CT KUB Scan Explained: Diagnosing Kidney Stones and Ureteric Colic

CT KUB is a rapid, non-contrast scan protocol used specifically for suspected renal or ureteric stones. It identifies stones as small as 1 mm, distinguishes ureteric colic from important mimics (leaking AAA, appendicitis, ovarian pathology), and gives stone location + size + Hounsfield density to guide treatment. NICE NG118 recommends CT KUB within 24 hours of adult presentation with suspected renal colic. Radiation dose has fallen dramatically with iterative reconstruction and low-dose protocols — many services now perform sub-2 mSv KUBs without loss of sensitivity. Ultrasound is preferred first-line in pregnancy (any radiation avoidance), in children (Image Gently), and in known-stone follow-up. Stone size guides management: < 5 mm most pass spontaneously (medical expulsive therapy with alpha-blocker if 5–10 mm ureteric stones); > 10 mm typically need urology intervention (ureteroscopy, shockwave lithotripsy, or PCNL); infection + obstruction is a urological emergency requiring urgent decompression (JJ stent or nephrostomy).