Do you need to be Nil Per Os (NPO) for a renal ultrasound (US)?

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Last updated: April 19, 2025View editorial policy

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From the Guidelines

No, you do not need to be NPO for a renal ultrasound. You can eat and drink normally before this procedure. A renal ultrasound is a non-invasive imaging test that uses sound waves to create pictures of your kidneys and surrounding structures. Unlike some other imaging studies, renal ultrasounds don't require fasting. The kidneys can be adequately visualized regardless of your food or fluid intake. In fact, having some fluid in your system may actually be beneficial as a full bladder can sometimes provide a better acoustic window for imaging the kidneys, especially the lower portions. According to the American College of Emergency Physicians 1, emergency ultrasound imaging, including renal ultrasound, should occur as soon as the clinical decision is made that the patient needs a sonographic exam, without any specific requirements for fasting or NPO status. Some key points to consider include:

  • Renal ultrasounds are non-invasive and do not require any special preparation, such as fasting or NPO status.
  • Having some fluid in your system may be beneficial for imaging the kidneys.
  • Specific instructions may vary by facility, so it's always best to follow any pre-procedure guidelines provided by your healthcare provider or the imaging center where your ultrasound is scheduled.
  • The primary goal of a renal ultrasound is to provide immediate information for further evaluation, management, and interventions, and it is the responsibility of the supervising physician to perform and interpret the exam 1.

From the Research

NPO Status for Renal Ultrasound

  • There is no direct evidence in the provided studies that suggests the need for NPO (nil per os) status for renal ultrasound examinations.
  • The studies focus on the use of ultrasound in nephrology for diagnostic and procedural purposes, highlighting its importance and applications in the field 2, 3, 4, 5.
  • Ultrasound imaging is described as a non-invasive and nonionizing radiation technique, making it a suitable initial radiographic test for patients with abnormal kidney function 5.
  • The use of ultrasound in emergency settings, such as in the case of multiple renal infarctions, is also demonstrated, where it played a crucial role in diagnosis 6.
  • However, none of the studies mention the requirement for NPO status prior to undergoing a renal ultrasound, suggesting that it may not be a necessary precaution for this type of examination 2, 3, 4, 5, 6.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Renal relevant radiology: use of ultrasound in kidney disease and nephrology procedures.

Clinical journal of the American Society of Nephrology : CJASN, 2014

Research

The Nephrologist as an Ultrasonographer.

Advances in chronic kidney disease, 2020

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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