Flank Pain / Renal Colic

Key considerations: Ruptured AAA (mimics renal colic), Pyelonephritis with sepsis, Obstructing stone with solitary kidney

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history: Location and radiation: classic flank → groin radiation with renal colic; Colicky vs constant (colicky = stone, constant = pyelonephritis); Hematuria (blood in urine); Dysuria, frequency, urgency (UTI/pyelonephritis); Prior kidney stones, family history; Nausea, vomiting (vagal response to ureteral distension); exam: CVA tenderness (pyelonephritis); Abdominal exam: rule out peritoneal signs; Testicular exam: torsion can present as flank/abdominal pain; Vital signs: fever (infection), tachycardia (pain or sepsis); Pulsatile abdominal mass (AAA — especially in elderly with first-time flank pain); labs: Urinalysis: hematuria (90% of stones), pyuria, nitrites, bacteria; CBC: WBC if infection suspected; BMP: creatinine (obstructive AKI), BUN; Urine culture if UTI/pyelonephritis; HCG in women of reproductive age; Lactate if sepsis suspected; imaging: CT abdomen/pelvis non-contrast (stone protocol): gold standard for nephrolithiasis; Renal ultrasound: first-line in pregnancy and pediatrics — detects hydronephrosis; KUB: limited utility — only shows radiopaque stones; bedside: Point-of-care renal ultrasound: hydronephrosis; Pregnancy test; Aorta ultrasound if >50 years with new-onset flank pain (rule out AAA)

immediate: Pain control: ketorolac 30mg IV (first-line for renal colic — proven superior to opioids); IV fluids: moderate hydration (aggressive hydration does not hasten stone passage); Antiemetics: ondansetron for nausea; general: Stone size determines management: <5mm → 90% pass spontaneously; 5-10mm → 50%; >10mm → unlikely to pass; Medical expulsive therapy: tamsulosin 0.4mg daily (for stones 5-10mm — relaxes ureteral smooth muscle); Strain urine for stone analysis; specific: diagnosis: Uncomplicated Stone <10mm; steps: Pain control and antiemetics; Tamsulosin 0.4mg daily x4 weeks; Urology follow-up in 1-2 weeks; Return if fever, uncontrolled pain, or vomiting; diagnosis: Infected Obstructing Stone; steps: UROLOGIC EMERGENCY — emergent decompression required; IV antibiotics (ceftriaxone or piperacillin-tazobactam); Urology consult for emergent ureteral stent or percutaneous nephrostomy; This is sepsis source control — time-critical; diagnosis: Pyelonephritis; steps: Urine and blood cultures; IV antibiotics: ceftriaxone 1g IV or ciprofloxacin 400mg IV; CT abdomen if not improving after 48-72 hours (abscess, obstruction); Transition to PO antibiotics when afebrile and improving

admit: Infected obstructing stone (urologic emergency); Intractable pain or vomiting; Acute kidney injury from obstruction; Solitary kidney with obstruction; Pyelonephritis with sepsis or inability to tolerate PO; Stone >10mm requiring intervention; discharge: Stone <10mm with controlled pain; Able to tolerate PO fluids and medications; Tamsulosin prescribed, strainer provided; Urology follow-up in 1-2 weeks; Clear return precautions: fever, severe pain, unable to urinate; consults: Urology: stones >10mm, infected obstruction, failed conservative management, bilateral obstruction; IR: percutaneous nephrostomy if urology unavailable

Ketorolac is FIRST-LINE for renal colic pain — superior to opioids in randomized trials and does not cause nausea
Elderly patient with first-time "renal colic" = consider AAA — bedside aorta ultrasound takes 30 seconds
Infected obstructing stone = urologic emergency. Antibiotics alone will not treat this — the obstruction must be decompressed
Stone size is the best predictor of passage: <5mm = 90% pass, >10mm = almost never passes spontaneously
Tamsulosin benefit is modest and mainly for stones 5-10mm — NNT ~4 for facilitating passage

AUA/EAU Urolithiasis Guidelines 2022, ACEP Renal Colic Clinical Policy. Last reviewed: 2024-11-01