Are follow-up scans necessary after an episode of renal colic?

Follow-Up Imaging After Renal Colic

All patients with renal colic, whether managed at home or in hospital, should be offered fast-track urological investigation with follow-up imaging to confirm stone passage, assess for complications, and guide further management. 1

Risk-Stratified Approach to Follow-Up Imaging

Low-Grade Stones (Small, Uncomplicated)

• Routine follow-up imaging is NOT required for minor renal injuries or small stones without complications 1
• If the patient had a clear diagnosis, responded well to analgesia, and passed the stone (confirmed by straining urine), extensive imaging may not be necessary 1
• However, all patients still need urological follow-up within 7 days to determine: 1
  • Was a calculus identified and what was its size/location?
  • If a calculus is still present, is intervention needed?
  • Should alternative diagnoses be considered?
  • Is the patient at risk for recurrent episodes?

Moderate to Severe Cases (Stones with Hydronephrosis or Complications)

• Follow-up imaging is clinically driven and necessary when symptoms change or stone passage needs confirmation 2, 3
• For stones causing hydronephrosis, periodic imaging to monitor stone position and assess obstruction is recommended 3
• If medical expulsive therapy fails after 4-6 weeks, imaging must be performed before offering definitive treatment 2

Timing and Modality of Follow-Up Imaging

Initial Follow-Up (Within 7 Days)

• The American College of Radiology recommends that the majority of patients receive a radiology appointment within 7 days of symptom onset 1
• Non-contrast CT of the abdomen and pelvis is the most accurate modality (sensitivity 97%, specificity 95%) for detecting stones and assessing complications 2
• Low-dose CT protocols should be used to minimize radiation exposure while maintaining diagnostic accuracy 2

Alternative Imaging Options to Reduce Radiation

• Ultrasound of the kidneys and bladder is an acceptable alternative (appropriateness rating 7), particularly for evaluating hydronephrosis 2
• Combined ultrasound and KUB radiography can improve sensitivity while reducing radiation exposure 1
• For patients requiring multiple imaging studies due to recurrent stones, ultrasound should be considered for follow-up when appropriate 2

Red Flags Requiring Urgent Imaging

Perform immediate follow-up imaging if any of the following develop: 3

• Evidence of urinary tract infection (fever, shivering, leukocytosis have 95-98% specificity for need for intervention) 4
• Intractable pain despite adequate analgesia
• Worsening obstruction or hydronephrosis
• Abrupt recurrence of severe pain 1

Common Pitfalls to Avoid

• Do not assume all small stones will pass spontaneously—the presence of hydronephrosis indicates higher risk of passage failure 3
• The absence of hydronephrosis on ultrasound does not rule out kidney stones (negative predictive value only 65%) 2
• Ultrasound alone has limited sensitivity for detecting kidney stones, particularly smaller stones (<3mm) or those in non-dilated systems 2
• Do not delay urological referral if infection is suspected—untreated bacteriuria with obstruction can lead to urosepsis 3
• Stones larger than 6.5mm with attenuation >1100 HU and proximal location are more likely to require intervention 4

Special Populations

Pregnant Patients

• Ultrasound is the first-line imaging modality (appropriateness rating 8) 2
• MRI without contrast can be considered as second-line if ultrasound is inconclusive 2
• Low-dose non-contrast CT should only be used as a last resort in pregnancy 2

Recurrent Stone Formers

• For patients with recurrent stones requiring multiple imaging studies, review previous images to understand stone history and limit the CT scan field to the area of interest 2
• Use the lowest possible radiation dose for CT scans and consider ultrasound for follow-up 2