An Ultrasound KUB (Kidneys, Ureters, Bladder) is a safe, non-invasive imaging test that uses sound waves (not radiation) to create real-time pictures of your kidneys and bladder, and sometimes portions of the ureters (the tubes that carry urine from the kidneys to the bladder). You may also hear it called a KUB scan, kidney ultrasound, bladder ultrasound, or renal ultrasound.

This test helps your clinician assess the size, shape, and internal appearance of the kidneys and bladder, as well as how well urine is flowing through the urinary system. It can identify findings such as:

• Kidney stones (some stones are easier to see than others), bladder stones, and signs of blockage
• Hydronephrosis (swelling of the kidney due to urine backing up)
• Kidney cysts or masses (ultrasound can detect a mass, but further imaging may be needed to characterize it)
• Bladder wall thickening, bladder masses, or clots
• Post-void residual (how much urine remains in the bladder after you urinate), if your provider requests this measurement

Results are typically reported as normal (no concerning abnormalities seen) or describe specific findings. For example, a report may note “no hydronephrosis” (no urine backup), “simple renal cyst” (a common, usually benign fluid-filled cyst), “possible stone,” or “increased post-void residual” (which can suggest bladder outlet obstruction or weak bladder emptying). Your doctor interprets the ultrasound findings alongside your symptoms, urine tests, and blood work (such as kidney function tests) to decide next steps.

A KUB ultrasound is commonly ordered when symptoms or test results suggest a urinary tract or kidney problem, or when a doctor needs a radiation-free way to check for obstruction, swelling, or structural changes.

Your clinician may recommend a kidney and bladder ultrasound for:

• Flank or back pain (especially if kidney stones or blockage are suspected)
• Blood in the urine (visible blood or microscopic hematuria found on a urine test)
• Recurrent or complicated urinary tract infections (UTIs), or UTIs with fever (to look for obstruction or other contributing factors)
• Trouble urinating, weak stream, urgency/frequency, or feeling that the bladder doesn’t empty completely (often paired with a post-void residual measurement)
• Reduced kidney function on blood tests (to check for hydronephrosis or other structural causes)
• Known or suspected kidney stones—to look for stones and, importantly, for blockage caused by a stone
• Monitoring known findings such as kidney cysts, hydronephrosis, or prior stone disease
• Pregnancy or situations where radiation should be avoided (ultrasound is a preferred first-line test)

It may also be used before or after certain urology procedures, or to evaluate urinary retention (including in men with possible prostate-related obstruction). If ultrasound findings are unclear or symptoms are severe, your clinician may recommend additional imaging such as a CT scan, MRI, or specialized bladder studies.

• Kidney stones (nephrolithiasis) and ureteric stones
• Hydronephrosis and urinary tract obstruction
• Urinary tract infection (UTI) and recurrent UTIs
• Acute pyelonephritis complications (e.g., obstruction)
• Kidney cysts (simple cysts and complex cysts)
• Polycystic kidney disease (PKD)
• Bladder stones
• Urinary retention and incomplete bladder emptying (e.g., due to bladder outlet obstruction)
• Enlarged prostate (BPH) causing secondary bladder changes or hydronephrosis
• Kidney or bladder tumors/masses (screening/initial detection; may require further imaging)
• Congenital urinary tract abnormalities (e.g., duplicated collecting system, ureteropelvic junction obstruction)

• Evaluating kidney health and structure when kidney function tests are abnormal
• Checking for causes of flank pain, including suspected kidney stone episodes
• Monitoring recurrent urinary symptoms and reducing repeat infections by identifying contributing issues
• Assessing bladder emptying (post-void residual) to guide treatment for urinary retention or LUTS
• Tracking known kidney cysts or previously identified urinary tract findings over time
• Detecting urinary blockage early (hydronephrosis) to help protect long-term kidney function
• Supporting pregnancy-safe evaluation of urinary tract symptoms without radiation exposure