Diagnostic Approach to Suspected Renal Colic
Case: You’re seeing a 43-year-old female who reports three-months of pain in her left groin radiating to her left flank area. The pain comes in waves, lasts minutes, and is severe. She says she has a hard time getting comfortable. She does not have dysuria, urgency, frequency, unusual vaginal discharge, or abdominal pain. She is not having pain on exam in your outpatient office today. You suspect renal colic.
What is renal colic? Simply put, it is sudden, intermittent, acute pain from a kidney stone blocking the urinary tract (urolithiasis). Pain occurs due to ureteral peristalsis (rhythmic contraction) and the stone moving through the urinary tract (1). Typical symptoms include pain that originates in the flank then radiates to the groin; in men this can radiate to the testicles and in women can radiate to the labia. The pain is unilateral. Other signs and symptoms may include nausea, vomiting, and hematuria (1).
Diagnostic Approach: for your 43-year-old female in an outpatient setting, you first rule out importance differential diagnoses.
The RED FLAGS of renal colic
Back to the case: You rule out red flags, her vitals are stable, she is afebrile, and she does not have CVA tenderness. Next, you determine it is reasonable to check a urine dip which is positive for red blood cells, negative for leukocytes and nitrites. Hematuria is common in urolithiasis, and you have ruled out infection based on history, physical exam, and urine dip. You are confident in your diagnosis of urolithiasis, but you ask yourself if diagnostic imaging is warranted.
Role for Imaging in Renal Colic
Ultrasound (KUB): is not as sensitive as a CT scan for detecting kidney stones but is a good screening test as it will detect hydronephrosis and is unlikely to miss stones requiring intervention (2). It can be done in the emergency department, is often more accessible as an outpatient and does not expose the patient to radiation. Also ideal for pregnancy or pediatric populations to reduce radiation exposure (2).
Abdominal x-ray: this modality can be used in combination with ultrasound but is less sensitive than CT (consider under special circumstances e.g. pregnancy to reduce radiation exposure) (3). Also, some types of stones are not visualized on x-ray.
CT KUB: the most sensitive and specific test for kidney stones but is not always required. Consider a CT scan for atypical symptoms of renal colic, in older patients, if initial ultrasound did not reveal kidney stone(s) or hydronephrosis (rule out other etiologies of pain), or if pain is not relieved by adequate analgesia (2). Order a low-energy unenhanced CT (3). Standard-dose CT is recommended for BMI >30 (or males >130kg, females >115kg). Stone size and location are used to predict the likelihood of spontaneous passage and can help guide management.
Back to the case: You decide to order a KUB ultrasound and recommend analgesia to manage the pain, discuss adequate fluid intake, and review emergency department precautions.
What about stone size? Most stones <5mm will pass spontaneously. For stones >5mm in diameter, there is a progressive decrease in the spontaneous passage rate, but if they are <10mm outpatient management might be appropriate. Stones >10mm or located in the proximal ureter/ureteropelvic junction are less likely to pass spontaneously.
When should I think of referring to urology for urolithiasis? If imaging detects a stone of >10mm, if conservative management was tried for 4 weeks (e.g. alpha blocker, fluids), or if persistent/worsening pain. Also, if a patient has a stone and signs or symptoms of a urinary tract infection or pyelonephritis these patients need to be seen in the ED!
Key Take Home Points:
Ultrasound is a reasonable screening test in the emergency department or in the outpatient setting for your patient presenting with typical signs and symptoms of renal colic.
If there is diagnostic uncertainty or you are trying to rule out other etiologies of pain, low-dose unenhanced CT is preferred.
References/readings:
Golzari SE, Soleimanpour H, Rahmani F, Zamani Mehr N, Safari S, Heshmat Y, et al. Therapeutic approaches for renal colic in the emergency department: a review article. Anesthesiology and pain medicine. 2014;4(1):e16222-e. (VIEW HERE)
Moore CLMD, Carpenter CRMDM, Heilbrun MEMD, Klauer KDOEJD, Krambeck AMD, Moreno CMD, et al. Imaging in Suspected Renal Colic: Systematic Review of the Literature and Multispecialty Consensus. Annals of emergency medicine. 2019;74(3):391-9.
Canadian Association of Radiologists. Canada. 2021-2022 [2022; June 25, 2023]. Available from: https://car.ca/patient-care/referral-guidelines/