Urinary Retention: POCUS Saves a Trip to the ED and Guides Management
This article also appears in the Southern Medical Association News at this link.
Case Presentation
A 72‑year‑old man with a known history of benign prostatic hyperplasia (BPH) and hypertension presented to his primary care clinic complaining of progressive urinary hesitancy over the previous 48 hours. He denied fever, flank pain, or gross hematuria, but reported suprapubic pressure and getting up "every hour" overnight without relief. Vitals were normal. Palpation revealed a firm, tender, midline mass above the pubic symphysis, and percussion of the lower abdomen was dull. There was no costovertebral tenderness.
Wondering whether the patient had a clinically significant post‑void residual (PVR) rather than a simple urinary tract infection, the provider reached for her ultrasound probe to answer one focused question: Is the bladder distended? The patient attempted to void, after which the clinician performed a transverse and sagittal bladder scan.
What do you see, and what’s the diagnosis?
Figure 1. Transverse bladder view with caliper measurements of width (W) and depth (D).
Figure 2. Sagittal bladder view with caliper measurement of length (L). Calculated post-void residual (PVR) volume: 513 mL.
POCUS Findings
In this case, POCUS reveals a distended bladder, the large anechoic (black) structure in the center of the image. The bladder is visualized in transverse and sagittal planes. Bladder width and depth were measured in the transverse plane. Bladder height (or length) was measured in the sagittal plane. The calculated post-void residual (PVR) is 513 mL, which is well above normal for this age group (<100-150 mL).
Bladder Volume Calculation
Many modern POCUS platforms offer one-click bladder-volume tools that use 3-D reconstruction or AI segmentation, eliminating the need to place calipers manually. With a conventional system, you measure width, depth, and height; the machine then multiplies those three values and applies a shape-correction coefficient (typically 0.52–0.75) to estimate volume.
To estimate the bladder volume manually, use the prolate ellipsoid formula:
Bladder Volume (mL) = Width (cm) x Depth (cm) x Length (cm) x 0.52
Width – transverse dimension (side-to-side)
Depth – anterior-posterior dimension
Length – cranio-caudal (sagittal) dimension
The 0.52 correction factor assumes the full bladder approximates an ellipsoid shape; multiple studies show these yields results within ± 10 % of true catheter-derived volume. [1, 2]
With AI-powered bladder-volume measurement, acquisition time drops to < 15 s, and a standardized technique flattens the learning curve for novice users.[2]
Bonus Sweep: Ruling Out Hydronephrosis
With the probe still in hand, the clinician spent an extra minute imaging both kidneys in longitudinal and transverse planes. Each kidney displayed crisp corticomedullary detail with no anechoic dilatation of the renal pelvis or calyces, signifying the absence of hydronephrosis. These normal findings reassured the provider that the bladder distention had not caused injury to the renal parenchyma. To view what a hydronephrosis looks like on ultrasound, read our article on a patient with an obstructing infected kidney stone.
Evidence
Diagnostic accuracy: Portable bladder ultrasound shows 90–95 % sensitivity with a ≤ 10 % false-positive rate versus catheterization. [3] The falls positive rate is higher when using the correction coefficient > 0.52.
Practice change: A 2010 meta-analysis found that routine ultrasound volume measurement reduced unnecessary catheterizations and catheter-associated UTI (CAUTI) risk by up to 52 %.[4]
Cost avoidance: Avoiding an emergency-department visit saves patients ≈ $650 out-of-pocket and health systems > $2 000 in charges for lower-acuity encounters.[5,6]
Workflow: AI-assisted devices provide volume estimates in < 15 s. [2] This allows for seamless integration into busy medical practices.
Case Resolution
Recognizing a post-void residual of 513 mL, the clinician inserted a Foley catheter in the clinic and drained 500 mL of clear urine, providing immediate relief. Serum creatinine was normal, and urinalysis showed no infection. The patient received tamsulosin, catheter-care instructions, and an outpatient urology referral, all without an ED transfer.
Impact of POCUS
This POCUS-guided approach delivered benefits on several levels: it provided the patient with rapid pain relief while sparing him an expensive emergency department visit; it reduced system costs by managing bladder decompression entirely in the clinic; and it improved safety, as precise bladder volume measurement justified catheter placement.
Conclusion
Acute urinary retention is common and painful, yet POCUS can diagnose it in seconds. A quick bladder scan, whether you apply the prolate ellipsoid formula or let built-in AI handle the math, immediately shows if catheterization is needed. Adding a one-minute kidney sweep rules out hydronephrosis and any upstream damage. For clinics that already use ultrasound, this two-minute bladder-plus-kidney protocol is an easy addition that enhances patient comfort, reduces costs, and keeps many cases out of the emergency department.
References
Oelke M, Hofmann R, Jonas U, Wiese B. Accuracy of a simple formula for ultrasound determination of bladder volume. J Urol. 1998;160(5):1904-1908.
Alpert EA, Gold DD, Kobliner-Friedman D, Wagner M, Dadon Z. Revolutionizing bladder health: artificial-intelligence-powered automatic measurement of bladder volume using two-dimensional ultrasound. Diagnostics (Basel). 2024;14(16):1829. doi:10.3390/diagnostics14161829
Chan DS, Young P, Kenny J, Taylor DM. Determining urinary retention in the emergency department using bedside bladder ultrasonography. Ann Emerg Med. 2003;41(6):566-571.
Palese A, Buchini S, Deroma L, Barbone F. The effectiveness of the ultrasound bladder scanner in reducing urinary tract infections: a meta-analysis. J Clin Nurs. 2010;19(21-22):2970-2979.
Rae M, Amin K, et al. Emergency department visits exceed affordability thresholds for many consumers with private insurance. KFF Health System Tracker. 2022.
Goodbill. ER Visit Cost for UTI Treatment: Most Expensive Hospitals. Goodbill Blog. Published February 17, 2022. Accessed July 10, 2025. https://www.goodbill.com/er-visit-cost-uti
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