What is the appropriate initial evaluation and management for a patient presenting with flank pain, possible hematuria, nausea and vomiting suggestive of a kidney stone without signs of infection?

Initial Management of Suspected Kidney Stone

For a patient presenting with acute flank pain and suspected kidney stone without signs of infection, obtain a non-contrast CT of the abdomen and pelvis as the first-line imaging study, provide rapid analgesia with NSAIDs (diclofenac 75 mg IM preferred) within 30 minutes, and arrange urgent urology follow-up within 7-14 days if intervention is needed. 1, 2

Immediate Clinical Assessment

Key History Elements to Obtain

• Characterize the pain pattern: Classic renal colic presents as severe, colicky, wave-like pain that is independent of body position and radiates to the groin or genitals with abrupt onset 2, 3
• Prior stone history: Recurrence rates reach 40% at 5 years and 50% at 10 years, making previous episodes highly relevant 4, 5
• Family history of stones: This significantly increases likelihood of stone disease and recurrence risk 6, 7
• Timing relative to position: Pain occurring after prolonged static positioning suggests musculoskeletal origin rather than stone disease 2
• Associated symptoms: Nausea, vomiting, dysuria, urinary frequency, and visible hematuria support the diagnosis 7, 5

Critical Red Flags Requiring Immediate Intervention

• Fever, chills, or signs of sepsis: These indicate possible obstructive pyelonephritis requiring immediate hospital admission, IV antibiotics, and urgent decompression via percutaneous nephrostomy or ureteral stent 2, 6
• Hemodynamic instability or shock: Mandates emergent evaluation 2
• Anuria or inability to urinate: Requires urgent assessment for bilateral obstruction 2
• Solitary kidney with obstruction: This is a urologic emergency 2

Initial Laboratory Work-Up

• Urinalysis with microscopy: Check for hematuria, pyuria, bacteriuria, crystals, and casts—though note that over 20% of confirmed stone patients have negative urinalysis 2, 6, 5
• Urine culture: Obtain if infection is suspected (fever, dysuria, pyuria) 2
• Serum creatinine: Essential to assess baseline renal function 2, 6
• Complete blood count: Identifies leukocytosis suggesting infection 2
• Beta-hCG in all women of reproductive age: Must be performed before imaging to exclude ectopic pregnancy 2

Diagnostic Imaging Strategy

First-Line Imaging: Non-Contrast CT

Non-contrast CT of the abdomen and pelvis is the gold standard imaging modality, with 97-100% sensitivity and 96-100% specificity for detecting urinary stones of any size, location, or composition. 1, 2, 6

Key Advantages of Non-Contrast CT

• Identifies alternative diagnoses in approximately one-third of patients presenting with acute flank pain, including appendicitis, diverticulitis, AAA, and gynecologic pathology 1, 2
• Provides critical information for management decisions: Stone size, location, degree of hydronephrosis, and presence of complications 1, 2
• Low-dose CT protocols are non-inferior: Achieve 92-99% sensitivity while markedly reducing radiation exposure and should be used whenever available 2, 6

Alternative Imaging: Ultrasound

When to Use Ultrasound as First-Line

• Pregnant patients: Ultrasound is mandatory as first-line imaging to avoid ionizing radiation 1, 2, 6
• Severe contrast allergy or significant renal insufficiency: When CT contrast may be needed and is contraindicated 2
• Children: Ultrasound is preferred as initial imaging 6

Performance Characteristics of Ultrasound

• Sensitivity for direct stone detection is only 24-57%, particularly poor for stones <5 mm 1, 2
• Excellent for detecting hydronephrosis: Up to 100% sensitive and 90% specific for hydronephrosis, ureterectasis, and perinephric fluid 1, 2
• Absence of hydronephrosis makes stones >5 mm unlikely 1, 2
• Combining ultrasound with plain abdominal radiography (KUB) increases sensitivity to 79-90% for clinically significant stones 1, 2

Critical Pitfall with Ultrasound Timing

Within the first 2 hours of symptom onset, secondary signs of obstruction (hydronephrosis) may not yet be apparent, reducing ultrasound sensitivity—consider repeat imaging if clinical suspicion remains high despite negative initial ultrasound 1, 2

When to Add Contrast-Enhanced Imaging

Reserve contrast-enhanced CT for specific scenarios only, as it adds diagnostic information in just 5-18% of cases and alters management in only 2-3% of patients 2:

• Suspected complicated infection: Fever with systemic symptoms suggesting pyelonephritis or perinephric abscess 2
• Non-contrast CT is nondiagnostic: Difficulty distinguishing stones from phleboliths 2
• Lack of clinical improvement after initial therapy 2

Pain Management

First-Line Analgesia

Administer intramuscular diclofenac 75 mg within 30 minutes of presentation, then reassess pain control at 1 hour. 2

• NSAIDs are preferred over opioids as first-line therapy for renal colic 8, 4
• Failure of analgesia after 1 hour mandates immediate hospital admission 2
• Combination of NSAIDs and opioids may be used for severe pain 8

Avoid This Common Pitfall

Intensive hydration is not currently recommended for acute renal colic, as it does not facilitate stone passage and may worsen pain by increasing hydrostatic pressure 4

Disposition and Follow-Up

Outpatient Management Criteria

Patients may be managed as outpatients if they meet ALL of the following 2, 6:

• No signs of infection (afebrile, no systemic symptoms)
• Adequate pain control achieved within 1 hour
• No evidence of bilateral obstruction or solitary kidney
• Normal or stable renal function
• Stone characteristics favor spontaneous passage (see below)

Outpatient Instructions

• Maintain high fluid intake and strain urine to catch stones for compositional analysis 2, 6
• Telephone follow-up 1 hour after discharge to reassess pain control 2
• Fast-track radiology within 7 days if managed outpatient 2
• Urgent urology appointment within 7-14 days if stone identified requires intervention 2

Medical Expulsive Therapy (MET)

MET is recommended as first-line therapy for uncomplicated distal ureteral stones ≤10 mm in diameter using alpha-blockers or calcium channel blockers to facilitate passage 7, 4

Stone Size and Location: Predicting Spontaneous Passage

Likelihood of Spontaneous Passage

• Stones <5 mm typically pass spontaneously and can be managed conservatively 1, 2
• Larger stones and more proximally located stones are associated with lower rates of spontaneous passage and higher likelihood of requiring intervention 1
• Stones >5 mm or causing complete obstruction may require endoscopic removal via ureteroscopy, percutaneous nephrolithotomy, or shock wave lithotripsy 1, 2

Indications for Immediate Hospital Admission

Admit immediately if any of the following are present 2, 6, 8:

• Fever, chills, or signs of sepsis with obstructing stone
• Failure of pain control after 1 hour of adequate analgesia
• Anuria or bilateral obstruction
• Solitary kidney with obstruction
• Impaired renal function (acute kidney injury)
• Intractable nausea and vomiting preventing oral intake
• Social factors preventing reliable outpatient follow-up

Long-Term Management and Prevention

Stone Analysis

Stone compositional analysis should be performed for all first-time stone formers to guide prevention strategies 6

Metabolic Evaluation Indications

More extensive metabolic evaluation is reserved for high-risk patients 6, 7, 5:

• Recurrent stones (≥2 episodes)
• Bilateral stone disease
• Strong family history of stones
• Age ≤25 years at first presentation
• Children with first episode
• Malabsorption or intestinal disease

Prevention Strategies

Increased fluid intake and dietary interventions can reduce recurrence risk, which otherwise reaches 40% at 5 years 7, 4

Special Population Considerations

Women of Reproductive Age

Do not delay imaging in young women—ectopic pregnancy, ovarian torsion, and pelvic inflammatory disease must be ruled out promptly and can present with flank pain 2

Pregnant Patients

Ultrasound is the mandatory first-line imaging modality to avoid ionizing radiation; if ultrasound is nondiagnostic and clinical suspicion remains high, MRI without gadolinium may be considered 1, 2