Urinary retention Quiz: Ace Your Exams

A 72-year-old man presents to the emergency department for evaluation of urinary retention. The patient states he was last able to void 14 hours ago. Past medical history includes hypertension, diabetes, osteoarthritis and hyperlipidemia. Medications include amlodipine, metformin, and simvastatin. The patient occasionally takes ibuprofen for joint pain.  The patient's last A1C was 5.7. Temperature is 37°C (98.6°F), blood pressure is 167/65 mm Hg, heart rate is 99/min, respiratory rate is 18/min, and oxygen saturation is 96% on room air. On physical examination the patient appears uncomfortable, and abdominal exam is significant for  suprapubic fullness. Rectal exam is significant for an enlarged prostate and normal anal sphincter tone. Bladder scan reveals >1L. Laboratory findings and urinalysis results are detailed below. A foley catheter is placed with immediate relief of symptoms. Which of the following is the most likely underlying cause of this patient's condition?  

Laboratory value	Result	Reference
Serum chemistry
Sodium	142 mEq/L	136-145 mEq/L
Potassium	4.2 mEq/L	3.5-5.0 mEq/L
Chloride	95 mEq/L	95-105 mEq/L
Creatinine	1.7 mg/dL	0.6-1.2 mg/dL
Albumin	3.2 g/dL	3.5-5.5 g/dL
Glucose	145 mg/dL	Fasting: 70-99 mg/dL <2hr post-prandial: <120 mg/dL

Laboratory value	Result	Reference
Urinalysis
Color	Clear	Clear
Specific gravity	1.013	1.002-1.028
Glucose	negative	negative
Blood	small	negative
Leukocyte esterase	negative	negative
Nitrites	negative	negative
Leukocytes	1-2/hpf	<5/hpf
Erythrocytes	5-7/hpf	<5/hpf
Dysmorphic RBCs	Absent	Absent
Casts	none	none