Can a KUB (Kidney, Ureter, Bladder) X-ray be read with an NGT (Nasogastric Tube) in place?

Reading a KUB X-ray with an NGT in Place

A KUB (Kidney, Ureter, Bladder) X-ray can be accurately read with a nasogastric tube (NGT) in place, as the NGT does not significantly interfere with visualization of the urinary tract structures. The NGT appears as a radiopaque line traversing the upper abdomen but typically does not obscure critical areas needed for urinary tract evaluation.

Impact of NGT on KUB Interpretation

• The NGT is visible on KUB as a radiopaque tube extending from the nasopharynx through the esophagus and into the stomach
• The tube position is typically in the upper abdomen/stomach region, while most urinary tract structures of interest (kidneys, ureters, bladder) are in different anatomical locations
• Key urinary tract findings that remain visible despite NGT presence:
  • Urinary calculi (kidney stones)
  • Renal outlines and size
  • Bladder contour and filling
  • Most ureteral calcifications

Limitations and Considerations

• The NGT may occasionally overlap with the upper pole of the left kidney, potentially obscuring small calcifications in this specific area
• The tube may create some visual distraction but does not fundamentally impair diagnostic accuracy for most urinary tract pathologies
• KUB already has inherent limitations for urolithiasis detection regardless of NGT presence:
  • Limited sensitivity (29-72%) for stone detection compared to CT (97%) 1
  • Only 8% detection rate for stones <5mm, though 78% detection for stones >5mm 1

Clinical Context and Best Practices

• When evaluating a KUB with NGT in place:

  • Focus on the anatomical areas away from the NGT path
  • Use proper windowing/contrast settings to differentiate the NGT from calcifications
  • Consider the NGT position when evaluating the left upper quadrant

• For suspected urolithiasis requiring definitive diagnosis:

  • Non-contrast CT remains the gold standard with 97% sensitivity and 95% specificity 2
  • Ultrasound combined with KUB improves detection rates (79-90% combined sensitivity) 2, 3

Special Considerations

• For patients with indwelling NGTs requiring urinary tract imaging:
  • KUB remains a reasonable initial screening tool for large radiopaque stones
  • The presence of the NGT should be noted in the interpretation but does not invalidate the study
  • If high clinical suspicion exists for small stones or non-radiopaque stones, consider alternative imaging modalities

In summary, while an NGT creates a visible radiopaque line on a KUB X-ray, it does not prevent adequate interpretation of the study for most clinical purposes related to the urinary tract. The inherent limitations of KUB for certain diagnoses (small stones, radiolucent stones) exist regardless of NGT presence.