Flank Pain Without Pyuria or CVA Tenderness: Next Diagnostic Step
Order a CT abdomen and pelvis WITH intravenous contrast rather than the standard non-contrast "stone protocol" CT, as the absence of pyuria and negative CVA tenderness significantly reduces the likelihood of urolithiasis and increases the probability of alternative diagnoses that require contrast for proper characterization. 1, 2, 3
Clinical Reasoning
The absence of both pyuria and CVA tenderness fundamentally changes your diagnostic approach:
- Pyuria is typically present with urinary tract pathology regardless of location (cystitis, pyelonephritis, or obstructing stones), and its absence suggests an alternative non-urological etiology 4
- Negative CVA tenderness further reduces the likelihood of acute pyelonephritis or symptomatic urolithiasis 4
- Combined negative urinalysis (no pyuria) and no history of urolithiasis has a 94% sensitivity for detecting calculi, meaning only 6% of stone cases would be missed by this screening approach 3
Evidence-Based Imaging Strategy
Why Contrast-Enhanced CT is Superior in This Scenario
- In patients with flank pain, negative urinalysis, and no history of urolithiasis, 15% have alternative diagnoses that are optimally characterized with IV contrast 3
- Contrast-enhanced CT provides a 96% rate of optimal diagnosis compared to 85% with non-contrast CT in this specific patient subset (p = .03) 3
- Non-contrast "stone protocol" CT limits diagnostic utility for non-urological causes of flank pain, which become the primary concern when pyuria is absent 1
Alternative Diagnoses to Consider
When flank pain presents without pyuria or CVA tenderness, contrast-enhanced imaging better evaluates:
- Appendicitis (particularly retrocecal appendix presenting with right flank pain) 1
- Acute focal bacterial nephritis (can present with fever and flank pain without pyuria or positive cultures) 5
- Vascular pathology (renal infarction, renal vein thrombosis) 1
- Gynecological pathology (ovarian torsion, tubo-ovarian abscess) 1
- Other intra-abdominal processes (diverticulitis, bowel obstruction) 1, 6
Important Caveats
Risk of Missing Small Stones
- Only 4% of patients with negative history and negative urinalysis had non-obstructing 1-2 mm calculi that could potentially be obscured by contrast 3
- These tiny stones are typically clinically insignificant and non-obstructing, making the trade-off acceptable given the 15% rate of alternative diagnoses requiring contrast characterization 3
When Non-Contrast CT Remains Appropriate
If clinical suspicion for stones remains high despite negative pyuria (e.g., patient has classic renal colic with radiation to groin, previous stone history), consider:
- Starting with non-contrast CT, then adding contrast-enhanced phases if initial study is inconclusive 1
- This sequential approach identified additional diagnoses or provided new information in 5-18% of cases, though it changed management in only 2-3% 1
Clinical Pitfall to Avoid
Do not reflexively order non-contrast "stone protocol" CT for all flank pain. The ACR guidelines emphasize that in patients with flank pain and negative urinalysis without history of urolithiasis, contrast-enhanced CT is more appropriate as it better characterizes alternative diagnoses 1, 2. The traditional teaching of "flank pain = stone protocol CT" leads to suboptimal diagnostic yield when pyuria is absent.