KUB for kidney stones: what to know

KUB means kidney, ureter and bladder. The test uses an X-ray image of the abdomen to look for stones that are visible on plain radiography and to assess their general position. Some stones are not visible on a KUB, and bowel gas or overlapping structures can make the image difficult to interpret.

Kidney stones can present with flank pain, abdominal pain, painful urination or difficulty passing urine. Dehydration can contribute to stone formation, but symptoms may also come from other urinary or abdominal problems. A clinician combines the examination with your history and urine or blood tests when appropriate.

Ask the imaging service whether you need any preparation and tell them if pregnancy is possible. Bring details of pain timing, urine changes, fever, vomiting and previous stones. Do not force large amounts of fluid while you are in severe pain or unable to pass urine; seek clinical guidance instead.

If a KUB does not answer the question, your clinician may suggest an abdominal ultrasound or another scan. An ultrasound can assess the kidneys and urinary tract without X-rays, although it may not identify every ureteric stone.

Get urgent medical help for severe or escalating pain with fever or chills, repeated vomiting, one functioning kidney, pregnancy, blood in the urine with worsening symptoms, or difficulty passing urine. A blocked urinary system can need prompt treatment, particularly when infection is possible.

Ask whether a KUB is suitable for the suspected stone, what the image can and cannot show, whether an abdominal ultrasound is preferable, and which symptoms mean you should return urgently. Ask how to manage pain and hydration while waiting.