Textbook of Urgent Care Medicine, Chapter 29, Flank Pain and Kidney Stones

Published on October 26, 2026

Original author: William Gluckman

Originally published in 2014. Substantially updated and clinically reviewed in 2026 to reflect current evidence, guidelines, and urgent care practice.

INTRODUCTION

Flank pain is a fairly common presenting complaint in the urgent care setting. Causes may be related to musculoskeletal injury, retroperitoneal injury or organ problems, or thoracic pathology, or be related to a number of intra-abdominal problems. As with most diagnoses, a good history and physical exam will be important in identifying the underlying cause.

The first decision is not whether a stone is present, but whether there is infection, impaired renal drainage, vascular disease, or another serious cause that requires emergency evaluation. Urinalysis and symptom relief do not, by themselves, establish a safe disposition. [1,2]

PRESENTATION

• Back pain
• Pain may radiate to the shoulder, lower abdomen, groin, and genitalia.
• Flank pain is often associated with nausea and/or vomiting.

Sudden severe flank pain radiating toward the groin is suggestive of ureteral colic. Fever, rigors, persistent vomiting, oliguria, syncope, or chest symptoms warrant consideration of an alternative or complicated diagnosis.

TRIAGE PEARLS

• Fever
• Persistent vomiting
• Chest pain
• Shortness of breath
• Tachycardia
• Hypotensive
• Extremity weakness
• Elderly
• Record complete vital signs and assess pain, hydration, mental status, and ability to pass urine. A patient with hypotension, altered mental status, signs of sepsis, or possible abdominal aortic aneurysm (AAA) requires EMS transfer. [1,3]
• Fever or systemic illness together with suspected ureteral obstruction represents a potential infected, obstructed kidney. Arrange immediate ED evaluation for antibiotics, imaging, and possible urinary drainage. Do not manage this combination with outpatient antibiotics alone. [1]
• Also expedite evaluation for a solitary kidney, known advanced kidney disease, anuria, pregnancy with significant flank pain, or uncontrolled pain or vomiting. [1,2]

HISTORY PEARLS

• History of prior renal colic may be helpful.
• History of recent trauma or prior back injury
• History of hypertension, hypercholesterolemia, or atrial fibrillation
• Past surgical history (e.g., cholecystectomy)
• History of gout may suggest uric acid stone formation; a history of stones, prior stone analysis, recurrent infection, and family history better define stone risk.
• History of any recent surgical procedures involving the ureters or aorta:
  • Ureteroscopy
  • Angiography
  • Renal biopsy
  • Cardiac catheterization or ablation
• Onset of pain, sudden versus slow
  • Sudden onset can imply renal colic, biliary colic, intestinal gas pain, AAA, renal infarction, or hemorrhagic adrenal mass.
  • Slow onset can imply pyelonephritis, renal abscess, pneumonia, pleural effusion, or renal mass.
• Pain that radiates to the ipsilateral scrotum or labia is likely due to a ureteral stone.
• Pain that changes with position can favor a musculoskeletal source, but position, restlessness, or pain quality cannot reliably exclude a ureteral stone or a dangerous alternative.
• Urinary symptoms:
  • Frequency
  • Urgency
  • Dysuria
  • Blood clots
• Associated symptoms:
  • Fever
  • Vomiting
  • Cough
  • Chest pain
  • Shortness of breath
• Ask about reduced urine output, previous kidney function, anticoagulant use, pregnancy possibility, and urinary tract instrumentation. In older adults, inquire about known aneurysm; with atrial fibrillation or recent vascular procedures, consider renal infarction. [2,9]

PHYSICAL EXAM PEARLS

• How does the patient look?
  • Are they comfortable?
  • Are they toxic? Are they writhing around and cannot assume a position of comfort, or do they lie still?
• Costovertebral angle tenderness may be present in hydronephrosis or pyelonephritis and thus is a nonspecific finding.
• Musculoskeletal back pain typically has an associated mechanism of injury but may occur from a seemingly minor event. Pain with range of motion and palpatory tenderness and/or muscle spasm are often present.
• Lung auscultation should be performed for evidence of pneumonia or pleural effusion.
• Cardiac exam
  • May reveal tachycardia, which is nonspecific and may be secondary to pain, but may represent early sepsis from infection or hypovolemia from bleeding.
  • Assess rhythm when embolic renal infarction is a concern; atrial fibrillation materially changes the differential diagnosis.
• Abdominal exam
  • An abdominal exam may reveal tenderness in the presence of a stone even though the kidneys and ureters are retroperitoneal.
  • A palpable pulsatile mass is likely an AAA.
  • Rebound tenderness is a sign of peritonitis and should not be seen with kidney stones but may be present in the face of acute cholecystitis, appendicitis, or diverticulitis/colitis or when free fluid is in the abdomen (as with a ruptured ovarian cyst or ectopic pregnancy).
  • The absence of a palpable mass does not exclude AAA, especially in obesity. Assess perfusion and femoral pulses when vascular disease is suspected.
• Skin exam:
  • The presence of lesions is consistent with shingles.
  • Flank ecchymosis, also known as Grey Turner sign, may be present in the face of acute hemorrhagic pancreatitis.
  • Pale skin may be present if the patient is anemic secondary to blood loss.
  • Jaundice may be present in hepatitis either primary or secondary to obstruction (pancreatic mass).
• Perform genital or pelvic examination when indicated by symptoms. Testicular torsion, ovarian torsion, and ectopic pregnancy can present with misleading lower abdominal or flank pain; suspected torsion or ectopic pregnancy needs immediate emergency evaluation.

TESTING PEARLS

• Urinalysis is a fast, easy, and noninvasive screening tool:
  • Presence of only red blood cells is less likely to represent infection.
  • Normal findings on urinalysis do not exclude infection or stones.
  • Hematuria supports but does not confirm stone disease; absence of hematuria does not rule it out. Pyuria or nitrites should prompt assessment for infection, particularly when there are fever or systemic symptoms. [1,2]
• Obtain urine culture if pyelonephritis or an infected stone is suspected; cultures are not routinely needed for uncomplicated renal colic without infection. [1,7]
• Blood work:
  • Check creatinine/eGFR and electrolytes when renal impairment, dehydration, bilateral disease, a solitary kidney, infection, or contrast-enhanced imaging is being considered. CBC may help evaluate systemic infection or bleeding but neither normal CBC nor normal renal function excludes serious disease.
  • Amylase and lipase tests can help rule in pancreatitis.
• Urine pregnancy testing should be performed on all women of childbearing age because ectopic pregnancy can have an atypical presentation of flank pain.
• Traditional x-ray study is of limited utility:
  • Plain kidney-ureter-bladder radiography may miss small stones and radiolucent stones; it is not sufficient to rule out obstruction or alternative emergencies. Its main role is selected follow-up of known radiopaque stones. [2]
• CT scan without contrast is a better exam study if kidney stones or ureterolithiasis is suspected:
  • Demonstrates the location of the stone within the urinary tract.
  • Demonstrates its size.
  • Demonstrates presence or absence of hydronephrosis.
  • Low-dose noncontrast CT of the abdomen and pelvis is generally preferred when definitive imaging for a suspected stone is needed in a nonpregnant adult. It detects many alternative causes, but noncontrast CT must not be assumed to exclude aortic catastrophe or renal infarction. [2,3,9]
• Ultrasound is a good screening tool for young women because there is no ionizing radiation and the scan can identify hydronephrosis and stones in the kidney and upper ureter.
• Ultrasound is the preferred initial imaging test during pregnancy. A negative or nondiagnostic ultrasound does not exclude ureteral obstruction; further imaging and obstetric/urologic evaluation may be necessary. [2,3]

Finding or circumstance	Best urgent care next step
First-time suspected stone; imaging needed	Arrange timely low-dose noncontrast CT. Escalate to ED if severe symptoms, uncertain diagnosis, or timely imaging is not possible.
Pregnancy with possible renal colic	Pregnancy test if status unknown; ultrasound first. Arrange urgent obstetric/ED assessment if fever, severe pain, or obstruction is suspected.
Fever/rigors with possible obstruction	ED immediately; urgent decompression may be necessary. Do not delay transfer for outpatient imaging.
Abrupt pain with vascular risk, syncope, or concerning perfusion	EMS/ED for evaluation of AAA, dissection, or renal infarction; vascular imaging may require IV contrast.
Simple recurrent colic, stable and previously confirmed stones	Select imaging by change in symptoms, radiation exposure, follow-up needs, and access; do not assume an identical cause.

DIAGNOSIS PEARLS

Renal colic

• Renal colic often has rapid onset and severe pain; positional behavior is suggestive but not diagnostic.
• Hematuria is common but may be absent.
• Ultrasound is a good screen to check for intrarenal stones and to evaluate for hydronephrosis but noncontrast CT of the abdomen and pelvis provides more information.
• Stone location, size, obstruction, symptoms, and infection findings together determine whether observation is appropriate. Small distal stones often pass spontaneously; passage is less likely as size increases. [1,5]

Biliary colic

• Pain typically comes and goes.
• Is usually associated with or exacerbated by food
• Nausea/vomiting and right upper quadrant tenderness are present.
• Ultrasound is the diagnostic study of choice.
• Fever, jaundice, persistent right upper quadrant tenderness, or systemic illness requires evaluation for cholecystitis/cholangitis and possible hospital transfer.

Intestinal gas pain

• This benign disorder can be painful and mimic other entities presented in this chapter. It is more of a diagnosis of exclusion, but pain that is sharp, crampy, and characterized by periods of complete relief from pain is typical.
• Care should be taken to rule out intestinal obstruction, in particular in older patients and those with a history of prior abdominal surgery.

Abdominal aortic aneurysm (AAA)

• This disorder does not always present with typical pain and a pulsatile mass.
• Palpation of a pulsatile mass is difficult in obese patients.
• Vague achy or tearing pain radiating to the back is common.
• Rapid transfer to an emergency department with vascular surgery capabilities is critical if AAA is suspected.
• Unstable patients will likely demonstrate tachycardia and other signs of shock such as delayed capillary refill and may be hypotensive.
• A normal abdominal examination or absence of a palpable mass cannot safely rule out AAA. Bedside ultrasound may support the diagnosis where available, but must not delay EMS transfer. Stable patients may require CT angiography at the receiving hospital. [3]

Herpes zoster (before lesions appear)

• Herpes zoster can present with pain and lesions essentially following any nerve root dermatome. The discomfort (either itching, burning, or pain) may present a few days before the typical diagnostic skin lesions appear.
• Early antivirals are most effective when started promptly after onset of the characteristic rash; the decision depends on timing, distribution, age, and immune status.

Renal infarction

• This is fortunately rare but is reportedly underdiagnosed.
• Hematuria is common but not always present.
• Sudden unexplained flank pain with atrial fibrillation, embolic risk, or recent vascular instrumentation should raise concern for renal infarction. Noncontrast stone-protocol CT may be negative; contrast-enhanced CT/CT angiography is ordinarily needed in the ED. Early recognition can preserve renal function. [9]

Pyelonephritis

• This infection of the kidneys presents with flank and/or upper abdominal pain and is often associated with fever/chills and urinary symptoms.
• A urinalysis often reveals an elevated white blood cell count and bacteria and may demonstrate white blood cell casts or red blood cells.
• Stable, nonpregnant patients without suspected obstruction, sepsis, severe comorbidity, or inability to take oral therapy may be treated as outpatients when follow-up is reliable. Obtain a urine culture before antibiotics when feasible and adjust treatment to susceptibility. [7]
• Nitrofurantoin should not be used to treat pyelonephritis.
• Antibiotic choice and duration should follow current local resistance and culture results. For clinically improving adults with complicated UTI, including selected cases of pyelonephritis, 5–7 days of an effective fluoroquinolone or 7 days of an effective non-fluoroquinolone can be appropriate; patients with abscess, obstruction, severe immunosuppression, or other complicating factors may need individualized longer treatment. [7]

Renal abscess

• Renal abscess may be difficult to differentiate from acute pyelonephritis and presents with fever, flank pain, abdominal pain with frequent urination, and/or dysuria.
• Consider an abscess when presumed pyelonephritis does not improve promptly or when stone, obstruction, diabetes, or other risk factors are present. Cross-sectional imaging, IV antimicrobials, and possible drainage require hospital evaluation. [1,7]

Pneumonia and pleural effusion

• Pneumonia, especially when in the lower lobes, may present with flank pain. Careful attention to a history of cough, shortness of breath, fever and chest pain along with abnormal lung auscultatory findings should help lead to this diagnosis.
• Like pneumonia, a pleural effusion may cause irritation and be perceived as a sensation of flank pain by a patient.
• Consider chest radiography when pulmonary findings support these diagnoses; evaluate hypoxemia or severe respiratory distress in an ED.

Renal mass and hemorrhagic adrenal mass

• Typically, these are incidental findings found on a CT scan or ultrasound done to evaluate other problems.
• Hemorrhage within the adrenal glands can be life-threatening if not identified and treated.
• Unexpected mass, significant hematuria, persistent pain, hypotension, or concern for hemorrhage warrants imaging and specialty evaluation based on severity.

TREATMENT AND DISPOSITION PEARLS

• Pain should be managed aggressively. The following is a suggested list of treatment options for pain:
  • NSAIDs:
    • Ketorolac
    • Naproxen sodium
    • Ibuprofen
• NSAIDs are preferred first-line therapy for suspected renal colic when there is no significant kidney injury, dehydration, active GI bleeding, relevant hypersensitivity, high cardiovascular risk, or pregnancy-related contraindication. Use the lowest effective dose for a short course; avoid combining different NSAIDs. [1,4,8]
• Acetaminophen is a reasonable alternative or adjunct when NSAIDs cannot be used. Opioids should be limited to selected patients with persistent severe pain after other options, with attention to sedation and safety. [1,4]
• Antiemetics, which may be useful adjuncts:
  • Ondansetron
  • Metoclopramide
• Hydrate patients who are volume depleted or unable to maintain oral intake. Forced IV fluids solely to hasten stone passage are not recommended. [5]
• For an imaging-confirmed distal ureteral stone 5–10 mm, a trial of an alpha-blocker (for example, tamsulosin 0.4 mg orally once daily for up to 4 weeks) may be considered if infection, significant obstruction, renal impairment, and other reasons for urgent intervention have been excluded. This is off-label; discuss dizziness and orthostatic hypotension. [1,5]
• Some stones may require urgent urologic intervention. Fever or infection with obstruction, sepsis, anuria, acute kidney injury, a solitary kidney with threatened drainage, or uncontrolled symptoms warrants emergency assessment. [1]
• Potassium citrate or other urine alkalinization is not a routine acute-colic intervention or a treatment for all stones. Stone composition and a metabolic evaluation guide prevention; urinary alkalinization may be appropriate for selected uric acid or hypocitraturic stone formers under longitudinal care. [6]
• For patients with pyelonephritis, use antibiotics active against likely urinary pathogens and obtain cultures where indicated; urgent hospital care is needed when sepsis, infected obstruction, pregnancy with systemic illness, inability to tolerate oral treatment, or other high-risk features are present. [7]

Clinical status	Disposition
Shock, syncope, suspected AAA/dissection, renal infarction, or severe systemic illness	EMS transfer to an emergency department; do not delay for outpatient CT or laboratory tests.
Fever/rigors or systemic UTI with suspected obstruction; anuria; solitary kidney with obstruction; AKI	Emergency department and urgent urologic assessment; possible decompression and IV antibiotics.
Persistent severe pain, recurrent vomiting, inability to drink, diagnostic uncertainty, or pregnancy with significant symptoms	Same-day ED evaluation; assess imaging needs and hydration/renal function.
Stable, nonpregnant patient; established uncomplicated small ureteral stone; controlled pain; no infection or renal compromise	Outpatient treatment can be reasonable with timely imaging or imaging review, urology/primary-care follow-up, and confirmation of resolution or passage.
Persistent symptoms or no documented stone passage	Reassess promptly, including repeat imaging as indicated; prolonged obstruction cannot be excluded from symptom improvement alone.

MEDICOLEGAL PEARLS

• Testicular torsion can present as flank pain. Document lack of any testicular findings.
• An aortic emergency can present with flank pain, sometimes without a palpable mass or dramatic hypotension. Document the differential diagnosis and transfer decision; do not use a normal abdominal examination alone to exclude it.
• A patient with abrupt, unexplained pain and embolic risk factors needs consideration of renal infarction even if the urinalysis and noncontrast CT are unrevealing. [9]
• The presence of fever or abnormal vital signs in a patient thought to have renal colic should prompt evaluation for infected obstruction. Delayed drainage is a preventable cause of severe harm. [1]
• Document the limits of onsite imaging and laboratory testing, important negative findings, response to analgesia, and the follow-up pathway. Persistent pain or inability to confirm stone passage warrants reevaluation well before an arbitrary 5-day waiting period. [2,5]

REFERENCES

1. European Association of Urology. EAU Guidelines on Urolithiasis. 2026. Source
2. Gupta RT, Kalisz K, Khatri G, et al. ACR Appropriateness Criteria: Acute Onset Flank Pain—Suspicion of Stone Disease (Urolithiasis). J Am Coll Radiol. 2023;20(11 suppl):S315-S328. doi:10.1016/j.jacr.2023.08.020. Source
3. American College of Radiology; RadiologyInfo.org. Acute Onset Flank Pain—Suspicion of Stone Disease (Urolithiasis). Reviewed January 23, 2024. Source
4. National Institute for Health and Care Excellence. Renal and Ureteric Stones: Assessment and Management. NICE guideline NG118. 2019. Source
5. Canadian Urological Association. Management of ureteral calculi: abridged guideline. Can Urol Assoc J. 2021. Source
6. Pearle MS, Matlaga BR, Antonelli JA, et al. Medical Management of Kidney Stones: AUA Guideline (2026), Parts I and II. J Urol. Published online July 30, 2026. doi:10.1097/JU.0000000000005227 and 10.1097/JU.0000000000005228. Source
7. Infectious Diseases Society of America. Clinical Practice Guidelines on Management and Treatment of Complicated Urinary Tract Infections: Duration of Antibiotics. 2025. Source
8. US Food and Drug Administration. FDA Recommends Avoiding Use of NSAIDs in Pregnancy at 20 Weeks or Later Because They Can Result in Low Amniotic Fluid. Updated September 1, 2022. Source
9. Saju JMM, Leslie SW. Renal Infarction. StatPearls. Updated March 10, 2024. Source