >150ml indicates significant retention and contraindicates certain medications while requiring different management. 1
• If PVR is elevated, escitalopram is the prime suspect—SSRIs rarely cause acute urinary retention through serotonergic effects on bladder sphincter control, and case reports document escitalopram specifically causing this problem. 3, 4

Escitalopram as a Causative Factor

Escitalopram can cause urinary retention, though this adverse effect is not prominently listed in standard prescribing information and is easily overlooked. 5, 3

• The FDA label for escitalopram lists "difficult urination" as a side effect in pediatric/adolescent populations but does not emphasize retention risk in adults. 5
• Published case reports document escitalopram-associated acute urinary retention that resolved completely after drug discontinuation without need for continued catheterization. 3
• SSRIs including sertraline cause urinary hesitancy and retention through serotonergic modulation of bladder sphincter tone—escitalopram likely acts through the same mechanism. 4
• If your PVR is elevated, discontinuing escitalopram should be strongly considered after psychiatric consultation, as normal micturition typically resumes after stopping the medication. 3

Alternative Diagnosis: Overactive Bladder with Reduced Functional Capacity

If your PVR is normal (<150ml), you likely have overactive bladder (OAB) with reduced functional bladder capacity rather than retention. 1

Anatomical Causes to Evaluate

• Bladder wall abnormalities including cystoceles, bladder diverticula, or prior pelvic surgery can reduce functional capacity and cause frequent small voids. 1, 2
• Chronic bladder wall inflammation or fibrosis causes progressive smooth muscle dysfunction, reducing bladder compliance so the bladder cannot stretch adequately during filling. 2
• Post-void residual measurement combined with bladder ultrasound reveals structural abnormalities including wall thickening and anatomical defects. 2

Functional Overactive Bladder

• Detrusor overactivity causes urgency-driven frequent small voids without anatomical pathology—this is a diagnosis of exclusion after ruling out retention and structural problems. 1
• Frequency-volume charts documenting each void help distinguish true reduced capacity (consistently small voids) from polyuria (normal/large volume voids). 2

Critical Diagnostic Algorithm

Follow this sequence to identify the cause:

1. Measure post-void residual immediately 1

   • PVR >150ml = urinary retention → suspect escitalopram, consider discontinuation 1, 3
   • PVR <150ml = proceed to step 2

2. Obtain bladder ultrasound to assess for structural abnormalities including wall thickening, diverticula, or masses 2

   • Abnormal anatomy → refer to urology for further evaluation
   • Normal anatomy → proceed to step 3

3. Complete 3-day frequency-volume chart documenting time and volume of each void 2

   • Consistently small voids (<200ml) = reduced functional capacity
   • Variable or normal volumes = consider polyuria from other causes

4. If all above normal, diagnose overactive bladder and consider antimuscarinic or beta-3 agonist therapy 1

Common Pitfalls to Avoid

• Never assume normal voiding without measuring PVR—subjective urinary retention can exist without patient awareness, and escitalopram-induced retention is easily missed because it's rarely reported. 3
• Don't start antimuscarinic medications if PVR >150ml—this will worsen retention and potentially precipitate acute urinary retention requiring catheterization. 1
• Bladder wall thickening on imaging may represent detrusor overactivity rather than reduced capacity—urodynamic studies may be needed for definitive diagnosis if imaging is equivocal. 2