KUB X-Ray
The KUB film (kidneys, ureters and bladder) is a supine anteroposterior abdominal radiograph centred on the lower abdomen, covering from the upper poles of the kidneys to the pubic symphysis. It shows the renal outlines, the course of the ureters and bladder region, and radio opaque stones.
The ureters run along the tips of the lumbar transverse processes, cross the sacroiliac joints and pass the ischial spines to reach the bladder, with three physiological narrowings (pelviureteric junction, pelvic brim and vesicoureteric junction) where stones lodge.
Radio opacity depends on composition: calcium oxalate and calcium phosphate stones (about 80 to 85% of stones) are opaque, struvite and cystine are less dense (cystine is faintly opaque), and uric acid, xanthine and indinavir stones are radiolucent.
Overall, 80 to 90% of stones are visible on a KUB, but sensitivity for ureteric stones is lower (about 45 to 60%) because of bowel gas, faeces, bones and phleboliths, and stones under 4 mm are often missed. The dose is about 0.7 mSv.
KUB is no longer the first test for renal colic. Non-contrast low dose CT (sensitivity 95 to 98% and specificity about 97%) and ultrasound (hydronephrosis, renal stones, and no radiation) have replaced it for diagnosis.
KUB is useful for follow up of known opaque stones during conservative treatment, stone size and position before shockwave lithotripsy or ureteroscopy, post-treatment clearance, and the position of ureteric stents and urinary catheters. Combined with ultrasound it gives acceptable accuracy for diagnosis in low resource settings.
Indications. Follow up of a known radio opaque renal or ureteric stone during medical expulsive therapy. Planning for shockwave lithotripsy (stone location and density). Assessment after lithotripsy or ureteroscopy. Position of ureteric stent, nephrostomy tube, urinary catheter or retained device. Suspected nephrocalcinosis or calcified masses.
Scout film before intravenous urography. Renal colic where CT is not available (together with ultrasound). Not for the initial diagnosis of acute loin pain, haematuria without stone history, or renal masses.
Contraindications and precautions. Pregnancy: avoid; ultrasound is first line and MRI is used when needed. Previous barium studies, gas, faeces and constipation reduce image quality, so patients may be given a laxative the day before for planned studies. Remove clothing with metal and external devices.
Preparation and technique. Supine film at end expiration, with the lower border of the film at the pubic symphysis and the upper border covering the renal outlines. Additional views include oblique films for stones overlying bone and a coned bladder view. A tomogram or low dose CT scout can help.
