What investigations should be ordered for a patient with abdominal pain and vomiting, and a previous history of ureteric (urinary tract) calculi (kidney stones)?

Investigations for Abdominal Pain and Vomiting with Prior Ureteric Calculi History

Order non-contrast CT abdomen and pelvis as the primary investigation, supplemented by urinalysis, complete blood count, serum creatinine, and CRP to assess for infection and renal function. 1, 2

Imaging Strategy

Primary Investigation: Non-Contrast CT Abdomen and Pelvis

Non-contrast CT is the gold-standard investigation for patients with suspected recurrent stone disease, providing near-perfect accuracy for stone detection, size, location, density, and degree of hydronephrosis. 1, 2 This modality is particularly critical given the patient's prior stone history, as it:

• Detects stones with superior sensitivity and specificity compared to all other modalities 1, 2
• Identifies stone size, location, and density to guide treatment decisions 3, 2
• Assesses for hydronephrosis and degree of obstruction 1
• Detects alternative diagnoses that may explain abdominal pain and vomiting, including cholecystitis, appendicitis, and liver abscess 1
• Provides information about stone passage likelihood based on stone characteristics 2

The nephrographic phase alone (contrast-enhanced CT) has 90-92% accuracy for diagnosing both acute pyelonephritis and urolithiasis (96-99% accuracy), making additional unenhanced phases unnecessary in most cases. 1 However, in patients with known stone history, non-contrast CT remains preferred as the initial study. 1

Alternative Initial Approach: Point-of-Care Ultrasound

If immediate CT is unavailable or radiation exposure is a concern, point-of-care ultrasound can serve as an initial investigation, particularly in moderate-to-high risk patients with typical renal colic presentation. 4, 2

• Moderate-to-severe hydronephrosis on ultrasound is highly specific (94.4%) for symptomatic renal stone and may be sufficient for treatment decisions without CT 4
• Any degree of hydronephrosis increases positive predictive value to 88% for ureteral stones 4
• Critical pitfall: Absence of hydronephrosis does NOT rule out ureteric colic—negative predictive value is only 65-87% 4, 2
• Ultrasound has only 54% sensitivity for stone detection and significantly overestimates stone size in the 0-10mm range 3, 2

If ultrasound shows moderate-to-severe hydronephrosis in a patient with high clinical probability of stone disease, proceed with conservative management or urology consultation; if no hydronephrosis or diagnosis uncertain, CT is mandatory. 4

Essential Laboratory Investigations

Infection Assessment (Highest Priority)

Check for signs of infected obstructed kidney, which constitutes a urological emergency requiring immediate decompression within hours: 3, 2

• Complete blood count to assess for leukocytosis indicating infection 2
• C-reactive protein (CRP) as infection marker 3
• Urine dipstick and urinalysis for pyuria, bacteriuria, and hematuria 3, 2
• Blood cultures if fever present to rule out urosepsis 2

The combination of fever with obstruction mandates emergent percutaneous nephrostomy—this is a urological emergency. 3, 2

Renal Function Assessment

• Serum creatinine to assess baseline renal function, particularly critical given prior stone history 3
• Document any decline in renal function compared to baseline 3

Urinalysis Findings

• Hematuria supports diagnosis but absence does NOT exclude stones—up to 20-80% of stone patients may lack hematuria 2, 5
• Combined absence of hydronephrosis and hematuria has 96.4% negative predictive value for ureteral stone 1

Risk Stratification Based on Findings

High-Risk Features Requiring Urgent Urology Consultation

Immediate urology consultation is required if any of the following are present: 3, 2

• Fever with obstruction (signs of infected obstructed kidney) 3, 2
• Sepsis indicators: hypotension, tachycardia, altered mental status 3
• Moderate-to-severe hydronephrosis (97% sensitivity for requiring urological intervention) 3
• Intractable pain unresponsive to NSAIDs 2
• Stone >10mm unlikely to pass spontaneously 2
• Solitary kidney with obstruction 3

Moderate-Risk Features

Patients with moderate hydronephrosis are at significantly higher risk of stone passage failure and require close monitoring: 1, 3

• Moderate hydronephrosis predicts need for intervention with high likelihood 3
• These patients benefit from CT imaging to determine exact stone size, location, and density for treatment planning 3
• Medical expulsive therapy may be attempted but stones should pass within 28 days or intervention is indicated 2

Common Diagnostic Pitfalls to Avoid

Do not assume absence of hydronephrosis rules out significant stones—this has only 65% negative predictive value and cannot exclude stone disease. 1, 4

Do not rely solely on ultrasound for treatment decisions when CT is available—ultrasound has only 54% sensitivity and significantly overestimates stone size. 3, 2

Do not delay drainage if infection is present with obstruction—this constitutes a urological emergency requiring percutaneous nephrostomy within hours, not days. 3, 2

Do not order KUB radiography as initial investigation—it is not beneficial for initial evaluation and has inferior sensitivity compared to CT. 1

Do not assume all small stones will pass spontaneously—presence of moderate-to-severe hydronephrosis indicates higher risk of passage failure even with stones <5mm. 2

Pain Management During Investigation

Administer intramuscular diclofenac as first-line analgesia to provide rapid pain relief and reduce smooth muscle spasm—NSAIDs are superior to opioids for renal colic pain. 2