Urinary Tract Obstruction Workup

Updated: Jun 01, 2020
  • Author: John Samuel Fisher, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Laboratory Studies


Urinalysis can provide useful information in evaluating for infection or hematuria. White blood cells (WBCs) in the urine can indicate infection or inflammation. Nitrite- or leukocyte esterase–positive urine indicates infection.

All urine specimens that contain WBCs or are positive for nitrite or leukocyte esterase should be sent for culture and antibiotic sensitivity testing

Red blood cells can be present in patients with infection, stones, or tumor. A urologist should evaluate all patients with microscopic or gross hematuria to ensure that malignancy is not present. These patients require urine cytology and a full hematuria workup (cystoscopy, upper urinary tract imaging).

Measurement of urine pH is useful in the evaluation and workup of stones.

Basic metabolic panel

Renal insufficiency is detected on a basic metabolic panel on the basis of elevated blood urea nitrogen (BUN) and creatinine levels. This can result from bilateral renal obstructive processes or obstruction in a solitary kidney.

Other metabolic abnormalities can also be present in renal insufficiency. Hyperkalemia and acidosis may be present.

Complete blood cell count

Leukocytosis indicates infection. Anemia can be due to acute processes (eg, blood loss) or chronic processes (eg, chronic renal insufficiency, malignancy).


Imaging Studies


Ultrasonography of the kidneys and bladder is a useful imaging modality as an initial study. It is noninvasive and inexpensive and does not involve radiation exposure or depend on renal function. It is the initial study of choice in pregnant women.

In patients with allergy to intravenous pyelography (IVP) or with elevated creatinine levels, ultrasonography is a very useful source of imaging.

In children, this is often part of the initial workup for obstructive processes.

Ultrasonography is sensitive in revealing renal parenchymal masses, hydronephrosis, a distended bladder, and renal calculi. The use of color Doppler ultrasound to determine hydronephrosis grading and the absence of ureteral jets has been suggested as an accurate and noninvasive option that may limit the need for renography. [10]

The accuracy of this imaging modality depends heavily on the experience of the ultrasonographer.

In adults, if the ultrasonography findings are abnormal in any way, additional imaging is usually recommended. The combination of renal ultrasonography with flat-plate radiography of the kidneys, ureters, and bladder (KUB) is an inexpensive initial combination. See the image below.

Longitudinal image of right kidney displaying mode Longitudinal image of right kidney displaying moderate hydronephrosis.

Computed tomography

A CT scan is very useful in providing anatomic detail and is often a first-line test in the evaluation of a patient. CT provides information regarding the urinary tract, as well as any possible retroperitoneal or pelvic pathologic condition that can affect the urinary tract via direct extension or external compression.

A noncontrast CT scan should be obtained to assess for calculi. If calculi are found, a KUB film may be obtained to help determine calcium content and stone shape and to assist in monitoring the progress of the stone. Its progress can be observed with periodic simple radiography.

A contrast CT scan is needed to provide information on certain renal pathology.

If delayed contrast images are obtained, CT urography with 3-dimensional reconstruction can provide excellent visualization of the entire upper urinary tracts. A CT scan can be used to identify or rule out any other intra-abdominal processes that can cause presenting symptoms (eg, appendicitis, cholecystitis, diverticulitis, abdominal aneurysms, ovarian cysts).

See the images below.

Axial CT images with intravenous contrast, reveali Axial CT images with intravenous contrast, revealing right-sided hydronephrosis (left image) and an obstructing right ureteropelvic junction stone (right image).
Coronal CT image with intravenous contrast, displa Coronal CT image with intravenous contrast, displaying (left) delayed contrast excretion and bilateral hydronephrosis secondary to (right) bladder outlet obstruction from benign prostatic hyperplasia, and an extremely distended bladder.

Intravenous pyelography

With the advancements in CT urography, IVP is rarely performed. IVP involves the injection of contrast into the venous system and a series of KUB radiographs over time. It can be performed in patients with a normal creatinine value (< 1.5 mg/dL) for visualization of the upper urinary tract. It provides both anatomical and functional information. Patients with IVP contrast allergy cannot undergo this test.

Delayed calyceal filling, delayed contrast excretion, prolonged nephrography results, and dilatation of the urinary tract proximal to the point of obstruction characterize obstruction.

If IVP is inadequate, retrograde pyelography can be performed to completely visualize the renal pelvis or ureter.

A combination CT scan and IVP (CT/IVP) test is commonplace. CT urography, as mentioned above, is also an excellent modality.

See the images below.

Intravenous pyelogram, 1-hour delayed image showin Intravenous pyelogram, 1-hour delayed image showing left-sided hydroureteronephrosis secondary to distal ureteral obstruction.
Intravenous pyelogram displaying right-sided urete Intravenous pyelogram displaying right-sided ureteropelvic junction obstruction and normal excretory image of the left collecting system.

Radionucleotide studies

A renal scan can be performed to determine the differential function of the kidneys, as well as to demonstrate the concentrating ability, excretion, and drainage of the urinary tract. Furosemide can be administered with the renal scan to verify delayed excretion and the presence of obstruction. A technetium 99m mercaptuacetyltriglycine 3 (MAG3) renal scan is the study of choice with patients carrying a diagnosis of UPJ obstruction as the renal clearance can indicate relative renal function in these patients. A T1/2 (time to half maximum counts) of > 20 minutes indicates high-grade obstruction while a value < 10 minutes suggests no obstruction.

See the images below.

Mercaptoacetyltriglycine (MAG3) renal scan with fu Mercaptoacetyltriglycine (MAG3) renal scan with furosemide (Lasix); delayed emptying of left-sided collecting system consistent with obstructive hydronephrosis.
Mercaptoacetyltriglycine (MAG3) renal scan with fu Mercaptoacetyltriglycine (MAG3) renal scan with furosemide (Lasix); , delayed emptying of left-sided collecting system consistent with obstructive hydronephrosis.

Magnetic resonance imaging

MRI does not reveal urinary stones well and is not a first-line test used to evaluate the urinary tract. In patients who cannot tolerate a CT scan with contrast, an MRI with gadolinium can be performed to reveal any enhancing renal lesions.

MRI is useful in delineating specific tissue planes for surgical planning, as well as in evaluating the presence or extent of thrombus in a renal vein or the inferior vena cava in cases of renal tumors. While a useful tool, this imaging modality has limitations regarding the degree of obstruction in the affected kidney.

See the images below.

T2-weighted MRI, coronal image, displaying a right T2-weighted MRI, coronal image, displaying a right-sided duplicated system with obstruction of the lower pole moiety.
T2-weighted MRI, coronal image, displaying left-si T2-weighted MRI, coronal image, displaying left-sided ureteropelvic junction obstruction.

Retrograde urethrography

Radiographic dye is injected into the urethral meatus via Foley catheter at the distal urethra. Fluoroscopy is used to visualize the entire urethra for stricture or any abnormalities. This test can be particularly useful in working up lower urinary tract trauma. See the image below.

Retrograde urethrogram displaying complete obstruc Retrograde urethrogram displaying complete obstruction of prostatic urethra.

Retrograde pyelography: See Cystoscopy with retrograde pyelography.


This can be performed in patients who have a nephrostomy tube in place. Radiographic dye is injected antegrade through the nephrostomy tube. With fluoroscopy, any abnormalities or filling defects in the renal pelvis or ureter are visible. This can be safely performed even in patients with IVP contrast allergies.


Diagnostic Procedures


Cystoscopy is the placement of a small camera called a cystoscope through the urethral meatus and passing through the urethra into the bladder (see the image below). Any abnormalities in the urethra, prostatic urethra, bladder neck, and bladder can be visualized. This can be performed in the office or in the operating room.

Cystoscopy with retrograde pyelography

Retrograde pyelography is performed in the operating room with a cystoscope in the bladder. Radiographic dye is injected into each ureteral orifice. Then, with the use of fluoroscopy, any ureteral or renal pelvis filling defects or abnormalities can be visualized. The contrast load does not interfere with renal function and can be used in patients with elevated creatinine levels. It can also be used in patients with an IVP dye allergy because the contrast remains extravascular.

Flexible cystoscope; Gyrus ACMI ICN-2. Flexible cystoscope; Gyrus ACMI ICN-2.

Histologic Findings

When upper urinary tract obstruction occurs, the kidney undergoes interstitial fibrosis, with the accumulation of collagens and other extracellular matrix components.