What is the most likely cause of gross hematuria, severe flank pain, and sandy urine caught on a urine strainer?

Urolithiasis (Kidney Stones)

The most likely cause of gross hematuria, severe flank pain, and sandy urine caught on a urine strainer is obstructive urolithiasis (kidney stones). This classic triad represents symptomatic stone disease with active stone passage, and the "sandy" material captured in the strainer is almost certainly stone fragments or gravel 1.

Why This Diagnosis is Most Likely

• Sandy urine with material caught on a strainer is pathognomonic for urolithiasis, as this represents visible stone fragments or crystalline material passing through the urinary tract 1
• Symptomatic gross hematuria with associated flank pain or renal colic is the classic presentation of urinary stone disease, occurring in over 80% of cases 1, 2
• The combination of severe flank pain and hematuria has urolithiasis as the primary etiology in the vast majority of emergency presentations, with noncontrast CT demonstrating sensitivity of 96-97% for detecting stones 1

Diagnostic Approach

Immediate Assessment

• Verify the presence of true hematuria by examining the urine visually and confirming with dipstick testing, which has 92.9% sensitivity for detecting hematuria in renal colic patients 3
• Assess pain severity and location, noting that renal colic typically presents as severe, colicky flank pain that may radiate to the groin as the stone moves distally 1, 2
• Examine the captured material from the urine strainer, as visible stone fragments confirm the diagnosis and can be sent for stone analysis to guide prevention strategies 1

Risk Stratification for Complications

• Evaluate for signs of infection including fever, chills, or systemic symptoms, as infected obstructed systems (pyonephrosis) require urgent decompression 1
• Check vital signs to exclude shock, as patients with hemodynamic instability require immediate hospital admission 2
• Assess for complete obstruction indicators including anuria, bilateral symptoms, or solitary kidney, which mandate urgent urologic intervention 1

Imaging Strategy

First-Line Imaging

• Noncontrast CT abdomen and pelvis is the reference standard for evaluating suspected urolithiasis, with sensitivity as high as 97% and specificity of 98% for stone detection 1
• CT provides critical information including stone size, location, degree of hydronephrosis, and presence of complications such as perinephric fluid or stranding 1
• Moderate to severe hydronephrosis on imaging predicts higher risk of stone passage failure and may guide decisions about conservative versus interventional management 1

Alternative Imaging When CT is Contraindicated

• Renal ultrasound combined with plain radiography (KUB) can be used as an alternative approach, with combined sensitivity of 79-90% for detecting clinically significant stones 1
• Ultrasound is 100% sensitive and 90% specific for detecting ureteral obstruction (hydronephrosis, ureterectasis, perinephric fluid), though it may miss stones in the first 2 hours before secondary signs develop 1

Management Priorities

Immediate Pain Control

• Analgesia must be administered to provide pain relief within 30 minutes of assessment, as this is a Grade A recommendation for patients with severe flank pain 2
• Patients failing to respond to analgesia within one hour require immediate hospital admission, representing treatment failure that necessitates escalation of care 2

Stone Passage vs. Intervention

• Stone size is the primary predictor of spontaneous passage, with stones <5 mm having >90% passage rate, while stones >7 mm rarely pass spontaneously 1
• The presence of moderate to severe hydronephrosis increases risk of stone passage failure and should prompt early urologic consultation 1
• Captured stone fragments should be sent for analysis to determine composition (calcium oxalate, uric acid, struvite, cystine) and guide metabolic evaluation and prevention strategies 1

Critical Pitfalls to Avoid

Do Not Assume Benign Etiology Without Imaging

• While urolithiasis is most likely, other serious conditions can mimic this presentation including renal cell carcinoma with hemorrhage, Page kidney (subcapsular hematoma), or even leaking abdominal aortic aneurysm in patients over 60 years 2, 4
• Painless gross hematuria has a stronger association with malignancy (30-40% risk), so if pain resolves but hematuria persists, complete urologic evaluation with cystoscopy and CT urography is mandatory 1, 5

Do Not Delay Evaluation for Infection

• The absence of fever does not exclude infected obstructed system, and urine culture should be obtained before antibiotics if infection is suspected 1
• Infected hydronephrosis (pyonephrosis) requires urgent decompression via percutaneous nephrostomy or ureteral stent placement, as medical management alone is insufficient 1

Do Not Ignore Red Flags for Urgent Intervention

• Solitary kidney with obstruction, bilateral obstruction, or obstruction with acute kidney injury all require urgent urologic intervention regardless of stone size 1
• Patients over 60 years with severe flank pain require particular vigilance for vascular emergencies like aortic aneurysm, which can present similarly 2

Follow-Up After Stone Passage

• All patients with confirmed urolithiasis should undergo metabolic evaluation including 24-hour urine collection for stone risk factors (calcium, oxalate, citrate, uric acid, cystine) 1
• Stone analysis guides prevention strategies, with calcium oxalate stones requiring different interventions than uric acid or struvite stones 1
• Repeat imaging at 3-6 months may be indicated to assess for residual stone burden or new stone formation, particularly in patients with recurrent disease 1