From the Guidelines
A KUB X-ray will have limited sensitivity and specificity for detecting ureteral calculi, with a sensitivity of 53% to 62% and specificity of 67% to 69%, but may be useful in combination with US for improving stone detection rates. When interpreting the results of a KUB X-ray, it is essential to consider the patient's symptoms and medical history. The KUB X-ray will provide images of the abdominal region, focusing on the urinary tract structures, including the size, shape, and position of the kidneys, the outline of the bladder, and potentially visible portions of the ureters 1. The KUB X-ray can detect:
- Kidney stones (calcifications)
- Abnormal gas patterns
- Foreign bodies
- Gross abnormalities in organ size or position However, it has limitations, as it cannot visualize soft tissue details well 1. The KUB X-ray may also reveal:
- Calcifications in other abdominal structures like the gallbladder, pancreas, or blood vessels
- Abnormal bowel gas patterns that might indicate obstruction
- Bone abnormalities of the spine or pelvis It is crucial to note that CT is more sensitive for obstructive urolithiasis, and the combination of radiography and US may improve stone detection rates 1. In a retrospective multicenter observational cohort study, Innes et al found that adding radiography to screening for hydronephrosis increased sensitivity in all stone categories 1. Additionally, a prospective study by Faget et al found that the combination of radiograph of the abdomen and pelvis and US enabled identification of 50% of the stones that had been identified via CT, and 68% of the stones treated by urological procedures 1.
From the Research
KUB X-ray Results
The results of a Kidney, Ureter, and Bladder (KUB) X-ray can help identify various conditions, including:
- Kidney stones: A study published in 2 demonstrated that a transfer learning model with a pre-trained VGG16 empowered with explainable artificial intelligence can accurately categorize KUB X-ray images as kidney stones or normal cases with a testing accuracy of 97.41%.
- Ureteral stones: Research in 3 showed that digital post-processing of KUB images can improve the visibility of ureteral stones and stone detection, especially when stone laterality is available.
- Radiopaque and radiolucent stones: A study in 4 found that KUB can detect radiopaque stones, while CT scans are more effective in detecting radiolucent stones.
Diagnostic Performance
The diagnostic performance of KUB X-ray can be affected by various factors, including:
- Stone size and location: Studies in 4 and 3 found that stone size and location can impact the visibility of stones on KUB images.
- Imaging modality: Research in 5 suggested that different imaging modalities, such as CT scans, ultrasound, and intravenous urography, have their advantages and limitations in diagnosing and managing stone disease.
- Post-processing techniques: The use of digital post-processing techniques, such as noise estimation and reduction, can improve the visibility of ureteral stones on KUB images, as demonstrated in 3.
Clinical Applications
KUB X-ray can be used in various clinical applications, including:
- Initial diagnosis: KUB X-ray can be used as an initial imaging modality for suspected renal colic, as recommended in 5.
- Follow-up: Plain radiography, including KUB X-ray, can be used for follow-up of radiopaque stones, while ultrasound and limited IVU can be reserved for follow-up of radiolucent stones, as suggested in 5.
- Monitoring progression: KUB X-ray can be used to monitor the progression of stone burden in patients with asymptomatic calyceal stones, as recommended in 5.