EM@3AM: Urolithiasis

Author: Daniel Tauber, MD (EM Resident Physician, UTSW / Parkland Memorial Hospital) // Reviewed by: Alex Koyfman, MD (@EMHighAK) and Brit Long, MD (@long_brit)

Welcome to EM@3AM, an emDOCs series designed to foster your working knowledge by providing an expedited review of clinical basics. We’ll keep it short, while you keep that EM brain sharp.

A 34-year-old male with no significant PMH presents to the ED for 12 hours of intermittent, sharp, left-sided flank pain with radiation to his groin. He took ibuprofen with minimal relief, but came to the ED when he noticed blood-tinged urine. He has also experienced severe nausea without emesis and is afebrile. He denies chest pain, abdominal pain, or dysuria.

On exam, his vital signs include BP 145/87, HR 94, T 98.6 Oral, RR 16, SpO2 100% on RA. He appears uncomfortable, writhing in bed. His cardiopulmonary and abdominal exams are normal. He has CVA tenderness on the left, but no signs of external trauma. His GU, including the testicles is normal.

What is the patient’s diagnosis? What’s the next step in your evaluation and treatment?

Answer: Urolithiasis (Kidney Stone)



  • Lifetime prevalence is 5-12%, with a greater predominance in adult men than women (2-3x more likely in men).1
  • Higher prevalence in hot, dry, arid climates such as mountain, desert, or tropical regions.
  • More recently, an increase in kidney stone prevalence in individuals younger than 20 years old has been found.2
  • Diabetes and obesity are strongly associated with the formation of kidney stones.3
  • Recurrence rates: 37% within the first year, 50% within 10 years, and 75% within 20 years.3


Risk Factors:

  • Obesity, dehydration, excess meat intake, excess sodium intake, metabolic syndrome.3
  • Family history or personal history of urolithiasis, gout, bowel surgery/IBD.
  • Primary hyperparathyroidism and prolonged immobilization (increased bone turnover).


Pathophysiology: When dissolved salts become supersaturated in the urine, they condense and form a stone. Most common stones (80%) are calcium oxalate or calcium phosphate.3  Increased solvent (hydration), as well as citrate and magnesium, are inhibitory substances for crystal precipitation.

  • Randall’s plaque is a collection of interstitial suburothelial that acts as a nidus for calcium phosphate particles to condense.3
  • Increased calcium excretion: hyperparathyroidism, absorptive and renal hypercalciuria, sarcoidosis, loop diuretics, IBD.4
  • Restrictive calcium diets paradoxically increase risk of stone formation due to the lack of calcium to bind with oxalate in the gut.3
  • Struvite stones (magnesium-ammonium-phosphate) account for 10% of stones and are caused by urea-splitting bacteria – Proteus, Klebsiella, Staphylococcus species. 3
  • Uric acid stones account for 10% of cases, and 25% of patients with gout develop a uric acid stone.4


Anatomy: Ureters are hollow viscus organs that came become completely or partially obstructed from a kidney stone. Obstruction of a ureter can cause hydronephrosis, and the increased pressure against Gerota’s fascia results in flank pain.3

  • Migrating nonobstructing stones cause intermittent, colicky pain due to ureteral irritation.
  • During acute obstruction, most post patients do nothave a rise in Cr because the opposite kidney can compensate up to 185% of baseline function.3
  • Common stone locations: Ureteropelvic junction (UPJ), pelvic brim, and ureterovesicular junction (UVJ).
  • Passage rate within 4 weeks: <5mm – 98%; 5-7mm – 60%; >7mm – 39%.3


Clinical presentation:

  • Classic symptoms: acute, crampy, intermittent flank pain with radiation to groin.
  • Patients typically appear uncomfortable due to severe pain.
  • Additional symptoms: rebound tenderness (29%), guarding (61%), rigidity (8%), N/V (50%).3
  • Hematuria present 85%, with only 30% of patients demonstrating gross hematuria.3


Differential diagnosis:3,5

  • Vascular: Aortic dissection, AAA, renal artery embolism, renal vein thrombosis, mesenteric ischemia.
  • Renal: Pyelonephritis, papillary necrosis, RCC, Renal infarct, Renal hemorrhage
  • Ureter: Stricture, blood clot, tumor
  • Bladder: Tumor, cystitis, UTI
  • GI: Biliary colic, pancreatitis, PUD, appendicitis, inguinal hernia, diverticulitis, cancer, bowel obstruction
  • Gyn: Ectopic, PID/TOA, ovarian cyst, ovarian torsion, endometriosis
  • GU: Testicular torsion, epididymitis
  • Other: Shingles, drug-seeking, Retroperitoneal hemorrhage

*Note: If the patient is >60 years old with first time flank pain, think AAA first, not kidney stone.


Physical Exam:

  • Intermittent flank pain is common in patients with acute urolithiasis.
  • Patients will appear uncomfortable, often moving around in bed rather than lying still.
  • CVA tenderness may or may not be present. If it is present, should be located on the same side as stone.
  • Genitalia should be nontender and have no evidence of external trauma.



  • All women of childbearing age should be tested for pregnancy.
  • Urinalysis with hematuria (>3 RBC/hpf) will be present 85% of time.3
  • 24% of patients with flank pain + hematuria will have no radiological evidence of a kidney stone.6
  • If UA is suggestive of infection, obtain a urine culture and empirically treat prior to sensitivity results.7
  • CBC has limited utility if patient is afebrile and otherwise well appearing.
  • Evaluation of renal function and electrolytes is useful for assessing renal function, especially when prior Cr available.

Note: +/- hematuria does not rule in/out kidney stone, only aids in overall likelihood.


Imaging: Useful to confirm diagnosis of kidney stone, as well as evaluate for other diagnoses.

  • The AUA recommends a CT noncontrast for first time renal colic patients who are not pregnant and >14 years old.8
  • Imaging can be deferred until patient has follow-up appointment if they have a history of kidney stones and similar prior presentations.3
  • CT noncontrast hassensitivity 94-97% and specificity 96-99%.9
  • Low dose CT is as sensitive as standard CT for stones >3 mm and BMI <30; the AUA recommends low dose as first line in patients with BMI <30.8,10
  • X-rays (KUB film) have poor sensitivity (29-58%) and poor specificity (69-74%) and are not recommended as a first line diagnostic test.11
  • For young patients and pregnant woman, bedside US can be a first line option.
  • US is better at identifying proximal and distal ureteral stones, but has poor sensitivity of detecting mid-ureteral stones and is heavily operator-dependent.3
  • Overall US has a sensitivity of 80% [95% CI 63-85%]; specificity of 83% [95% CI 61-94%], and accuracy of 81% [95% CI 69-89%]3,12



  • IV hydration has no impact on stone passage; provide IVF if dehydration present on exam.13
  • NSAIDs are preferred because they inhibit of prostaglandin synthesis and cause ureteral relaxation.3
  • Ketorolac 15 mg IV, 30 mg IM, or ibuprofen 400 mg PO Q6H PRN14
  • Metoclopramide is the only antiemetic to be studied in renal colic and alone provides equivalent pain relief to opioids in addition to treating nausea.3
    • Administer metoclopramide 10 mg IV.
  • Patients with fever, renal insufficiency, or systemic signs of infection require antibiotics.
    • IV gentamicin 3.0 mg/kg/d divided Q8H plus ampicillin 1-2 g IV Q4H3
    • IV Zosyn 3.375 g Q6H3
    • IV Cefepime 2 g Q8H3
    • IV Ticarcillin-clavulanic acid 3.1 g Q6H3
    • IV Ciprofloxacin 400 mg Q12H3
    • IV Ceftriaxone 1 g IV



  • Patients with stones should have primary care or urology follow-up within 7 days.3
  • If stone passes in ED, elective urology follow-up is recommended.3
  • For those with >5 mm stones, irregular shaped, or proximal stones lower passage rates, discuss pros/cons with patient regarding intervention versus watch and wait.
  • Discuss with urology when renal insufficiency, intractable pain/vomiting, severe comorbidities, associated infection, multiple ED visits, or single kidney/transplant kidney is present, and plan for admission.3
  • Average passage for 5-6 mm stone is 7-30 days.3
  • Oral Opiate and NSAIDs should be provided for pain control.
  • Discharge instructions: Return to ED for fever, vomiting, PO intolerance, inability to urinate, uncontrolled pain.3

A 33-year-old woman with a history of frequent urinary tract infections presents to the Emergency Department with right flank pain and dysuria that started acutely today. The pain is associated with a low grade fever, nausea, and vomiting. Urinalysis is positive for leukocyte esterase and nitrites. Microscopic examination reveals 26 WBC/hpf and 2+ bacteria. A noncontrast abdominal computed tomography scan shows a staghorn calculus in the right kidney. Which of the following is the likely composition of the staghorn calculus?

A) Calcium oxalate

B) Cystine

C) Magnesium, ammonium, and phosphate

D) Uric acid



Answer: C

Urologic stone formation is the result of supersaturation of dissolved salts in the urine which then condense into a solid. Struvite (magnesium-ammonium-phosphate) stones account for about 10-15% of all stones. They occur almost exclusively in patients with urinary tract infections caused by urea-splitting bacteria such as Proteus, Klebsiella, Providencia, Pseudomonas, and Staphylococcus species. They are also the most common cause of staghorn calculi (large stones that cause a cast of the renal pelvis). Treatment of staghorn calculi is difficult as antibiotic penetration of the stone is poor and the risk for urosepsis exists as long as the stone remains.

Most stones are comprised of calcium oxalate (A), either alone or in combination with calcium phosphate. Cystine (B) stones are rare and occur in patients with cystinuria, an autosomal recessive genetic disorder affecting amino acid transport. Uric acid (D) stones account for about 10% of cases of urolithiasis. These stones are radiolucent on abdominal radiograph.

Rosh Review Free Qbank Access

Further Reading: 



Core EM

emDocs – Renal Colic Mimics

emDocs – The Sick Kidney Stone Patient

Rebel EM – Tamsulosin 



  1. Norlin A, Lindell B, Granberg PO, et al. Urolithiasis. A study of its frequency. Scand J Urol Nephrol. 1976;10(2):150-3.
  2. Tasian GE, Ross ME, Song L, et al. Annual incidence of nephrolithiasis among children and adults in South Carolina from 1997 to 2012. Clin J Am Soc Nephrol. 2016 Mar 7;11(3):488-96.
  3. Manthey DE, Nicks BA. Urologic Stone Disease. In: Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e New York, NY: McGraw-Hill; 2016.
  4. Donaldson, Ross. “Urolithiasis.” WikEM, 13 June 2019, www.wikem.org/wiki/Urolithiasis.
  5. Swaminathan, Anand. “Ureteral Colic.” Core EM, 6 July 2016, coreem.net/core/ureteral-colic.
  6. Bove P, Kaplan D, Dalrymple N, et al: Re-examining the value of hematuria testing in patients with acute flank pain. J Urol 162: 685, 1999.
  7. Zanetti G, Paparella S, Trinchieri A, et al: Infections and urolithiasis: current clinical evidence in prophylaxis and antibiotic therapy. Arch Ital Urol Androl 80: 5, 2008.
  8. Brisbane W, Bailey MR, Sorensen MD. An overview of kidney stone imaging techniques. Nat Rev Urol. 2016;13(11):654–662.
  9. Smith RC, Verga M, Dalrymple NC, et al: Acute ureteral obstruction: value of secondary signs on helical unenhanced CT. AJR Am J Roentgenol 167: 1109, 1996.
  10. Poletti PA, Platon A, Rutschmann OT, et al: Low-dose versus standard-dose CT protocol in patients with clinically suspected renal colic. AJR Am J Roentgenol 188: 927, 2007.
  11. Worster A, Preyra I, Weaver B, Haines T: The accuracy of noncontrast helical computed tomography versus intravenous pyelography in the diagnosis of suspected acute urolithiasis: a meta-analysis. Ann Emerg Med 40: 280, 2002.
  12. Watkins S, Bowra J, Sharma P, et al: Validation of emergency physician ultrasound in diagnosing hydronephrosis in ureteric colic. Emerg Med Australas 19: 188, 2007
  13. Springhart WP, Marguet CG, Sur RL, et al: Forced versus minimal intravenous hydration in the management of acute renal colic: a randomized trial. J Endourol 20: 713, 2006.
  14. Pathan, SA et al. Delivering safe and effective analgesia for management of renal colic in the emergency department: a double blind, multi-group, randomized controlled trial. Lancet. 2016 May 14; 387(10032): 1999-2007.

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