What is the initial management for a patient presenting with flank pain?

Initial Management of Flank Pain

For acute flank pain, immediately obtain non-contrast CT of the abdomen and pelvis as the first-line imaging study, which has 98-100% sensitivity and specificity for detecting urinary stones and identifies alternative diagnoses in approximately one-third of patients. 1, 2, 3

Immediate Assessment and Triage

Critical Red Flags Requiring Urgent Evaluation

• Hemodynamic instability or shock (vital signs showing hypotension, tachycardia) 2
• Fever with flank pain (suggests pyelonephritis, perinephric abscess, or obstructive uropathy with infection) 4
• Inability to urinate or decreased urine output (suggests complete obstruction) 2, 4
• Delayed menses in women of reproductive age (must exclude ectopic pregnancy) 2

Pain Characteristics That Guide Diagnosis

• Classic renal colic: Colicky, wave-like severe pain independent of body position, radiating to groin or genitals with abrupt onset 2
• Musculoskeletal origin: Pain occurring after prolonged static positioning, worsens with movement or palpation 2
• Infectious etiology: Pain that worsens significantly with external flank pressure suggests pyelonephritis rather than uncomplicated stone disease 4

Diagnostic Imaging Strategy

First-Line Imaging: Non-Contrast CT Abdomen/Pelvis

This is the gold standard and should be obtained immediately in most patients. 1, 2, 3

Key advantages:

• Detects stones of any size, location, or composition with 98-100% sensitivity and specificity 1, 2, 3
• Identifies extraurinary causes in one-third of patients (diverticulitis, appendicitis, gynecologic pathology, vascular emergencies) 2, 3
• No contrast agent needed, avoiding nephrotoxicity and allergic reactions 3
• Completed within 5 minutes 3
• Low-dose CT protocols are non-inferior to standard-dose for detecting ureteral stones (92-99% sensitivity) 4

Alternative Imaging in Specific Populations

• Pregnant patients: Ultrasound is first-line to avoid radiation exposure 2
• Patients with strong suspicion for infection (fever, systemic signs): Consider contrast-enhanced CT after initial non-contrast study if infectious complication suspected 4

Ultrasound Limitations

• Only 72% sensitive for large stones (>5 mm) in proximal ureter, 29% sensitive overall for stones of any size 2
• However, absence of hydronephrosis on ultrasound makes larger ureteral stones (>5 mm) less likely (up to 100% sensitive for hydronephrosis) 2

Immediate Pain Management

Provide rapid analgesia within 30 minutes of presentation:

• Diclofenac intramuscular injection is preferred 2
• Reassess pain control within 1 hour 2
• Failure of analgesia after 1 hour mandates immediate hospital admission 2

Initial Laboratory Evaluation

Important caveat: Normal urinalysis does NOT exclude significant urologic pathology:

• Over 20% of patients with confirmed urinary stones may have negative urinalysis 2
• Hematuria (even microscopic) shifts probability toward stone disease 2

Management Based on Imaging Results

If Stone Disease Confirmed

• Stones <5 mm: Typically pass spontaneously; manage outpatient with hydration and pain control 2
• Stones >5 mm or complete obstruction: Urgent urology referral within 7-14 days for consideration of endoscopic intervention 2
• Instruct patient to maintain high fluid intake and strain urine to catch stones 2
• Fast-track radiology follow-up within 7 days if managed outpatient 2

If Fever Present with Stone

This represents a urologic emergency (obstructive pyelonephritis):

• Immediate hospital admission required 4
• Non-contrast CT may show pyelonephritis or perinephric abscess 4
• Consider contrast-enhanced imaging if initial non-contrast CT inconclusive 4

If No Stone Found on CT

• Only 14% require hospitalization and 4% undergo surgical intervention (compared to 41% hospitalization and 22% intervention when non-appendiceal diagnosis made) 2
• CT will identify alternative diagnoses: right colonic diverticulitis, gastroenteritis, inflammatory bowel disease, benign adnexal masses, pelvic congestion syndrome 2

Follow-Up Protocol

• Telephone follow-up 1 hour after initial assessment and analgesia administration 2
• Reassess within 6 months if pain persists or recurs 1
• Avoid continuous cycles of imaging without therapeutic trials between studies 5

Critical Pitfalls to Avoid

• Do not assume all flank pain is kidney-related; positional nature of symptoms distinguishes musculoskeletal from renal causes 2
• Do not delay imaging in young females; consider gynecologic causes (ectopic pregnancy, ovarian torsion) that may require urgent intervention 2
• Do not miss ectopic pregnancy in women with delayed menses presenting with flank pain 2
• Do not assume absence of hematuria excludes stone disease; clinical picture may have evolved 2
• Do not rely on plain radiography (KUB) as initial imaging; it is only 29% sensitive overall for stones 2