Name: Flank pain — bulletproof documentation — ER Toolkit
Creator: Kim Trinh, MD

"Looks like a kidney stone" is the most dangerous sentence in flank pain. At least half of patients with acute flank pain have no stone on CT, and a meaningful fraction have a serious alternative — including a leaking aneurysm. The chart should show you considered the catastrophic mimics before you settled on colic.

01What's at stake

At triage, a patient with flank pain "may have a calculus, or it could be an AAA awaiting rupture." In one series of stone-protocol CTs, 27% had a significant alternative diagnosis — cholelithiasis, appendicitis, pyelonephritis, ovarian cyst, renal mass, and AAA (with and without rupture, ~1.4%). Misdiagnosing an older patient's leaking aneurysm or an infected obstructing stone as simple colic is the high-liability miss.

02Can't-miss differential

Abdominal aortic aneurysm / dissection — older, vasculopath, first-time "stone," syncope; bedside US and unenhanced CT have limits for dissection and contained leak.
Infected obstructing stone / pyonephrosis — fever + obstruction is a urologic emergency needing decompression.
Renal infarction / renal vein thrombosis — AFib, hypercoagulable; persistent pain with a "negative" stone CT.
Testicular / ovarian torsion, ectopic — GU emergencies that mimic colic.
Appendicitis — retrocecal appendix can present as right flank pain.

03History & exam

First episode, or age >50 with vascular risk? → image for AAA
Fever, rigors, looks toxic? → infected obstructing stone
Hypotension, syncope, altered mentation? → AAA / urosepsis
Significant abdominal tenderness, rebound, or guarding? → not just colic — investigate
Palpate the aorta for tenderness/pulsatile mass; examine the genitals — torsion mimics colic even with "prior similar pain."

Skip the typing

Work it up in the Flank Pain Workup — it records the urinalysis, pregnancy test, and imaging decision, and assembles an MDM that documents AAA, infection, and torsion were considered before landing on renal colic.

04Testing — and why the dipstick lies

Hematuria is unreliable. Microscopic hematuria is ~84% sensitive / ~48% specific for stone — its absence does not exclude a stone, and its presence does not confirm one (AAA, infection, and menses all cause it).
Non-contrast CT is the diagnostic modality of choice (sensitivity 94%–100%) and detects most alternatives; a first episode or an unclear diagnosis warrants CT rather than imaging-free discharge.
Ultrasound first in pregnancy and children to limit radiation; it can miss stones, so a negative US with persistent pain is not the end.
Look for the infected obstruction — temperature (rectal in the elderly if needed), urinalysis for pyuria, WBC; fever + obstruction → antibiotics, imaging, urology, admission.
Analgesia — NSAIDs (e.g., ketorolac) ± an opioid; the combination beats either alone.

05What to document

▼ weak

"Flank pain, blood on dip. Renal colic. Pain better with toradol, discharged."

▲ defensible

"Colicky flank pain radiating to groin, restless; afebrile, soft non-tender abdomen, aorta non-tender without pulsatile mass, normal genital exam. Not a first stone; no vascular risk features. Non-contrast CT: 4-mm obstructing stone, no AAA or alternative pathology, no hydronephrosis suggesting infection. AAA, infected obstruction, and torsion considered and excluded. Return for fever/chills, intractable pain, persistent vomiting, or inability to urinate."

06Where charts fail

Diagnosing colic off a urine dipstick — present or absent blood proves nothing.
Calling an older first-time "stone" benign without imaging for AAA.
Missing fever in the elderly stone patient — urosepsis decompensates fast.
Skipping the genital exam in a patient who "knows it's a stone."
Discharging a >7-mm stone without urology follow-up.

07Sources

Carter MR, Green BR. Renal calculi: emergency department diagnosis and treatment. Emergency Medicine Practice (EB Medicine). 2011;13(7).
Koroglu M, Wendel JD, Ernst RD, et al. Alternative diagnoses to stone disease on unenhanced CT for acute flank pain. Emerg Radiol. 2004;10:327-333.
Luchs JS, Katz DS, Lane MJ, et al. Utility of hematuria testing in suspected renal colic: correlation with unenhanced CT. Urology. 2002;59:839-842.
Safdar B, Degutis LC, Landry K, et al. IV morphine plus ketorolac is superior to either drug alone for acute renal colic. Ann Emerg Med. 2006;48(2):173-181.

Flank pain: documentation that holds up