Non-Contrast CT of the Abdomen and Pelvis
For a patient with left flank pain and hematuria in a primary care clinic, order a non-contrast CT of the abdomen and pelvis immediately—this is the gold-standard imaging study with 98-100% sensitivity and specificity for detecting urinary stones and will identify alternative diagnoses in approximately one-third of patients. 1
Why Non-Contrast CT Is the Correct Choice
Non-contrast helical CT has replaced intravenous urography as the imaging modality of choice for acute flank pain with hematuria, demonstrating superior diagnostic accuracy with 97-99% sensitivity and 92-97% specificity for detecting ureteral calculi 2, 3, 4
The combination of flank pain and hematuria most commonly indicates urolithiasis, making non-contrast CT the appropriate first-line study 5
This single examination evaluates the entire urinary tract—kidneys, ureters, and bladder—and detects stones of any size, location, or composition without requiring intravenous contrast 2, 6
Critical Advantages Over Other Modalities
Speed and availability: Non-contrast CT provides rapid diagnosis (typically within minutes), allowing faster emergency department turnover and more timely clinical decision-making compared to traditional excretory urography 2
Detection of alternative pathology: In patients without stone disease, CT identifies non-urologic causes of flank pain in 30-32% of cases, including appendicitis, diverticulitis, ovarian pathology, and vascular emergencies 4, 6
No contrast complications: By avoiding intravenous contrast, you eliminate risks of contrast-induced nephropathy and allergic reactions while reducing cost 2, 3
When Ultrasound Is NOT Appropriate Here
Although ultrasound is recommended as first-line imaging in pregnant patients to avoid radiation 5, 1, your patient's pregnancy status is not mentioned, so standard adult protocols apply
Ultrasound has only 24-57% sensitivity for direct stone visualization (especially stones <5 mm) and may miss obstruction entirely in the first 2 hours of symptom onset 1
The absence of hydronephrosis on ultrasound makes larger stones (>5 mm) less likely, but does not exclude clinically significant stone disease 5, 1
Low-Dose CT Protocols
- If available at your facility, request a low-dose CT protocol, which maintains 92-99% sensitivity for stone detection while significantly reducing radiation exposure 1
What to Expect from the CT Report
The radiologist will document stone size, location, degree of hydronephrosis, and presence of perinephric or periureteral stranding 2
Stones <5 mm typically pass spontaneously, while larger stones or those causing complete obstruction may require urologic intervention 5, 1
If no stone is identified, the report should describe any alternative intra-abdominal findings that explain the symptoms 4, 6
Common Pitfalls to Avoid
Do not order a contrast-enhanced CT initially—while contrast studies can safely exclude obstruction (negative predictive value 100%), they add unnecessary cost and risk when non-contrast CT is diagnostic in the vast majority of cases 7
Do not start with plain radiography (KUB)—sensitivity is only 29% overall and 72% for large proximal stones, making it inadequate for ruling out stone disease 5, 1
Do not assume absence of hematuria excludes stones—more than 20% of patients with confirmed urolithiasis have negative urinalysis 1
Urgent Referral Criteria After Imaging
If CT confirms a stone with fever, signs of infection, or inability to control pain, arrange same-day urology consultation for possible urgent intervention 5, 1
Stones >5 mm, complete obstruction, or solitary kidney with obstruction require urgent urology referral within 7-14 days 5, 1
If the patient develops hemodynamic instability or signs of sepsis, immediate hospital admission is required regardless of imaging results 5, 1