A KUB X-ray (AP view) is a simple, quick plain X-ray of the abdomen that focuses on the Kidneys, Ureters, and Bladder (KUB). “AP view” means the X-ray beam travels from front-to-back (anterior-to-posterior) while you lie on your back. You may also hear it called a urinary plain film or a kidney stone X-ray.

This test does not measure blood or urine values. Instead, it creates a grayscale image that helps a clinician look for:

• Radiopaque stones (stones that show up on X-ray), especially some types of kidney or ureter stones
• Abdominal gas patterns and stool burden (helpful when evaluating constipation or possible bowel obstruction)
• Abnormal calcifications in the abdomen or pelvis
• Foreign bodies or the position of certain medical devices (in selected situations)

What results can mean in plain language: A “normal” KUB X-ray means no obvious abnormal calcifications, concerning bowel gas pattern, or other clear findings are seen. If a stone is visible, it may appear as a small bright/white spot along the expected path of the kidney, ureter, or bladder. However, not all stones show up on X-ray (some are radiolucent), so a normal KUB does not completely rule out a kidney stone. If the image shows too much stool or a concerning gas pattern, it may suggest constipation or, less commonly, bowel blockage—your clinician will interpret this along with your symptoms and other tests.

A provider may order a kub x-ray for fast, first-look information when symptoms suggest a urinary or abdominal problem. It’s commonly used because it’s widely available, quick, and involves less radiation than a CT scan (though it still uses a small amount of radiation).

Common reasons to order a KUB X-ray AP view include:

• Suspected kidney stones or ureteral stones, especially to look for radiopaque stones or to track a known stone over time (e.g., before/after treatment)
• Flank or lower abdominal pain, sometimes with nausea or pain that comes in waves (renal colic)
• Blood in the urine (hematuria), when a stone is part of the differential diagnosis
• Urinary symptoms such as urgency, burning, or difficulty urinating—when combined with other findings, to evaluate for complications
• Constipation, bloating, abdominal distension, or suspected stool buildup
• Possible bowel obstruction or abnormal bowel gas pattern (often alongside other imaging, depending on severity)
• Follow-up after procedures in some settings (for example, checking the location of certain stents or devices when clinically appropriate)

Your clinician may choose other imaging depending on the question being asked. For example, a CT scan is often the most sensitive test for kidney stones, while ultrasound is commonly used in pregnancy or when minimizing radiation is important.

• Kidney stones (nephrolithiasis)
• Ureteral stones (ureterolithiasis)
• Bladder stones (vesical calculi)
• Constipation / fecal impaction
• Bowel obstruction (suspected)
• Urinary tract obstruction or hydronephrosis (indirect signs; may require ultrasound/CT for confirmation)
• Abdominal or pelvic calcifications (e.g., phleboliths; may mimic stones)

• Identifying and monitoring kidney stone burden to guide treatment and help prevent recurrence
• Checking for visible urinary stones as part of evaluating flank pain or suspected renal colic
• Assessing constipation severity (stool burden) to support symptom relief plans
• Evaluating abdominal symptoms by reviewing bowel gas patterns when obstruction is a concern
• Supporting follow-up care after stone treatment (e.g., confirming whether a radiopaque stone has moved or passed)